The poor tribological performance of Ti6Al4V titanium alloy severely limits its application in moving components. Although hydrogenated diamond-like carbon (a-C:H) coatings can effectively improve their wear resistance, the mechanism underlying the load-driven evolution of the friction interface remains unclear. This study systematically investigates the tribological behavior and interfacial dynamic evolution of a-C:H coatings under different loads via multiscale characterization. Results show that the a-C:H coatings significantly reduced the coefficient of friction (COF) and wear rate by 61.08% and four orders of magnitude, respectively. With increasing load, the COF decreased monotonically, while the wear rate first decreased and then increased, reaching an optimum at 10 N. Raman spectroscopy and transmission electron microscopy (TEM) analyses revealed that the load drove the evolution from a state dominated by iron oxides to a mixed phase and finally to the formation of continuous carbon transfer films. Critically, higher loads accelerate the formation rates of the carbon transfer film while promoting its graphitization, enabling rapid surface coverage that suppresses oxidative wear. This kinetic control facilitates the transition in the friction mechanism from oxidative wear to efficient shear lubrication by the carbon transfer film. This work establishes that the kinetic regulation of the interfacial pathway is the central mechanism through which load optimizes tribological performance, providing a foundational principle for the load-adaptive design of surface coatings on titanium alloys.

With the development of the shipbuilding industry, it is necessary to improve tribological properties of polyether ether ketone (PEEK) as a water-lubricated bearing material. In this study, the sulfonated PEEK (SPEEK) with three distinct chemical structures was synthesized through direct sulfonated polymerization, and high fault tolerance and a controllable sulfonation degree ensured the batch stability. The tribological and mechanical properties of SPEEK with varying side groups (methyl and tert-butyl) and rigid segments (biphenyl) were compared after sintering in a vacuum furnace. Compared to the as-made PEEK, as the highly electronegative sulfonic acid group enhanced the hydration lubrication, the friction coefficient and wear rate of SPEEK were significantly reduced by 30% and 50% at least without affecting the mechanical properties. And lower steric hindrance and entanglement between molecular chains were proposed to be partially responsible for the lowest friction behavior of SPEEK with methyl side groups, making it a promising and competitive option for water-lubricated bearings.

A hybrid of halloysite nanotubes decorated with titanium dioxide nanoparticles (HNTs@TiO2 ) was synthesized by the sol-gel method and then mixed with ultra-high molecular polyethylene (UHMWPE) by melt compounding to enhance its wear resistance properties. The incorporation of HNTs@TiO2 increased the crystallinity as well as the hardness of UHMWPE nanocomposites, which benefited less prone to plastic deformation during the friction process. In addition, the UHMWPE/HNTs@TiO2 maintained a high ductility character with a slight decrease in tensile strength compared to pure UHMWPE. With the addition of 3 wt% HNTs@TiO2 , the UHMWPE nanocomposite achieved a remarkably low friction coefficient of 0.073 and a reduced wear rate of 6.67 x 10(-6) mm(3)/N center dot m. These values represented a 32.4% decrease in friction coefficient and a 43.9% decrease in wear rate compared to pure UHMWPE. The improvement in wear resistance was due to the dislodged TiO2 and HNTs had good synergistic rolling effects at the counterface. Furthermore, the wear scan morphology observation revealed that the transferred HNTs@TiO2 -based materials could help to improve the quality of the tribofilms, which alleviated the abrasive wear from the metallic counterpart. This work offers a feasible way to enhance the wear resistance of UHMWPE nanocomposite without sacrificing the high ductility for expanding its engineering applications.

The existing materials for liquefied natural gas (LNG) cryogenic submersible pump bearings are very susceptible to wear and failure in LNG environments where oil lubricants and greases are ineffective, posing a major hazard to the safety of LNG storage and transportation. Therefore, searching for a type of material with excellent cryogenic tribological properties for improving the life of LNG bearings has become a huge challenge for re-searchers. Invar 36 alloy, as a low expansion nickel-titanium alloy, is used in control instruments, moulds, laser control equipment, and materials of LNG transport hull at temperatures below-162 degrees C. However, there is a lack of research data in the field of bearings. Currently, the Si3N4 ceramic balls are widely used in ceramic hybrid ball bearings and exhibit excellent tribological properties. In this work, the tribological performance of Invar 36 alloy is mainly investigated against Si3N4 ceramic ball under extremely cryogenic and dry conditions using the modified ball-on-disk tribometer with a cryogenic module, with temperatures as low as-196 degrees C. All experiments are performed at loads of 0.5 N, 1 N, 1.5 N, and 2 N, and at temperatures of 20 degrees C, 0 degrees C,-78 degrees C, and-196 degrees C, respectively. The experimental results show that the coefficient of friction (COF) and wear rate decrease with temperature and load, with a minimum value of-196 degrees C. The Invar 36 alloy exhibits excellent tribological properties, whose COF decreases gradually from 20 degrees C to-78 degrees C. However, as the temperature drops to-196 degrees C, the COF decreases abruptly, reaching a minimum value at-196 degrees C. On the contrary, the COF gradually increases with load. In addition, a commercial bearing grade material (G95Cr18 steel) is tested and compared under the same conditions, proving that Invar 36 alloy exhibits better tribological properties than G95Cr18 steel, with a wear rate 55.43% lower than G95Cr18 steel at-196 degrees C. Further simulation comparisons demonstrate that, due to its extremely low coefficient of thermal expansion, Invar 36 alloy exhibits higher toughness and strength than G95Cr18 steel under cryogenic conditions. This study complements the tribological data of Invar 36 alloy and G95Cr18 steel against Si3N4 ceramic balls under different temperatures and loads and provides important theoretical guidance and technical support for the bearings' future development of LNG cryogenic submersible pump.

Thermoplastic polyurethane (TPU) is widely used in daily life due to its characteristics of light weight, high impact strength, and compression resistance. However, TPU products are extremely flammable and will generate toxic fumes under fire attack, threatening human life and safety. In this article, a nanohybrid flame retardant was designed for the fire safety of TPU. Herein, Co3O4 was anchored on the surface of exfoliated ultra-thin boron nitride nanosheets (BNNO@Co3O4) via coprecipitation and subsequent calcination. Then, a polyphosphazene (PPZ) layer was coated onto BNNO@Co3O4 by high temperature polymerization to generate a nanohybrid flame retardant named BNNO@Co3O4@PPZ. The cone calorimeter results exhibited that the heat release and smoke production during TPU combustion were remarkably restrained after the incorporation of the nanohybrid flame retardant. Compared with pure TPU, the peak heat release rate (PHRR) decreased by 44.1%, the peak smoke production rate (PSPR) decreased by 51.2%, and the peak CO production rate (PCOPR) decreased by 72.5%. Based on the analysis of carbon residues after combustion, the significant improvement in fire resistance of TPU by BNNO@Co3O4@PPZ was attributed to the combination of quenching effect, catalytic carbonization effect, and barrier effect. In addition, the intrinsic mechanical properties of TPU were well maintained due to the existence of the PPZ organic layer.

Biodegradable polylactide (PLA) has been widely utilized in people’s daily lives. In order to improve the fire safety of PLA, ammonium polyphosphate (APP) was self-assembled onto the surface of serpentine Ni3Si2O5(OH)4 through the electrostatic method, followed by mixing with PLA by melt compounding. The APP-modified serpentine (serpentine@APP) dispersed uniformly in the PLA matrix. Compared with pure PLA, the PLA composite with 2 wt% serpentine@APP reduced the peak heat release rate (pHRR) and total heat release (THR) by 43.9% and 16.3%, respectively. The combination of APP and serpentine exhibited suitable synergistic flame-retardant effects on the fire safety enhancement of PLA. In addition, the dynamical rheological tests revealed that the presence of APP and serpentine could reduce the viscosity of PLA composites. The plasticizing effects of APP and serpentine benefited the processing of PLA. The mechanical properties of PLA/serpentine@APP maintained suitable performance as pure PLA. This study provided a feasible way to enhance the fire safety of PLA without sacrificing its mechanical properties.

With the rapid development of the world economy and the accelerating industrialization process, the industrial oily sewage faces multiple difficulties and severe challenges. It is difficult for the traditional oil–water separation methods to meet the processing requirements for a large amount of oily wastewater. Researchers have inspired by the superhydrophobic phenomenon on the surface of animals and plants in nature, and a variety of specific wetted oil–water separation materials to treat and purify of the oily sewage have been achieved. In this paper, an oleophilic hydrophobic silica sol is prepared by a sol–gel method, and a lipophilic hydrophobic coating is dip-coated onto a stainless steel mesh. The effects of sol ratio, impregnation times, and the heat treatment temperature on the hydrophobicity of the modified mesh coating were investigated. The hydrophobic properties, surface morphology, and the coating elements of the modified hydrophobic mesh were characterized by Optical Contact Angle meter, Focused Ion Beam Scanning Electron Microscope, Atomic Force Microscope, X-ray Photoelectron Spectroscopy, and Fourier Transform Infrared Spectroscopy. The durability of the mesh was examined by ultrasonic cleaning and acid–base immersion. Separation experiments were carried out on a variety of different oil–water mixtures. The results suggest that the modified mesh has better lipophilic hydrophobic properties. Consistent lipophilic hydrophobic properties were achieved under ultrasonic cleaning conditions and in solutions within different pH = 3–11. The modified mesh has good separation and reusability for different types of oil–water mixtures.

采用不同粒径的碳化硼作为硼源,以氧化铈作为催渗剂,在非惰性气氛保护下对TC4钛合金表面进行固体渗硼.利用场发射扫描电镜(FESEM)、背散射电子成像(EBSD)、X射线衍射(XRD)、UMT摩擦磨损试验机对渗硼层的微观组织结构和摩擦学性能进行研究.结果表明,TC4钛合金表面渗硼层为双相硼化物;随着碳化硼粒径的增加,TiB层厚度与渗层总厚度减少,渗层硬度约为60(HR30N),硼化物层摩擦系数约为0.2,碳化硼的杂质组成对渗层有较大影响.

Ti6Al4V (TC4) slices were boronized with rare earth oxide (RE) addition in the agent at 950°C (below β phase transus of TC4). The morphology, phases, properties and structures of TC4 matrix and boride layers were studied. The results show that the boride layer on the surface of TC4 consists of TiB2 and TiB dual compounds. The boride layer is compact, uniform and less porous compared with that obtained at 1050°C (above β phase transus of TC4), and the hardness profile and brittleness of the layers are improved to a certain extent. Lower temperature boronizing can effectively prevent the growth of coarse β phase grains. Duplex microstructure is obtained in TC4 matrix, and the work piece distortion is reduced.

Rare earth and B atoms were penetrated into Ti6Al4V(TC4) alloy surface using the solid powder technique without protective atmosphere.The rare earth-borided,borided and TC4 alloys were corroded in the 3.5wt% NaCl and 5wt% H2SO4 solutions,respectively.The X-ray diffraction analysis shows that the borided layer on the TC4 surface is composed of TiB2 and TiB.Scanning electron microscopy study shows that the outer TiB2 layer has a flat growth front,while the inner TiB layer appears serration.Some pinholes present in the outer layer,which may be due to the Kirkendall effects caused by the co-diffuse of Ce and B atoms synchronically.The Tafel polarization curve shows that,in the 3.5wt% NaCl and 5wt% H2SO4 solution,the corrosion resistance of the samples follows the order of borided,rare earth-borided and TC4 alloy.

Boronizing on the surface of titanium alloys can greatly improve their wear resistance performance.The research status of boronizing on the surface of titanium alloys at home and abroad was summarized in the present paper.The formation mechanism and growth kinetics of titanium compounds in solid boronizing method were discussed.The factors,such as substrate structure,composition of boronizing agent,boronizing temperature,oxygen partial pressure etc,can influence the final structure of the boride layer.A thicker boride layer can be gotten at a temperature close to the β transus temperature.The growth kinetics of TiB and TiB2 layers in the double structure obeys the Fick second diffusion law d2 = K·t.

Solid powder boriding experiment was carried out on TC4 titanium alloy surface with method of RE(rare earth)-boriding at the temperature of over 1000°C. By means of XRD, SEM and EDS, phase composition, microstructure and morphology of TC4 titanium alloy after RE-boriding were investigated. The effect of rare earth on phase composition was discussed. Results of the experiment showed that the diffusion layer was composed of top-layer TiB2 and sub-layer TiB whiskers with the highest thickness being 25μm. The XRD results revealed TiB-TiB2 biphasic B-Ti compounds layer formed on the surface of TC4 after RE-boriding. The high content of B and Ce in the surface layer showed rare earth increased the absorption and concentration of B atoms.

In this paper, Ni0.6Si0.2Al0.6Mn1.6O4 compounds with negative temperature coefficient (NTC) property were fabricated using NiO, SiO2, MnO2 and Al2O3 as raw materials. The effect of ball milling time on phase composition, microstructure and electrical stability of the compounds was studied. The results showed that the particle size of calcined powder decreased with the increase of ball-milling time, resulting in a decreased B25/85 constant, activation energy and resistance drift ΔR/R0 (%) of the Ni0.6Si0.2Al0.6Mn1.6O4 compounds. Meanwhile, it was found that activation energy increased with the decrease of the density of the compounds, and the resistance drift ΔR/R0 (%) was less than 0.02% when the ball-milling time reached to 48h.

The pack RE-boronizing experiments were carried out on TC4 titanium alloy surface at 1000, 1050 and 1100°C for 5, 10, 15, 20 h, respectively. By means of XRD, SEM and EDS, the phase composition, microstructure and morphology of TC4 titanium alloy after RE-boronizing were investigated. The effect of rare earth on phase composition, microhardness and wear resistance was discussed. The results showed that the diffusion layer was composed of top-layer TiB2 and sub-layer TiB toothed with the largest thickness of about 25 μm. Adding RE in the agent could increase the TiB2 content in the treated layer, and promote the absorption and concentration of B atoms on the substrate surface and significantly improve microhardness and wear resistance. The results showed that the microhardness of diffusion layer was gradient distribution from 3300HV0.01 to 1800HV0.01.

A pack boriding technique was employed to ohtain a hard coating on the surface of Ti-6Al-4V alloy in this paper.The diffusion process was carried out at various temperatures ranging from 1000 ℃ to 1100 ℃ for 5 to 20 hours.The microstructure,morphology and the phase composition of Ti-6Al-4V alloy after boriding were investigated.The diffusion behavior of Ti,Al,V,B elements in boronizing process was also discussed.The results showed that the thickness of diffusion layer ranged from 0.8 μm to 15 μm for different boriding parameters.The biphasic boron-titanium compounds TiB-TiB2 layer have formed on the surface of Ti-6Al-4V alloy.The XRD results of surface layer revealed that the amount of TiB and TiB2 increased with temperature rising.Furthermore,the surface B atoms reacted with Ti of Ti-6Al-4V matrix that led to the reduction of Ti in transition region.The microhardness value of TiB2 to TiB was gradient distribution ranged from 2200 HV0.01 to 1100 HV0.01.And the hardness value in the transition region was higher than the Ti-6Al-4V matrix.

The pack boronizing experiment was carried out on TC4 titanium alloy surface with a method of solid powder boronizing. By means of XRD, SEM and EDS, phase composition, microstructure and morphology of the TC4 titanium alloy after boronizing were investigated. Diffusion behavior of elements in boronizing process was discussed. Results show that after holding at 1000, 1050 and 1100 degrees C for 5 h and 20 h, the thickness of diffusion layer ranges from 0.8 mu m to 15 mu m. The outer surface is TiB2 and the inner surface is TiB whiskers. XRD patterns reveal TiB-TiB2 biphasic B-Ti compounds layer is formed after boronizing of TC4 alloy and the peak position of TiB2 and TiB increases with the temperature rising. Furthermore, EDS shows, after having been absorbed by TC4, surface B atoms react with Ti of the matrix resulting in the reduction of Ti in transition region. At the same time, Al and V elements begin to diffuse into the matrix and enrich in the near-interface region. Microhardness of the diffusion layer is of gradient distribution; the hardness value of TiB2 to TiB whiskers ranges from HV0.01 22 000 MPa to HV0.01 11 000 MPa and the hardness value in the transition region is higher than that in the matrix.

TiO2 porous films were prepared directly on the surface of TC4 titanium alloy by constant voltage anodic oxidation using sulfuric acid,TC4 and stainless steel plate as electrolyte,anode and cathode,respectively.The micro-morphology of the TiO2 porous films on the substrate was observed by SEM.Meanwhile,phase composition of the porous films on the titanium alloy substrate was determined by XRD.The effects of oxidation process parameters such as the voltage,the anodization time and the concentration of sulphuric acid on the phase composition of TiO2 porous films were investigated.The results showed that,oxide films of titanium alloy after anodic oxidation were heterogeneous TiO2 porous films with pore size ranging from 90nm to 240nm.The XRD analysis showed that the oxide films prepared with different oxidation process parameters were all consisted of annatase and rutile phases.In 0.5mol/L sulfuric acid electrolyte,the annatase and rutile TiO2 appeared when the voltage was higher than 100V or anodization time was longer than 5min,and with the voltage and time increasing the content of rutile TiO2 increased gradually.The annatase and rutile TiO2 appeared with 0.3mol/L sulfuric acid electrolyte at constant voltage(≥120V),and the content of rutile TiO2 increased at first and then decreased with the increasing concentration of sulfuric acid.

TiO2-PTFE compound coating was prepared on the surface of TC4 titanium alloy by the special chemical and physical method.The lubricant film was composed of hard anodic oxidation film and PTFE with low friction factor,which had excellent self-lubricant property.Microstructure and morphology,phase composition and element composition of TiO2-PTFE compound coating were investigated.The effect of anodic oxidation treatment process and coating time on the coating volume of PTFE was discussed.Results of the experiment showed that after anodic oxidation,the nanometer TiO2 porous film was consisted of annatase and rutile phases formed on TC4 titanium alloy.After being coated with PTFE,the surface and film hole were covered by PTFE polymer.The PTFE coating volume kept stable after the samples of TC4 titanium alloy being treated in different voltages and different oxidation time.As the coating time prolonging,the PTFE coating volume increased rapidly in the first 5-20min,the coating volume increased slowly after more than 20min.

Dual titanium boride layers consisting of continuous TiB2 top-layer and TiB whisker sub- layer were formed on the surface of Ti6Al4V alloy using powder-pack bonding technique. An iso-thickness diagram of the whole boride layer was fitted with the data of thickness of the coating, treatment time and process temperature using Sigma Plot10.0 software. Growth kinetics of the titanium boride layer were analyzed by measuring the extent of penetration of TiB2 and TiB whisker as a function of bonding time in the range of 5-20 h and bonding temperature in the range of 1000-1100 degrees C. By the linear regression analysis of growth kinetics of titanium boride layer, the diffusivity K and average diffusion activation energy (Q) of boron atoms in Ti6Al4V alloy were calculated, respectively.