Advancements in aviation and aerospace technology have led to increased utilization of high-temperature alloys in more extreme environments. Thermal barrier coatings (TBCs) are commonly used for the surface protection of high-temperature alloys, which are often subjected to thermal corrosion erosion during service. This places higher requirements on the performance of TBCs, and the conventional atmospheric plasma spraying process can no longer meet these requirements. Laser surface modification technology can be employed to enhance the stability and corrosion resistance of TBCs at elevated temperatures, thereby satisfying the demands of extreme service conditions. Furthermore, investigating the impact of pre-oxidation time on the thermal corrosion performance of laser alloying-modified yttria-stabilized zirconia (YSZ) TBCs is of paramount importance. Atmospheric plasma spraying was employed to prepare NiCrAlY and YSZ coatings on the surface of Inconel 718, a nickel-based superalloy, following sandblasting to create a double-layered TBCs. The prepared TBCs were placed on a bench. A layer of 0.1 mm of 10% TiC and 90% CYSZ powder was then spread on the surface of the coating. Finally, the self-healing material TiC was fused to the coating using a 1 kW fiber-coupled laser fabrication system. The parameters were laser power of 130 W, scanning speed of 5 mm / s, and scanning spacing of 2 mm. The samples were then placed in a high-temperature chamber furnace at 600 degrees C after ultrasonic cleaning. Subsequently, the samples were placed in a high-temperature chamber furnace at 600 degrees C for 4 and 8 h to undergo a pre-oxidation treatment. They were then subjected to a hot corrosion test in a corrosive salt mixture comprising 25% NaCl and 75% Na2SO4 at 900 degrees C for 4 h. A comparative study of the effect of pre-oxidation time on the microstructure, phase composition, and thermal corrosion behavior of the coating was conducted. The surface of the laser-alloyed TBCs were more smoother and denser than that of the plasma-sprayed TBCs. Following the pre-oxidation treatment, the self-healing agent TiC was oxidized to TiO(2 )by exposure to O atoms in air. This resulted in volume expansion caused by the increase in TiO2 content, which allowed the cracks to be repaired. This made it difficult for corrosive salts to penetrate the coating and reduced the products of hot corrosion, such as Y-2(SO4)3 and m-ZrO2. Pre-oxidation treatment can improve the hot corrosion resistance of the laser surface-modified TBCs; an increase in the pre-oxidation time improves the hot corrosion resistance: the laser surface-modified TBCs with a pre-oxidation treatment of 8 h showed the best hot corrosion resistance. Pre-oxidation heat treatment can promote the TiC self-healing material oxidation reaction in advance to fill part of the cracks to achieve crack self-healing, inhibit corrosive salt penetration into the coating, and reduce the occurrence of hot corrosion reaction. This study proposes the use of a laser to melt TiC as a self-healing material in TBCs. This approach differs from previous methods of testing high-temperature oxidation performance, that have employed high-temperature oxidation to evaluate coating durability. The pre-oxidation process represents a significant strengthening mechanism for laser surface-modified YSZ TBCs and is therefore a highly beneficial technique for the future development of excellent hot corrosion-resistant TBCs. The proposed innovation entails the utilization of pre-high-temperature oxidation to replace the coating with self-healing materials, thereby facilitating the absorption of oxygen, expansion of volume to fill cracks, reduction of corrosion infiltration, and consequently, enhancement of the hot corrosion resistance of high-temperature alloys.
A mining pick is a cutting tool used in coal mining,roadway boring,and tunnel construction and consists of a carbide tip,body,and handle.With increasingly harsh mining conditions,the hardness and proportion of rock in the tunnel increase.High stress and strong impact loads cause severe wear problems in picks,making them the most consumed components in mining operations.Therefore,the rock-cutting wear degradation mechanism of a pick should be studied to conduct a suitable strengthening process.To clarify the wear degradation behavior and wear distribution law of the pick,the interactive wear evolution between the pick and granite was investigated using a custom-made pick wear tester.Changes in the tooth surface temperature,vibration acceleration,and wear characteristics at different cutting distances were systematically studied,and the wear degradation mechanism in different tooth surface regions was revealed using a thermal imager,vibration acceleration sensor,electronic balance,three-dimensional scanner,and scanning electron microscope.The results showed that wear and temperature increase occurred on the tooth surface of the pick.As the cutting distance increased,the wear loss of the pick increased almost linearly,accompanied by a gradual expansion of the wear area on the tooth surface from the tip to the entire tooth surface.Because of the friction-induced heat effect,the wear region of the tooth surface correlated well with the temperature field distribution,and the tooth surface temperature gradually increased with an increase in the wear area.A strong impact load was generated,and the vibration acceleration peak-to-peak value increased remarkably during rock cutting by the high-hardness pick tip,whereas the low-hardness pick body experienced sliding friction with the uncut/cut rock block,and the vibration acceleration peak-to-peak value was much smaller than that of the impact process.In addition,the amplitude-frequency characteristics of the impact and friction phases were different.During the impact phase,the vibration acceleration was primarily a high-amplitude oscillation signal with a relatively simple signal composition,whereas during the friction phase,the vibration acceleration consisted of low-amplitude,random,and complex frequency components.The uneven forces on both sides of the pick under asymmetric loading and a unilateral rotational moment caused the pick to rotate.Owing to the"self-sharpening"effect,the wear degree of pick tip and body was almost uniformly distributed along the circumference.The main wear mechanism of the pick tip was impact wear.Under the combined action of the impact load and high temperature,a dense rock particle accumulation layer formed on the pick tip.Owing to the high hardness and protection of the rock particle accumulation layer,the wear volume of the pick tip was much smaller than that of the pick body,despite the higher impact load.The wear volume of the pick body was 19.5 times greater than that of the pick tip.The entire pick body can be divided into severe wear and slight wear regions from top to bottom.The main wear mechanism in the severe wear region was abrasive wear,which accounted for 97％of the total pick body volume loss.The slight wear region was dominated by plastic flow,with almost no material removal.Constantly intruding rock particles mix into the pick body material,eventually leading to the formation of a mechanically mixed layer.This study clarified the wear distribution law and degradation behavior of the pick tooth surface,which will provide technical support for the high-performance strengthening and repair of picks.
Micromotion wear is prevalent in the aerospace, marine, chemical, and nuclear energy industries. TC4 is sensitive to fretting wear due to its poor tribological properties and limited work-hardening capability. The blade is a key component of aero-engines, and the service conditions are harsh, including centrifugal force, high temperature, gas excitation, and vibration. The most prominent issue is that rotor vibration causes periodic separation and contact between the blade root and the rim surface, leading to small-amplitude relative motion and alternating stress at the contact surface. This results in severe fretting wear at the blade root, which is a typical case of tangential micromotion wear. To improve the anti-fretting wear characteristics of the TC4 alloy surface and expand its application scenarios, the surface of the TC4 alloy was treated with laser shock peening (LSP) using an Nd:YAG solid-state laser. A study of the treated surface morphology revealed that LSP had minimal effect on the phase structure of the base metal. The laser shock peening technique enhances the comprehensive mechanical properties of the base metal without introducing thermal effects. It is practical, controllable, and induces a nanocrystalline layer on the alloy surface. There have been few studies on the fretting wear behavior and mechanism of LSP-treated TC4 alloy under different displacement amplitudes. In this paper, fretting wear damage models are established under various displacement amplitudes (50 mu m, 100 mu m, 150 mu m, 200 mu m) using an SRV-IV fretting wear tester. The fretting wear performance of the TC4 alloy before and after LSP treatment at different displacement amplitudes is analyzed, as well as the effect of nanocrystalline grains on fretting wear behavior before and after LSP. A QUANTA FEG 450 field emission scanning electron microscope (SEM) with an integrated EDS spectrometer was used to characterize the microstructure, elemental composition, and distribution within the wear regions. An OLYMPUS OLS5000 laser scanning confocal microscope (LSCM) was employed to characterize the 3D morphology of wear scars, wear interface profiles, and wear volume. A D8 DISCOVER X-ray diffractometer (XRD) was used to analyze the phase composition in the wear region, enabling the study of tangential micromotion wear behavior of the nanocrystalline layer on the surface of LSP-treated TC4 alloy at room temperature. Additionally, a two-mode fretting wear model was developed to investigate the fretting behavior and material damage mechanism of LSP-treated TC4 alloy. The results showed that LSP refined the internal microstructure of the alloy, introduced a high density of dislocations, reduced surface wear, decreased the friction coefficient, and improved the friction and wear performance of the strengthened surface. It significantly reduced fatigue spalling and the formation of microcracks in the contact area, effectively inhibiting crack initiation and propagation. Compared to untreated TC4 alloy, the LSP-treated alloy exhibited less variation in wear interface damage across different displacement amplitudes. Surface grain refinement due to LSP led to oxidation of the refined grains under frictional heat, resulting in a surface oxygen content significantly higher than that of titanium, which increased progressively with displacement amplitude. LSP effectively enhances the anti-fretting wear performance of TC4 alloy across various displacement amplitudes. The refined grain layer promotes the formation of a stable third-body layer with the substrate under the influence of frictional heat, altering the wear pattern on parts of the surface and reducing overall damage.
Vacuum coating equipment, a key high-tech device, has become a dominant technology in the surface treatment industry owing to its cost-effectiveness and low environmental impact. It has been widely utilized in new-generation information technology, aerospace technology, and energy. Currently, conventional coating equipment faces limitations because the revolution, autorotation, and inclination of the workpiece cannot be independently controlled or continuously controlled in multiple directions. This has resulted in application bottlenecks for downstream emerging industries, precision, and complex workpieces. To achieve coupling control of multiple degrees of freedom, a bending-arm hybrid-driven variable-angle thin-film sputtering platform was designed. The device integrates the bending arm transmission control component with multiple independent operating revolutions, rotation, and inclination swing drive mechanisms. The synergistic movement of each mechanism realizes coupling control between the different degrees of freedom. During the coating process, the workpiece realized independent linkage and continuous variable-angle automatic control of three degrees of freedom (revolution, autorotation, and inclination swing) within 0-90 degrees. The three movements were independently driven and controlled by three 42 series two-phase stepper motors and 256 subdivision stepper motor drivers to adjust the speed ratio and tilt angle, which can realize rotation and rotation motion control at angles of 0-90 degrees. The overall structure contains a shell, worktop, transmission tower, bending-arm hybrid control mechanism, revolution motion mechanism, self-rotation motion mechanism, and tilt angle swing transmission mechanism. The shell supported and sealed all the internal mechanisms of the device, and the drive assembly provided power for revolution and autorotation. The self-rotation motion mechanism drives the transmission shaft to realize the autorotation of the sample, and the orbital motion mechanism drives the central transmission tower to realize the revolution of the sample. The bending-arm hybrid transmission mechanism was connected to the inclined swing transmission mechanism through the drive shaft and medium-type mechanism. The innovatively designed medium-type hybrid transmission mechanism can stably and synchronously transmit the rotational operation of autorotation and the lifting and lowering motions of the inclination swing to achieve hybrid transmission. In addition, the bottom of the sample plate was designed with a heating plate and a thermal insulation blanket, which was embedded with a plurality of ceramic heating rods and temperature sensors, which can realize the heating and temperature control within 0-700 degrees C. Emergency power cutoff and stop protection functions were also designed. When the equipment is in the acceleration or constant-speed operation stage, the electromagnetic clutch is energized to directly transmit the power output of the motor to the drive gear. When the equipment was in a deceleration or emergency shutdown state, the electromagnetic clutch was de-energized, and the motor was disconnected from the drive gear. The overall structure achieves a high degree of automation, structural reliability, and easy maintenance. The device has high technical versatility, which can address issues related to traditional coating equipment, such as the small adjustment range of the tilt angle and the inability to automatically coordinate control. In addition, to meet the sputtering needs of emerging downstream industries, the as-designed hybrid drive platform can further reduce the space size, reduce the overall structural weight, and optimize the spatial layout of the three rotary motion systems, making the hybrid drive system more miniaturized and portable and reducing the production and operation costs. This technology holds substantial potential for multi-directional, continuous sputtering of intricate workpieces in advanced manufacturing.
TiB2 coatings are expected to have broad applications in wear-resistant fields owing to their high hardness, good wear resistance, and high thermal stability. However, these coatings are extremely brittle and prone to fracture during use. Existing research, both domestically and internationally, has introduced nitrogen into TiB2 coatings to form nc-TiN / a-BN nanocomposite structures to improve the coating toughness. However, it was found that even the introduction of a small amount of nitrogen leads to the formation of a significant amount of amorphous BN, resulting in a decrease in the coating hardness. To optimize the coating performance, this study uses high-power pulse magnetron sputtering, and the deposition temperature is varied to prepare the Ti-B-N coatings. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to analyze the microstructure and composition of the Ti-B-N coatings. A microhardness tester, scratch tester, and friction and wear testing machine are used to measure the hardness, film / substrate adhesion strength, and friction and wear properties of the Ti-B-N coatings. The effects of the deposition temperature on the structure, friction, and wear properties of the Ti-B-N coatings, as well as their wear mechanisms, are investigated. The results indicate that, as the deposition temperature increases, the kinetic energy of the sputtered particles is enhanced, as is their diffusion ability, which compacts the already deposited particles, resulting in a smoother and denser coating surface. Boron (B) in the target material is preferentially sputtered onto the substrate surface over titanium (Ti), causing the Ti-B-N coating to have a higher percentage of B than the target material. As the deposition temperature increases from 100 to 200 degrees C, the Ti content slightly decreases, and the B content slightly increases. When the deposition temperature reaches > 200 degrees C, there is no significant change in the Ti and B content. When the deposition temperature varies from 100 to 300 degrees C, h-TiB2 and Ti3B4 phases are detected in the coating; when the coating deposition temperature reaches 400 degrees C, only the h-TiB2 phase is detected. As the deposition temperature increases, the surface of the Ti-B-N coating gradually becomes smoother and denser, the hardness of the coating increases from 2 855 to 3 994 HV0.01, and the residual stress decreases from 0.9 to 0.3 GPa. When the deposition temperature is 400 degrees C, the coating is the smoothest and densest, with the highest hardness and the least residual stress. When the deposition temperature is 300 degrees C, the coating has the lowest friction coefficient and wear rate, which are 0.5 and 1.1 & times;10(-3) mu m3N(-1)mu m(-1), respectively, indicating the best wear resistance. This study indicates that Ti-B-N coatings deposited at 400 degrees C exhibit higher hardness, stronger adhesion, and lower tensile stress compared to those deposited at 300 degrees C. However, the friction rate significantly increases, suggesting that in this case, the primary factors influencing the frictional performance of the coating are not the hardness, adhesion strength, or internal stress. The average friction coefficient of the Ti-B-N coating deposited at 300 degrees C is 0.5, which is significantly lower than the coefficient of 0.8 at 400 degrees C. This demonstrates that under certain conditions, the friction coefficient is the main determinant of the frictional performance of the Ti-B-N coatings. By optimizing process parameters, such as the deposition temperature, it is possible to control the friction coefficient of the coating, thereby enhancing its overall frictional performance.
TiAl alloys are used as moving parts in spacecraft, such as jet engine turbine blades, and typically experience friction and wear in complex working environments, which has a significant effect on working stability and service life. In recent years, with the progress of science and technology, the machining accuracy, surface quality and sub-surface properties of TiAl alloy parts have been an increased demanded for their use in aeroengines. Therefore, it is essential to determine the micromechanical behaviors of gamma-TiAl in the friction process, and the surface deformation and damage mechanisms. However, traditional experimental methods have limitations in determining the microscopic mechanical behavior and deformation mechanism, whereas the molecular dynamics simulation method can perform dynamic observations of the microscopic deformation and defect evolution of materials at the atomic level. Therefore, in this study, the nano-scratching behaviors of gamma-TiAl single crystals and polycrystals are investigated using molecular dynamics simulation. The differences in friction, wear performance, and plastic deformation between single crystals and polycrystals are compared, and the effects of the scratch speed and scratch depth on the friction and wear performance are elucidated. The results show that a single crystal presents greater frictional resistance with a larger friction coefficient during the nano-scratch process, and better wear resistance is also proven because of fewer removed atoms and lower stacking heights when compared with polycrystals. As a single crystal has a regular crystal structure along the scratch direction, the wear atoms at the front and both sides of the indenter are uniformly stacked. However, the randomness of the grain orientation and the existence of grain boundaries in the polycrystals lead to asymmetric atomic packing at the front and both sides of the scratch region. The movement of the indenter causes obvious deformation in the contact area; the crystal atomic structure of the contact area becomes amorphous, and many atoms removed by wear move forward with the indenter. Polycrystals and single crystals show significantly different deformation behaviors and stress-strain characteristics induced by friction action. Friction leads to high shear strains in the scratch regions of the single crystal and strip strain zones on the {111} <111> slip system, suggesting that a large plastic deformation occurs within a single crystal. Friction promotes strain and stress concentrations at the grain boundaries in the polycrystalline model, thereby reducing plastic deformation within the polycrystalline grains. Analysis of the defect evolution indicates that the impact of the indenter on the surface of a single crystal causes the nucleation and expansion of many Shockley partial dislocations, and the grain boundaries become the source of dislocation nucleation in the polycrystals, leading to the formation of stacking faults within the grains around the indenter. Simultaneously, compared with the single crystal model, the limitation of the grain size in the polycrystal causes the dislocation and stacking faults to expand in a smaller space; thus, the dislocation density is significantly smaller, and the dislocation distribution is more complex. An increase in both the scratch speed and scratch depth results in an increase in friction and wear. A higher scratch speed can facilitate the activation of dislocations, and the accumulation of dislocations induces strain hardening of the substrate, leading to an increase in friction and normal forces. The number of atoms removed also increases with the scratch speed, indicating that the surface is more worn at high speeds. A greater depth represents a larger contact area, indicating that a greater external force is required to move the indenter, thus increasing friction and normal forces. Similarly, a larger scratch depth indicates that more volume is removed by wear, and more atoms are removed. These results are important for the development and design of high-performance TiAl alloys.
Aluminum oxide films have outstanding optical, mechanical, and corrosion resistance properties. Thus, aluminum oxide films have extensive applications in the field of electronic devices and display panels. HiPIMS achieves high ionization rate of sputtered particles through high peak power, enabling the deposited films to exhibit higher density and mechanical properties. be difficult to recover from a poisoning state under HiPIMS discharge. Therefore, when applied to the deposition of alumina films,HiPIMS exhibits strong sensitivity to reactive gases. The sensitivity of HiPIMS to reactive gases will lead to lower efficiency and increased difficulty of aluminum oxide films. In the deposition of alumina film layers, the oxygen flow rate is usually controlled at a critical value of target poisoning to obtain aluminum oxide films with high degree of oxidation. For HiPIMS technology, the critical oxygen flow rate is not conducive to stable discharge, while low oxygen flow rate will significantly deviate the composition of aluminum oxide films from the stoichiometric ratio. Deviation from the stoichiometric ratio will significantly decrease the optical transmittance and insulation properties of aluminum oxide films. To address this, the experiment utilized an anode layer ion source to generate ionized oxygen and directly transport it to the substrate. These oxygen particles react with aluminum particles to form films. The anode layer ion source allows the Al particles deposited on the substrate to be fully oxidized at a lower oxygen flow rate. Therefore, the anode layer ion source can significantly reduce the oxygen content in the target discharge area. Low oxygen flow rate also improves the stability of HiPIMS discharge. The experimental results show that, since HiPIMS operates under the condition far from target poisoning, the coverage rate of the insulating film on the target surface is low. Low insulation film coverage enables HiPIMS to achieve high-stability discharge and efficient deposition. Through SEM observation of the cross-sectional morphology, it is found that even at a target-to-substrate distance of 40 cm, the deposition rate of the alumina film can still reach 3 mu m/h. At a lower oxygen flow rate, the ion source acts as an auxiliary oxygen ionization agent. Ionized oxygen generated from ion source has stronger chemical reactivity, enabling the alumina film to be more fully oxidized. Therefore, EDS results show that the prepared aluminum oxide films have high oxygen content. At oxygen flow rate of 40 mL/min, far below the critical value for target poisoning, the Al/O ratio in aluminum oxide film can reach 0.69. The Al/O ratio means aluminum oxide film with near stoichiometric ratio is obtained. Since the film deposition is performed within the range of oxygen flow rates below the critical point of target poisoning, HiPIMS discharge exhibits good stability. The optical properties of the aluminum oxide films are not affected by arcing. The average optical transmittance of the aluminum oxide film can reach 95.2%. The high-energy characteristics of stable discharge by HiPIMS enable sputtered particles to have stronger migration ability, resulting in aluminum oxide films with high density and flatness. The dense structure endows the aluminum oxide films good mechanical properties, and the aluminum oxide film obtained at oxygen flow rate of 40 mL/min had a hardness of up to 945 HV. The dense structure also enables the alumina film to exhibit corrosion potential of -0.44 V and corrosion current of 10(-6). (88) A in electrochemical testing. With the assistance of a high-power ion source, the free electrons in the aluminum oxide film almost disappear, significantly improving the surface resistance and insulation properties. The surface resistance of the alumina film layer prepared at a flow rate of 40 mL/min reaches 10(9.51) Omega/sq, and the insulation strength reaches 62 V/mu m.
In pressurized water reactors (PWRs), the fuel cladding is in service for a long time under extreme environments, such as high temperature, high pressure, high flow rate, and strong radiation. Flow-induced vibration (FIV) is caused by the high-speed flow of coolant through fuel rods, which subsequently leads to grid-to-rod fretting (GTRF). GTRF is the primary cause of fuel cladding failure in PWRs worldwide and may lead to a series of major accidents, such as radioactive material leakage. Effectively reducing or preventing GTRF is an important issue that must be urgently addressed in the field of nuclear energy research. Cr-based coatings are among the most promising candidate materials for accident-tolerant fuel (ATF) cladding, and studying their fretting wear resistance is crucial for enhancing the safety and durability of nuclear reactors. Four types of Cr-based coatings-Cr, CrN, CrAlN, and CrAlSiN-were deposited on the surface of the zirconium (Zr) alloy using magnetron sputtering technology, and their microstructures and phase compositions were analyzed. Fretting wear tests in a B-Li water (3.5 mg / L Li+1 000 mg / L B) environment were conducted to explore the fretting wear behavior and wear mechanisms of the Zr alloy and different coatings. The ball-plane point contact configuration was utilized in the fretting wear test, with the friction pair consisting of an Si3N4 ceramic ball. The test parameters were set as follows: displacement amplitude of 100 mu m, load of 10 N, frequency of 10 Hz, and 10(5) cycles. The results show that different coatings have particles formed by metal droplets on their surfaces, which are typical features of coating surfaces prepared using magnetron sputtering technology. The different coatings have dense surface structure and higher hardness than the Zr alloy; the hardness of the CrAlN coating is the highest at approximately 550 HV0.2, while that of the Zr alloy is the lowest at approximately 200 HV0.2. The CrN coating has the smoothest surface, with a roughness of only 0.10 mu m, while the roughness of the Cr coating is the highest at 0.25 mu m. The Cr coating is mainly composed of the Cr phase, whereas the CrN, CrAlN, and CrAlSiN coatings are mainly composed of the CrN phase. The wear resistance of the Zr alloy is significantly improved by different coatings, and their wear depth and rate are evidently reduced compared with those of the Zr alloy. The generated oxide wear debris plays a crucial role. The hardness of the chromium oxide produced by the different coatings is higher than that of zirconia produced by the Zr alloy. In addition, the hardness of the coatings is significantly higher than that of the Zr alloy, making the different coatings more wear resistant. The wear degrees of the CrN and CrAlSiN coatings are similar and the lowest, with a wear rate of approximately 1 / 7 that of the Zr alloy and a wear depth of approximately 1 / 5 that of the Zr alloy. The wear mechanisms of Zr alloy are mainly adhesive, abrasive, and corrosion wear, whereas those of the different coatings are mainly abrasive and corrosion wear. The accumulation of wear debris from different coatings is mainly concentrated at the edge of the wear scar, with a large number of furrows and sparse distribution of wear debris in the center area of the wear scar, and no adhesive wear occurring. Based on its smoothest surface morphology, lowest roughness, higher coating thickness under the same preparation process, lowest average friction coefficient in fretting wear test, and best wear resistance, the CrN coating is a better choice than the CrAlSiN coating. By adjusting the proportions of various elements in Cr-based coatings, incorporating alloying elements, optimizing the preparation process, and employing other methods, the performance of Cr-based coatings, including their hardness and wear resistance, can be significantly enhanced. This topic has profound research significance. The aforementioned research findings play a pivotal role in improving the performance of ATF materials, elucidating wear mechanisms, and fostering technological advancements and practical applications.
The development of the electronics industry has resulted in the widespread use of electronic connectoraus as key components. However, the issue of surface corrosion, which severely affects their performance and reliability, is becoming increasingly prominent. As the main protective layer of electronic equipment, Zn-Ni alloys do not provide satisfactory wear resistance and hardness, which implies that they easily fail or generate corrosion cracks in corrosive environments. Currently, studies pertaining to the performance of Zn-Ni alloy surface passivation films are few. Therefore, the corrosion behavior of a hexavalent chromium (Cr(VI)) passivation film on the surface of Zn-Ni alloys is investigated in this study. The microstructure, elemental distribution, and corrosion resistance of passivation films on Zn-Ni-plated surfaces of electronic components are compared using high-resolution electron microscopy, surface-energy spectroscopy, and Raman spectroscopy. The aim is to compare the performances of electronic-component surface-plating and Cr(VI) passivation films under two different processes. The effects of different processes on the passivation films are elucidated to provide new ideas for investigating passivation-film properties. For Sample 1, scanning electron microscope results show relatively sparse surface cracks constituting 51% of the total area ratio, thus indicating a low surface tension, and that the cross-sectional morphology presents a clear layered structure. Results of energy-spectrum analysis show that the Zn-Ni distribution on the surface is not uniform and that Ni enrichment occurs in some areas, with the thicknesses of the Ni, Zn-Ni alloy, and Cr(VI) conversion layers being 16, 61, and 3 & micro;m, respectively. The Ni and Zn mass fractions are 14.4% and 72%, respectively, and the corrosion resistance is reasonable. Results of Raman spectroscopy indicate an acidic environment on the surface of the samples, as well as peaks at 886, 443, and 730 cm(-1) for Cr2O72-, ZnO, and CO32-, respectively, which are likely due to the presence of pollutants in the surface film-forming process or in the environment. Four typical points on the cross-section of Sample 1 are examined using Raman spectroscopy, and the results show clear Cr(VI) peaks, thus confirming the existence of a Cr(VI) passivation layer in Sample 1. For Sample 2, SEM results show that a densely cracked surface constituting 79% of the total surface area, and that the cross-sectional morphology shows a structure comprising three plating layers. The results of energy-spectrum analysis show a uniform Zn-Ni distribution on the surface without enrichment, with the thicknesses of the Ni, Zn-Ni, and Cr(VI) conversion layers being 12, 35.5, and 3 & micro;m, respectively, and Ni and Zn mass fractions of 13.5% and 71%, respectively, thus indicating the better corrosion resistance of Sample 2. Cr(VI) shows peaks at 851, 996, and 351 cm(-1) for CrO42-, SO42-, and of Ni(OH)(2), respectively, which is primarily due to the concentration and acidity of the solution. Raman test results indicate a concentration difference on the surface. Additionally, Raman results of the cross-section show a peak at 846 cm(-1) for Cr(VI), thus proving the presence of a Cr(VI) transformed layer in Sample 2.
WC series coatings have become indispensable high-performance hard-coating materials across a multitude of industrial sectors because of their exceptional hardness,wear resistance,and corrosion resistance.These attributes have made WC coatings essential components in various applications where durability and reliability are paramount.In the aerospace industry,WC-based coatings are extensively utilized in critical components,such as engine parts,bearings,and bushings.The high hardness and wear resistance of these coatings significantly mitigate component wear,thereby extending service life and enhancing component longevity and reliability.Additionally,their superior corrosion resistance ensures stable performance even under the most demanding and harsh operating conditions.Beyond these applications,WC coatings are also employed in aircraft landing gear and turbine blades,where they enhance both the impact and wear resistance,contributing to the overall durability and safety of these critical components.In the automotive manufacturing sector,WC series coatings are used in brake systems,transmission gears,and piston rings.Here,their low friction coefficient and high wear resistance play a crucial role in reducing mechanical component wear.This not only improves fuel efficiency but also significantly lowers maintenance costs.However,the high friction coefficient of the WC series of coatings results in severe wear of the counterpart.To address this challenge,this study introduces an innovative modification method aimed at endowing WC-based coatings with self-lubricating properties,while retaining their inherently high wear resistance.Using advanced laser processing technology,interconnected ortho-hexagonal grooves were meticulously created on the surface of the WC-10Co4Cr coating,forming a regular surface texturing network.This structural design serves multiple purposes:it enhances the mechanical interlocking between the coating and substrate,ensuring better adhesion and durability.In addition,it provides a reservoir for lubricant storage,which is a critical feature of the self-lubricating mechanism.Subsequently,the grooves are filled with fusible polytetrafluoroethylene(PFA),renowned for its excellent lubricating properties and thermal stability,via vacuum impregnation.This technique ensures uniform distribution of PFA within the grooves,providing a stable,continuous lubricant supply during operation.The combination of surface texturing and vacuum impregnation not only introduces an additional lubricant phase to the coating but also optimizes the lubricant storage and supply mechanism through structural design.The interconnected grooves act as a reservoirs for the PFA,ensuring its availability for lubrication,even as it is consumed during operation.This design significantly enhances the ability of the coating to maintain low friction under dynamic conditions,which is a crucial factor in reducing wear and improving efficiency.The friction factor of the WC-10Co4Cr-PFA composite coating was significantly reduced to 0.17,a marked improvement over the unmodified WC-10Co4Cr coating(0.36)and the coating with surface texturing alone(0.30).This substantial reduction in the friction factor indicates that the synergistic effect of laser texturing and PFA lubricant can significantly enhance the self-lubricating performance of the coating,enabling it to operate at low friction.This improvement is attributed to the effective integration of the mechanical benefits of the WC-10Co4Cr coating with the lubricating properties of the PFA.More importantly,the WC-10Co4Cr-PFA composite coating exhibited a unique self-replenishing mechanism.When the PFA lubricating film in contact with the coating is consumed because of wear,the viscosity of the PFA in the grooves decreases under the effect of frictional heat.Under the shearing action of the mating balls,PFA redistributed and repaired the worn surface lubrication film.This self-replenishing function ensures that the coating maintains a consistently low friction factor over an extended period of operation.In a rigorous 100-hour friction and wear test,the average friction factor of the WC-10Co4Cr-PFA composite coating remained at approximately 0.17,demonstrating its excellent self-lubrication life.In this work,the surface texture and vacuum impregnation of PFA resulted in a WC-10Co4Cr coating with excellent long-life,self-lubricating performance,providing a new idea and method for improving the lubricating performance of hard-wearing,wear-resistant coatings.
In marine environments,metallic materials are susceptible to various forms of corrosion,among which microbiologically influenced corrosion(MIC)is particularly significant.This type of corrosion is primarily induced by the activities of specific microorganisms such as sulfate-reducing bacteria(SRB).These mechanisms involve localized chemical changes caused by biological metabolic processes,such as acidification and acceleration of deoxygenation reactions.Such corrosion phenomena pose significant threats to the long-term reliability and durability of metals in marine environments,endangering critical engineering structures such as ships,offshore facilities,pipelines,and other infrastructures.Therefore,the effective inhibition of microbial corrosion and enhancement of the service life of metals in marine environments have become critical areas of research in materials science.To address this challenge,this paper troduces a novel TiC-based nanocomposite coating prepared using dual-cathode plasma sputtering deposition.The antibacterial and corrosion-resistant properties of the coatings were significantly enhanced by the incorporation of Ag nanoparticles(AgNPs).Dual-cathode plasma sputtering deposition is an efficient and controllable thin-film preparation technique capable of co-depositing multiple materials,thereby creating composite coatings with superior performance.In this study,AgNPs were uniformly distributed within the TiC nanocrystalline matrix,endowing the coating with remarkable antibacterial and microbiologically influenced corrosion resistance properties.Four representative strains were selected for experimental,evaluation:Gram-negative E.coli and S.typhi,Gram-positive S.aureus,and the fungus C.albicans.The antibacterial performance of the AgNP/TiC nanocomposite coating was assessed using the plate count method,which involves the quantification of the number of surviving bacteria after contact with the coating.The results demonstrated that the AgNP/TiC coating exhibited excellent antibacterial activity against all the tested strains,significantly reducing bacterial growth and reproduction.This effect is primarily attributed to the unique antibacterial mechanisms of AgNPs,including the release of silver ions and their interactions with the bacterial cell walls and DNA,which disrupt normal metabolic processes,ultimately leading to cell death.To further investigate the performance of the coating against SRB-induced microbial corrosion,we employed the paired reagent bottle method and most probable number dilution method.SRB strains were inoculated into artificial seawater,and changes in SRB populations in solutions exposed to the coating were analyzed.Compared with traditional TiC coatings and untreated titanium substrates,the AgNP/TiC coating significantly reduced the SRB population in the solution by three orders of magnitude.The incorporation of AgNPs effectively inhibited SRB adhesion and aggregation on the coating surface and prevented biofilm formation.Furthermore,the electrochemical corrosion behavior of the AgNP/TiC coating in SRB-inoculated artificial seawater was systematically studied using electrochemical techniques,including potentiodynamic polarization curves,electrochemical impedance spectroscopy(EIS),and Mott-Schottky analyses.Potentiodynamic polarization results indicated that the AgNP/TiC coating exhibited a higher corrosion potential and lower corrosion current density,demonstrating superior corrosion resistance.The EIS analysis further revealed that the passive film formed on the coating surface provided a high charge transfer resistance,significantly impeding the corrosion process.Mott-Schottky analysis showed that the semiconductor properties of the AgNP/TiC coating were markedly improved,which played a crucial role in enhancing its corrosion resistance.This study also revealed that the passive film formed on the coating surface exhibited unique microstructural characteristics.This passive film not only demonstrated high stability but also provided excellent isolation against corrosive media,thereby significantly enhancing the corrosion resistance of the material.The incorporation of AgNPs was pivotal in modulating the microstructure and surface chemistry of the coatings.The AgNPs enhanced the antibacterial activity of the coating by effectively suppressing microbial adhesion and proliferation.In contrast,the synergistic interaction between the AgNPs and TiC matrix improved the mechanical properties and durability of the coating.In this study,the comprehensive performance of a AgNP/TiC nanocomposite coating in a simulated marine environment was systematically investigated,highlighting its significant advantages in term of antibacterial and microbiologically influenced corrosion resistance.The findings demonstrate that the addition of AgNPs provides new insights into improving the coating performance and creates new avenues for developing coatings with efficient antibacterial and corrosion-resistant properties.This novel coating has significant application potential in shipbuilding,marine engineering,and other industries involving corrosive environments.
Currently, numerous challenges are faced in the detection of surface defects on hot-rolled strip steel. These include the difficulty of feature extraction caused by the complex background of crazing (Cr) defects, a weak response exhibited by small target defects such as pitted-surface (Ps), a lack of cross-scale fusion resulting from the different scales and morphologies of rolled-in-scale (Rs) defects, and the issues of a small number of samples and an uneven distribution of categories encountered. To meet the requirements for high accuracy of the surface defect detection algorithm for hot-rolled strip, a hot-rolled strip surface defect detection algorithm named RCS-YOLOv8, which is based on an improved YOLOv8, was proposed. Six surface defects, such as crazing and pitting-surface, were taken as the research objects to enhance the detection precision and robustness of surface defects in hot-rolled strip steel. To address the limitations of the original YOLOv8 in small object detection and multi-scale feature representation, improvements were made in three key areas. First, an enhanced receptive field and coordinate attention mechanism were introduced to construct the RCC (Receptive field & coordinate attention convolution) module. Feature extraction is enhanced by improved receptive field coverage and directional sensitivity; thereby, the recognition accuracy for densely packed objects is boosted. The constructed RCC module not only inherits the directional sensitivity of CA but also is enabled to extract detailed information with greater precision through enhanced receptive field adaptability provided by RFAConv (Receptive field attention convolution). Object localization capabilities are enhanced by the CA mechanism through the modeling of long-range dependencies in both horizontal and vertical directions. However, a fixed local receptive field is maintained by CA, which fails to fully optimize the flexibility of feature extraction. To address these limitations, an adaptive approach is employed by the RFAConv module to optimize feature extraction. Compared to traditional attention mechanisms, weights for different positions are learned by RFAConv to adaptively adjust the receptive field size, which effectively enhances local feature representation. Furthermore, the degree of attention paid to features across different receptive fields can be adaptively adjusted by RFAConv. Simultaneously, the CFC (Receptive field & coordinate attention cross-stage fusion) module, which integrates both RCC and C2f (Cross-stage partial fusion) architectures, enhances multi-scale feature representation capabilities while computational efficiency is maintained, enabling adaptive receptive field feature extraction. The core of the CFC module is considered to lie in the refinement of the multiple Bottleneck structural submodules that compose the C2f module. As the fundamental building block of the C2f module, structural refinement is undergone by the Bottleneck structure, where its standard convolutions are replaced with RCC modules. This modification, performed without altering the overall C2f framework, enables adaptive receptive field extraction capabilities; thereby, the feature modeling power of the C2f module is enhanced. For small targets, the P2 shallow multi-scale detection module SBA (Spatial Bi-directional attention) is proposed. The SBA module, a spatial bi-directional attention mechanism, is primarily applied to feature fusion in computer vision tasks. This module is designed to process multi-scale features, enabling effective integration between high-resolution and low-resolution features. Bidirectional pathways are established between high-and low-resolution features, while a P2 detection layer is incorporated to enhance shallow feature extraction capabilities. Through this approach, detection accuracy for objects at different scales is improved and spatial feature perception is strengthened. The RCS-YOLOv8 network was used to train and test the surface defect dataset of hot-rolled strip, and comparisons were made with the original model. Experimental results show that the average detection mean mAP and F1 score of the improved YOLOv8 algorithm on the NEU-DET dataset are 79.8% and 78%, respectively, which represent increases of 3% and 5% compared to the original model, and the floating-point operations of the improved algorithm are reduced by 2.4%. On the GC10-DET dataset, the mAP was increased by 4.2%. RCS-YOLOv8 not only achieves higher detection accuracy but also maintains a fast detection speed, which meets the requirements for both accuracy and real-time detection of industrial strip surface defects.
Magnesium alloy, recognized as the most promising functional structure integration material, has good ductility, machinability, electrical and thermal conductivity, and structural strength, and a low density. It has a wide range of potential applications in fields such as aerospace, national defense and military, transportation vehicles, 3C products, biomedicine. However, its poor corrosion resistance has become the main problem hindering its application. In this study, a two-dimensional layered double hydroxide (LDH) chemical conversion coating is prepared on the surface of a magnesium alloy, which has the characteristics of easy operation, low cost, environmental protection, and strong adhesion to the matrix, and can effectively prevent corrosion. Due to the unique anionic intercalation structure of LDH, studies have focused on the insertion of corrosion inhibitors into the interlayer to protect them from the displacement of corrosive media, such as Cl-. After the intercalation of the corrosion inhibitor, the morphology of the LDH can be changed, the barrier and shielding effects of the LDH coating can be improved, and the migration of aggressive ions can be hindered. The results show that, in addition to loading corrosion inhibitors in LDH, some corrosion inhibitors, such as benzothiazole, can be used as specific types of corrosion inhibitors, offer unique corrosion protection of AZ31B magnesium alloys. Furthermore, a dense bimetallic LDH coating on the surface of a AZ31B magnesium alloy without the addition of exogenous Mg2+ and Al3+ after hydrothermal treatment in an aqueous solution containing benzothiazole can provide effective corrosion protection. After the LDH coating is stripped off the surface of the magnesium alloy by mechanical bending, its crystal structure is characterized by X-ray diffraction (XRD), its functional group structure is characterized by Fourier transform-infrared spectroscopy (FT-IR), and its composition and structural morphology are characterized by scanning electron microscopy (SEM). Electrochemical tests are performed to confirm the excellent corrosion resistance of the prepared LDH coating. The results show that the sample supplemented with both C7H5NS and Na2CO3 is more uniform and denser than the sample supplemented with only C7H5NS. After adding benzothiazole and sodium carbonate to the aqueous solution, the corrosion current density is 1.23 & times;10(-7) A cm(-2), which is significantly lower than that of the blank sample. Furthermore, the corrosion inhibition efficiency is 90.5%, and the low-frequency impedance value is still higher than 10(5) Omega cm(2) after immersion in 3.5wt.% NaCl solution for 14 days. Benzothiazole has a significant inhibitory effect on the cathodic hydrogen evolution corrosion reaction, and the potentiodynamic polarization (PDP) results show that the cathode current density decreases more significantly. This indicates that the adsorption film formed in the cathode region is denser than that in the anode region. However, there are certain defects in the corrosion inhibitor adsorption film or precipitation film in the anode. As a result, the anode metal dissolution reaction further promotes the release of Mg2+, which reacts with the OH-produced by the cathode reaction and in the solution to form magnesium hydroxide precipitation. then reacts with Al3+ to form LDH, which is deposited on the surface of the AZ31 magnesium alloy. Compared with the blank sample, there is a difference in the surface coverage of the cathode and anode, which can further promote the dissolution of Mg2+ in the anode region. The release of a greater proportion of Mg2+ is more conducive to the formation of LDH, and the generated LDH layer is denser, which provides effective protection for the AZ31 magnesium alloy. After adding the Na2CO3 solution, the pH is approximately 10.5, which is conducive to the binding of Mg2+ and OH(-)and promotes the precipitation and formation of LDH. This corrosion inhibition mechanism not only improves the corrosion resistance and durability of the protective film but also provides a new perspective for corrosion inhibitors to improve the protection technology of magnesium alloys.
The numerical simulation method has been widely employed for efficient guidance of the preparation and further optimization of the service properties of protective ceramic coatings. These studies mostly focus on the research of structural stability mechanisms improvement of anti-corrosion capabilities, and anti-oxidation behavior promotion. The adsorption states of various corrosive molecules on the surface of protective ceramic coating surfaces are well known to be crucial factors that can determine anti-corrosion and anti-oxidation properties. Therefore, the different adsorption sites of oxygen molecules on the CrN(111) surface were studied systematically utilizing the first-principle of the density functional theory to investigate the underlying adsorption mechanism of oxygen molecules on the nitrogen-based protecting coating surfaces. By constructing stable oxygen molecular configurations at high symmetry adsorption sites on the CrN(111) surface, the adsorption energy, stable adsorption configuration structure, and electron states of the O-2 / Cr(111) adsorption system were calculated theoretically to expound the interaction mechanism of atoms in adsorption. The calculations revealed that O-2 molecules adsorbed at hollow-Cr sites on the CrN(111) surface exhibit the most intense interaction with the lowest adsorption energy of -5.17 eV. Optimizing the geometric structure of the O-2 / CrN(111) adsorption system significantly influenced oxygen molecular surface adsorption, whereby the surface atoms of the CrN(111) plane underwent an obvious structural relaxation phenomenon. The oxygen molecules at the different adsorption sites did not exhibit angular deflection. However, the distance between the top and sub-layer decreased from 1.20 angstrom to similar to 1.10 angstrom, and the bond length of the all-adsorbing oxygen molecules enlarged with a peak value of 1.36 angstrom at bri-Cr-Cr and hollow-Cr sites. Notably, the adsorbing oxygen molecules of bri-Cr-Cr site transferred to the hollow-Cr site, which also exhibited the lowest distance between the top layer and oxygen molecules, indicating that the hollow-Cr site is the most stable adsorption site of the O-2 / Cr(111) system. This aligns well with the adsorption energy results calculated above. As for the different adsorption sites of the O-2 / Cr(111) adsorption system, the charge transfer phenomenon between the adsorbed O atom and surface Cr and N atoms was detected to a large extent based on analysis of the electron density distribution and charge population, which indicated the ionic bonding interaction between the O atom and surface Cr / N atoms. The overlap and resonance of the orbit density peaks of the Cr 3s, 3d, and N 2p orbits with the O 2p orbit demonstrated obvious orbital hybridization occurrence. Accordingly, it can be reasonably deduced that the ionic and covalent bonds between the adsorbing oxygen molecule and CrN(111) surface atoms are the fundamental contributors to the formation of the stable adsorption system. Additionally, at the hollow-Cr adsorption site, the density of the energy states of the O-2 molecule ranged from -8.0 eV to -6.0 eV, exhibiting an obvious shrinking trend as the density of the states increased significantly. Meanwhile, the locality of 2p orbital of the O-2 molecule gradually enhanced, which also indicated that the ionic bond between the O-2 molecule and the surface Cr atoms was strengthened, further confirming that the hollow-Cr adsorption site acted as the most stable adsorption site of the O-2 / CrN(111) adsorption system. In summary, both ionic and covalent interactions typically co-exist between the adsorbed oxygen molecule and the surface Cr and N atoms, contributing directly to the formation of a stable O-2 / Cr(111) adsorption system with the hollow-Cr absorption site being the most favorable.
As the cornerstone of the digital economy, chips are advancing toward integration, low power consumption, intelligence, and functionality. Chemical-mechanical polishing (CMP) has become a critical technology for achieving ultrasmooth and defect-free global and local planarization in chip manufacturing. The abrasives in polishing slurry act as a "bridge" to facilitate the synergistic mechanical and chemical processes that are essential for high-precision material removal. Moreover, abrasives play crucial roles in achieving efficient, atomic-level, and smooth manufacturing of various materials, and they have become focal points of CMP research. Over the past few years, extensive efforts have been devoted to developing high-performance abrasives for chip manufacturing. In addition to being integral to the mechanical aspects of CMP, where they perform the physical removal of materials, abrasives also contribute chemically by interacting with the materials being polished. Hence, CMP performance is significantly influenced by the properties of the abrasives, including their dispersion stability, mechanical properties, morphology, particle size, and chemical reactivity. Maintaining the dispersion stability of abrasives is vital for prolonging the shelf lives of polishing slurries and minimizing defects, such as scratches. Furthermore, precise control over the morphology and size distribution of the abrasives can significantly reduce scratches on polished surfaces. Chemically reactive abrasives enable efficient material removal, which improves the overall polishing rate and surface quality. The research progress on typical abrasives used in CMP for semiconductor manufacturing is reviewed, with a focus on materials such as SiO2, Al2O3, CeO2, and diamond. SiO2 abrasives are especially renowned for their abilities to satisfy the ultra-high-precision surface quality requirements of advanced semiconductor devices as well as their versatility across a wide range of materials and processing conditions. SiO2 abrasives are essential for the manufacturing of modern electronics, particularly for applications that require exceptionally smooth and defect-free surfaces. Al2O3 abrasives are widely used in the CMP of substrates such as SiC, GaN, and sapphire, and they contribute to a favorable balance between performance and cost. CeO2 abrasives are highly effective for achieving efficient material removal and fine surface finishes owing to their unique combination of mechanical hardness and chemical reactivity, which makes them ideal for specialized CMP applications. Diamond abrasives are essential for planarizing ultra-hard materials, including diamonds and other hard substrates, for which conventional abrasives are ineffective. In addition to these conventional abrasives, there is growing interest in novel abrasives and the integration of energy-field-assisted polishing techniques. These techniques utilize external energy fields (such as electric, magnetic, or optical fields) to enhance the physical and chemical interactions between abrasives and substrates, thus helping overcome the limitations of conventional abrasives when working with hard or chemically inert materials by providing an additional energy input. Moreover, there is ongoing research on the behavior of abrasives at the nanoscale, as semiconductor manufacturing is advancing toward smaller and more complex devices. Advanced characterization techniques and computational simulations were also used to gain a deeper understanding of the CMP process at the nanoscale, with the aim of understanding the atomic-level interactions between abrasives and substrates. Improving the precision and efficiency of the CMP processes is crucial, particularly for the production of next-generation semiconductor devices. Additionally, a forward-looking outlook on the application of abrasives in chip CMP is provided, and the needs for continued process optimization and the development of novel abrasives are emphasized. Furthermore, the theoretical mechanisms that govern CMP behavior must continue to be explored, as this will provide a strong foundation for future innovation in the field. This study aims to provide valuable insights and theoretical support to guide future research and development in CMP for the purpose of ultimately driving advancements in semiconductor manufacturing technology.
Titanium alloys are widely utilized in aerospace, marine ships, biomedicine, and other fields owing to their lightweight, high specific strength, low elastic modulus, good corrosion resistance, and good biocompatibility. Although titanium alloys exhibit some degree of corrosion resistance owing to the oxide film on their surface, the naturally formed oxide film is thin and susceptible to degradation, resulting in limited corrosion resistance. In particular, in the harsh conditions of high-salt and high-humidity marine environments, titanium and its alloy parts will suffer severe electrochemical corrosion and crevice corrosion when working, which greatly limits their large-scale application. Micro-arc oxidation technology is widely used in metal surface protection because of its simple operation, green environmental protection, and induced strong adhesion between the film and the substrate. However, a single micro-arc oxidation film has holes and cracks on the surface, which limits its anti-corrosion performance. At present, the primary methods used to improve the performance are in-situ sealing by adding insoluble micro-nano particles and post-sealing methods combined with other surface technologies. Micro-arc oxidation technology combined with self-assembly of low surface energy materials has been used to construct superhydrophobic films on the surface of magnesium and aluminum alloys to improve their corrosion resistance. However, there are few related studies on titanium alloy surfaces. In this study, post-sealing was used to construct micro-nano structures on the surface of TC4 titanium alloy using micro-arc oxidation technology. Combined with the surface modification with low-surface-energy octadecyltrimethoxysilane, which not only provided it with a lower surface energy but also exerted a filling effect on the micropores and cracks produced by micro-arc oxidation, a long-term anti-corrosion superhydrophobic composite film was constructed on the surface of TC4 titanium alloy. The surface morphology, composition, and phase composition were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. The wettability and corrosion resistance of the film were tested using a contact angle measuring instrument and an electrochemical workstation, respectively. The results showed that the ceramic-based superhydrophobic composite film had TiO2 as the main component and was successfully constructed on the surface of the TC4 titanium alloy. Compared with the TC4 titanium alloy substrate, the water contact angle of the superhydrophobic film increased from 48 degrees +/- 2 degrees to 154 degrees +/- 1.8 degrees, and the corrosion current density decreased from 2.346x10(-6) Acm(-2) to 9.481x10(-10) Acm(-2), reflecting a reduction of approximately four orders of magnitude. The self-corrosion voltage increased from-0.480 V to 0.454 V, increasing by 0.934 V. The impedance increased by approximately two orders of magnitude, reaching up to 4.97x10(7) ). To assess the corrosion durability of the superhydrophobic film, the samples were immersed in 3.5wt.% NaCl solution for one week and exposed to air for one week, respectively. Even after these treatments, the impedance remained in the 107 ) range, indicating that the film exhibited sustained corrosion resistance. This performance is attributed to the micro-nanostructures within the superhydrophobic film, which capture and retain air upon exposure, forming a stable air layer on the surface. This air layer effectively prevents corrosive media from directly contacting the substrate, thereby enhancing both the corrosion resistance and durability of the coated sample. This study provides both experimental and theoretical foundations for the surface corrosion protection of titanium alloys and offers valuable insights for expanding their application in marine environments.
The surface morphology of cylindrical thrust pad has been proven to have an important influence on the lubrication performance about the water-lubricated thrust bearing of nuclear reactor coolant pump,in order to identify the lubrication influence of different radial position and depth of circumferential trapezoidal groove on the surface of cylindrical thrust pad.Based on the surface mesh of thrust pad,the surface texture deviation is considered,the surface texture of the cylindrical surface on the sector thrust pad and its circumferential trapezoidal grooves are constructed,and the simplified Reynolds equation is solved by finite difference method.The results show that the thickness of water film decreases with the increase of the depth of the circumferential trapezoidal groove on the thrust pad surface,when the pressure of water film increases,the temperature of water film increases slightly,axial stiffness and axial damping increase significantly,the lubrication performance of the thrust pad decreases when the pressure peak on the surface of the thrust pad is separated into two pressure peaks on the inner side and the outer side.Finally,compared with the different grooves,circumferential trapezoidal grooves fixed depth,as the radial position of groove moves from inside to outside,the minimum water film thickness decreases first and then increases,and the maximum water film pressure rises,falls and rises again,shows that the M-shaped change rule,the maximum water film temperature increases first and then decreases,and the axial stiffness and axial damping increases first and then decreases,when the depth of circumferential trapezoidal groove is less than 0.1 mm,the pressure peaks are not obviously separated and still have good lubrication performance,the lubrication performance does not change greatly when the depth of circumferential trapezoidal groove is greater than 0.3 mm.The minimum water film thickness decreases first and then increases with the change of the position of the circumferential trapezoidal groove of the thrust pad from the inside to the outside,and decreases by 0.41 times with the increase of the depth of the groove.The maximum water film temperature increases first and then decreases,and increases by only 1.5％with the increase of the groove depth,and increases by 0.5％with the increase of the groove depth.The power loss of water film lubrication increases first and then decreases,and increases by 1.45 times with the increase of groove depth.The average water film shear stress increases first and then decreases,and increases by 1.96 times with the increase of groove depth.The minimum water film shear stress decreases first and then increases,and the minimum negative pressure value of-0.045 MPa appears at the position where the depth of the circumferential groove is 0.1 mm and the radial width is 0.6 times of the pad width,and the absolute value of the minimum water film shear stress is less than ambient pressure of the medium 0.1 MPa is not prone to cavitation erosion.For the crown thrust pad,except axial stiffness and damping,the lubrication performance of the annular trapezoidal groove shows a downward trend,but a reasonable setting of the annular groove can significantly increase the axial liquid film stiffness while reducing the acceptable liquid film thickness,which has a good support for the stable operation of the nuclear reactor coolant pump rotor.At the same time,pay attention to control the negative pressure area of the water outlet side,so as to suppress the influence of cavitation erosion caused by negative cavitation pressure.When the groove is preferred,the cavitation pressure can be controlled at 10％of the standard atmospheric pressure,that is,a smaller negative pressure level-0.01-0 MPa.The above conclusions provide technical support for the surface topography design,high performance manufacturing and bench test of the water-lubricated thrust pad of the extended nuclear reactor coolant pump,and have a certain reference value for the reliability design and in-service operation of the nuclear reactor coolant pump on the surface trace limit of the thrust pad,and are helpful for the research on the influence of surface scratches and textures of other topographies on lubrication.
The spray-deposited 7055 aluminum alloy has ultra-high strength, excellent machinability, and good heat treatment performance. However, aluminum alloys often exhibit surface cracks and fatigue failures during service, which affect their service life and safety. Solution treatment is a common metal-material processing technology. By dissolving certain elements of the alloy into the matrix, the microstructure and properties of the alloy can be significantly improved. In this study, 7055 aluminum alloy was subjected to single-stage solution treatment at 470 degrees C for 2 h and double-stage solution treatment at 440 degrees C for 4 h + 490 degrees C for 30 min. Water quenching was carried out at room temperature, with a transfer time of less than 25 s. Through solution treatment of the spray-deposited 7055 aluminum alloy, it was observed that the microstructure of the alloy changed significantly. Hardness and tensile tests of the extruded alloy and the solution-treated alloys were carried out, and the average values of the sample data were taken. Finally, the fatigue life values of the three samples were obtained through tensile-tensile fatigue tests on the extruded, single-stage solution, and double-stage solution samples. To further study the effect of solution treatment on the microstructure and properties of the 7055 aluminum alloy, advanced detection techniques such as scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used. SEM can provide high-resolution surface and cross-sectional images to help observe the microstructure and defects in the material. EBSD can provide detailed information on crystal orientation and grain boundary distribution, which is helpful for understanding the microstructural characteristics of materials. The second phase, grain size, grain orientation, recrystallization evolution, fatigue properties, and fatigue fracture of the spray-deposited 7055 aluminum alloy during solution treatment were studied using SEM. Combined with the changes in alloy hardness, the optimal solution treatment process was determined, providing a research basis for optimizing the solution process of spray-deposited 7055 aluminum alloy. The microstructure of the alloy was controlled through the solution treatment process to improve its mechanical properties and fatigue resistance. The effects of the solution treatment process on the microstructure, fatigue properties, and fatigue fracture of the spray-deposited 7055 aluminum alloy were studied using SEM and EBSD. The results show that, after the two-stage solution treatment at 440 degrees C / 4 h + 490 degrees C / 30 min, the size of the insoluble phase Al2CuMg and the impurity phase Al7Cu2Fe in the matrix decreased, and the proportion of the second phase decreased by 10.2%. The degree of recrystallization improved, the grain boundaries became clearer, the grain size was more evenly distributed, and the hardness of the alloy significantly improved. The hardness values of the as-extruded alloy and the single-stage and double-stage solution-treated alloys were 101 HV, 134 HV, and 182 HV, respectively. Their tensile strengths were 356 MPa, 435 MPa, and 559 MPa, respectively. Tensile-tensile fatigue tests were carried out on the three samples: extruded state, single-stage solution, and double-stage solution. The test parameters were as follows: under a maximum stress of 300 MPa and a stress ratio of R = 0.1, three samples were selected for each state, and the average fatigue life values were obtained. The average fatigue lives at the 300 MPa stress level were 12 000, 34 000, and 56 000 cycles, respectively. The results showed that the two-stage solution treatment played an active role in improving the mechanical and fatigue properties of the 7055 aluminum alloy. This provides a reference for optimizing the heat treatment process of 7000-series aluminum alloys.
Lubricants are used in modern industrial applications to enhance energy efficiency and reduce material damage by minimizing friction and preventing wear in both sliding and rolling contacts. Zinc dialkyldithiophosphate (ZDDP), the most extensively used anti-wear additive in engine oils, has been the subject of extensive research over the past few decades. Studies have shown that ZDDP undergoes tribochemical reactions to form a robust phosphate glass-based tribofilm on friction surfaces, effectively preventing direct contact between two surfaces. Although significant progress has been achieved toward understanding the drivers of tribofilm growth, tribofilm formation has been considered to follow a stress-promoted thermal activation model. However, an ongoing debate, as well as extended discussion, persists regarding the precise nature of the underlying mechanism involved in the overall tribofilm formation process. To systematically investigate the key factors influencing tribofilm growth, we developed a non-Newtonian point-contact thermal elastohydrodynamic lubrication (EHL) model incorporating the Ghanbarzadeh tribofilm growth model under the assumption of smooth contact surfaces. The pressure is computed using the multigrid method, elastic deformation is determined using the multigrid integration method, and temperature field is analyzed using the sequential column sweeping technique. This model provides a detailed and comprehensive examination of how various influencing factors, such as temperature, pressure, shear stress, and slide-roll ratio, collectively affect and determine the distribution characteristics of the tribofilm thickness. Furthermore, the influencing mechanisms and underlying interactions of these factors are thoroughly explored and interpreted from the perspective of temperature variation. The results demonstrate that temperature is a critical driving factor for tribofilm growth. Even under EHL conditions, as the temperature increases, the increase in the solid surface temperature becomes more pronounced, resulting in a significant increase in the tribofilm thickness, which exhibits an exponential growth trend. Additionally, by comparing three lubricants with different friction properties, we observed that shear stress significantly promotes tribofilm growth. Specifically, lubricants with high EHL friction, characterized by their higher pressure-viscosity coefficients, generate greater shear forces, resulting in thicker tribofilms than those with low EHL friction. This finding validated the stress-promoted thermal activation model. Moreover, both the pressure and the slide-roll ratio significantly influence the thickness of the tribofilm. An increase in either parameter promotes tribofilm formation. Specifically, when the slide-roll ratio is relatively low, the influence of pressure on the thickness of the tribofilm is minimal and can almost be considered negligible. In contrast, as the slide-roll ratio increases to higher levels, the effect of pressure on the tribofilm thickness becomes increasingly significant and much more pronounced. In particular, when the slide-roll ratio is high, a significant increase in pressure causes a marked and considerable increase in the thickness of the tribofilm. This phenomenon can primarily be attributed to the combined and notable effects of the pressure and slide-roll ratio on the temperature of the contact surfaces. These changes in the temperature directly and significantly contribute to the variations observed in the tribofilm thickness. Consequently, the role of pressure in enhancing and promoting the tribofilm growth should not be underestimated and should be carefully considered. Under EHL conditions, the tribofilm formation process is primarily controlled and influenced by key factors such as shear stress, pressure, and temperature within the contact region, which is consistent with the well-established stress-promoted thermal activation model. Furthermore, in the context of EHL, a more accurate and comprehensive representation of the various factors that affect the growth of the tribofilm can be achieved by considering the variations in temperature within the contact region and thereby generating the distribution of the tribofilm.
Thermal barrier coatings (TBCs) technology has been widely employed in the thermal protection of aero-engine blades. The blade surfaces are coated with ceramic materials that exhibit excellent thermophysical properties, high-temperature stability, mechanical strength, and resistance to high-temperature corrosion, thereby ensuring the longevity of aero-engines. However, the traditional 6wt.%-8wt.% Y2O3-stabilized ZrO2 (YSZ), commonly used to prepare TBCs, undergoes a phase transition with severe volume expansion, rapid sintering and severe high-temperature melt corrosion above 1 200 degrees C, leading to premature coating failure. To address the increasing service temperature of high-performance aero-engine, developing the novel TBCs material is urgently required. Recent advancements in research of 'high-entropy' alloys have inspired the application of the composition design of novel ceramic materials. The synthesis and performance evaluation of high-entropy ceramic materials have thus provided new avenues for the development of novel TBC materials. The outstanding performance of the high-entropy ceramic materials is primarily attributed to four inherent effects: (1) thermodynamically high-entropy effect; (2) dynamically sluggish diffusion effect; (3) severe lattice distortion; (4) cocktail effect. Relevant studies have demonstrated that these four distinctive effects associated with high-entropy materials provide a degree of flexibility in composition design and property regulation, which is not present in traditional TBCs or single-component TBCs materials. Furthermore, the comprehensive performance of high-entropy TBCs ceramics is comparatively better, as evidenced reduced thermal conductivity, a coefficient of thermal expansion (CTE) that is well-matched with the alloy substrate, and the exceptional high-temperature stability. This paper presents a summary of the current research status of high-entropy thermal barrier ceramics offering an analysis of component design and performance optimization based on the characteristics and the nature of bonding in the crystal structure. The analysis covers five key aspects: thermal conductivity, thermal expansion performance, high-temperature resistance to sintering and phase stability, mechanical properties and resistance to high-temperature CaO-MgO-Al2O3-SiO2 CMAS corrosion. Elements with large mass disorder and ionic radius disorder are used for the synthesis of high-entropy TBCs materials to form a larger degree of lattice distortion, which can expand the phonon collision chances, decreasing the phonon mean free path and reducing the thermal conductivity. Anions and cations with minor differences in electronegativity can form ionic bonds with weak bonding strengths to obtain materials with higher CTE. Similarly, the formation of ionic bonds with strong bonding strength is beneficial for improving the mechanical properties, such as hardness and fracture toughness. The ions with the large radius difference compete for the same lattice site together, forming a more severe lattice distortion, which hinders matter diffusion. It leads to the sluggish diffusion phenomenon that contributes to high temperature stability. The concept of high entropy, based on the nature of multi-component single-phase solid solutions, offers a novel approach to the composition design and property regulation of novel TBCs materials, which has attracted considerable research interest. By summarizing and analyzing the radius disorder, mass order, and bond strength, the high-entropy thermal barrier ceramics with optimized composition based on the nature of ion can exhibit enhanced thermal physical properties, CTE, mechanical properties, high-temperature resistance to sintering and phase stability, and resistance to CMAS corrosion, exhibiting the potential for further development. However, the preparation and performance of high-entropy thermal barrier ceramic materials is the research mainstream, which is not entirely applicable. Moreover, several problems need further research and to provide solutions during manufacturing, thereby promoting its development and maturity, such as element segregation and phase transition. In this study, the theoretical guidance on the composition, design, performance optimization, and regulation of high-entropy TBCs materials and an outlook on the prospective applications is offered.
