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.
