Adhesive Wear Research Articles

Effect of hydrogen embrittlement on mechanical characteristics of DLC-coating for hydrogen valves of FCEVs

Diamond-like carbon (DLC) coating is a surface coating technology with excellent hydrogen permeation resistance and wear resistance. However, it is difficult to completely prevent hydrogen permeation, and when hydrogen penetrates into the coating layer, the DLC coating is adversely affected. Therefore, we investigated the effect of hydrogen embrittlement on the adhesion strength and wear resistance of the DLC coating layer. As the results of the research, the surface roughness of the DLC coating was increased by a maximum of 3.8 times with hydrogen charging, and the delamination ratio of the DLC coating reached about 58%. In addition, the Lc3, which refers to the adhesion strength corresponding to the complete delamination of the DLC coating, was decreased by a maximum of 2.0 N due to hydrogen permeation. In addition, the wear resistance decreased due to hydrogen permeation, and the exposed width of the substrate due to wear increased by more than 4 times. It was also determined that hydrogen blistering or hydrogen-induced cracking occurred at the interface between the DLC coating and the chromium buffer layer due to hydrogen permeation, which decreased the durability of the DLC coating.

Research on Prediction Methods for Eccentric Wear of the Slipper Pair in Axial Piston Pumps and Lubrication Performance Analysis

Abstract The axial piston pump (APP) is the core power component of hydraulic systems. Its friction pair wear can cause the degradation of piston pump performance until the function is completely lost or the service life is terminated. The slipper pair, prone to wear failure, is selected as the research object in this paper. The prediction method for the eccentric wear of the slipper pair is established, and the gradual change rules of the performance with wear accumulation are explored. The micro-surface rough peak contact and the stress state of the slipper pair are analyzed, and the mixed lubrication model of the slipper pair is established based on the elastohydrodynamic lubrication (EHL) model of the slipper pair. Grid discretization of a sealing belt of the slipper pair is carried out based on two-body abrasive wear and Archard adhesive wear models to improve the prediction method for eccentric wear of the slipper pair. The effectiveness of the proposed method is verified by a surface morphology analysis of the worn slipper. The results showed that the wear depth and wear width of the outer edge of the slipper bottom surface are positively correlated with the oil discharge pressure and the inclination angle of the swashplate, and negatively correlated with the rotational speed and the dynamic oil viscosity. The outer edge of the slipper is wedged after eccentric wear, and the hydrodynamic effect of the lubricating oil film of the slipper pair is enhanced. Hence, proper wear can improve the lubrication performance of the slipper pair.

Si-enabled self-lubrication and wear resistance of CrCoNiSi medium-entropy alloy films

High- or medium-entropy alloys have gained attention in coatings attributed to high wear resistance, with the formation of an amorphous phase. However, tailoring the crystal structure has limitations in improving both friction and wear characteristics due to the uncertain influence of amorphization on friction coefficients. In this respect, Si, known to increase glass-forming ability, can reduce the friction coefficient as a self-lubricating tribo-film formed by tribochemical reactions. However, tailoring Si content also affects crystal structures, defects, and mechanical properties, which require systematical investigations. Therefore, in this study, CrCoNiSi alloy films are fabricated with controlling Si content (0–13 at%) and sputtering power (5.8–13.7 W/cm2). The increase in Si content and sputtering power both produce identical microstructural evolutions, shifting from a crystalline towards an amorphous phase. In an amorphous film of high sputtering power, the high SiO2 fraction leads to dominant adhesive wear with delamination, thus contributing to the increase in wear rate. However, the Si addition alters the Si ion fraction of post-wear, forming Si-induced tribo-film, retaining abrasive wear, and consequently reducing the friction coefficient and wear rate. This Si addition would offer control over crystal structure and self-lubricating properties, enabling tailored mechanical and tribological properties.

Effect of WC particle size on the microstructure and tribological properties of high-speed laser cladding Ni/WC composite coatings

Ni/WC composite coatings with WC particle sizes of 30–65, 65–100, and 100–145 μm were prepared on 304 steel using high-speed laser-cladding (HSLC). The phase composition, microstructure, and wear mechanism of the composite coatings were studied. The dendrite-growth mechanism around WC with different particle sizes and the effects of WC with different particle sizes on the microhardness and tribological properties of the composite coatings were analyzed. The results demonstrated that the composite coating consisted of intermetallic compound Ni3Fe and secondary carbides W2C and (Cr, Fe)7C3. The composite coating exhibited good macroscopic morphology and uniform microstructure. The WC particle size obviously influenced the columnar and cellular dendrites in the coating. The microhardness values of the three groups of composite coatings were 419.35, 314.64, and 331.65 HV. The average friction coefficients were 0.4876, 0.5693, and 0.5439. The wear volumes were 0.001, 0.0015, and 0.002 mm3. The wear mechanisms included adhesive, abrasive, and oxidation wear mechanisms. The results verified that the WC coating with a small particle size possessed the best microhardness and tribological properties.

Tribological Performance Study of Low-Friction PEEK Composites under Different Lubrication Conditions

This study introduces a low-friction composite based on PEEK to improve its friction and wear properties. The composite incorporates PTFE as a solid lubricant and utilizes PPTA as a reinforcing material within the PEEK matrix. These components were prepared utilizing a compression molding method, followed by a series of exploratory experiments to identify the optimal preparation conditions for PEEK. This research assesses how the PTFE/PPTA/PEEK composites perform in terms of friction and wear under dry and oil-lubricated conditions. By examining wear tracks using scanning electron microscopy and white light interference microscopy, this study aims to uncover the wear mechanisms of PEEK and its composites under different lubrication scenarios. Results show that the main wear mechanisms for the PTFE/PPTA/PEEK composites and bearing steel are ploughing and adhesive wear. The presence of PPTA helps reduce wear by leveraging its strong fibers and thermal stability, while the coefficient of friction decreases as PTFE creates a smooth, solid lubricating film on the surface. Notably, PEEK composites containing 25 wt% PTFE and 6 wt% PPTA demonstrate the lowest wear rates and reduced coefficient of friction in both dry and oil-lubricated conditions.

Hybrid deposition of AlTiN/WN multilayer films with low compressive stress at low temperature

AlTiN/WN multilayer films with low compressive stress were deposited by arc evaporation and DC magnetron sputtering at a low temperature. The phase structure, morphologies, mechanical properties, wear behavior, and cutting performance of the AlTiN/WN multilayer films were evaluated. The results show that all the as-prepared AlTiN/WN multilayer films have fcc structure and exhibit (111) preferred orientation. The lowest value of −1.7 ± 0.3 GPa for compressive stress was obtained under low-temperature deposition. The film hardness increases as the temperature increases. High-temperature deposition provides higher energy to grow a dense film, which improves the film hardness. Increasing the WN layer thickness reduces the adhesion strength of the film. Compared with room temperature, the friction coefficients of the films against stainless steel reduce at high temperatures. This was attributed to lubricative oxides WOx formed on the wear surface at high temperatures. Dry cutting experiments were conducted and the longest service life of the coated tool reaches ∼3730 m. The worn flank surface shows that both adhesion and abrasive wear dominate the failure of the coated tools.

Analysis of friction-induced vibration and wear characteristics during high-speed train friction braking process

This study explored the evolution of friction-induced vibration (FIV) and wear in high-speed train friction braking through experiments, theoretical analysis, and numerical simulation. Experimental tests revealed that vibration behavior transitions from high-frequency modes at high speeds to low-frequency stick-slip at lower speeds. Theoretical analysis indicated that brake disc speed, coefficient of friction (COF), and contact stiffness affect system stability. Specifically, the system experiences high-frequency vibrations at high speeds due to mode coupling, and the friction block surface primarily undergoes abrasive wear mechanisms. At lower speeds, the system demonstrates low-frequency stick-slip vibrations induced by the combined effects of mode coupling and negative friction velocity slope (NFVS) characteristics, and the friction block surface mainly experiences adhesive wear mechanisms.

Current-carrying tribological behavior of textured Au/MoS2 coatings in vacuum

Sliding electrical contact has been widely used in spacecraft such as slip ring for solar windsurfing, and its service life directly affects that of the spacecraft. Au as a sliding electrical contact material has been widely used in aerospace equipment, but poor lubricity limits its service life. To address this issue, this study introduces MoS2 into the texturing holes of the Au coating, which can improve the lubricity, and maintain the continuity of Au and thus its conductivity. Additionally, the effect of texture density on the vacuum current-carrying tribological properties of the textured Au/MoS2 coating was investigated. The results indicate that texture not only reduces the mechanical properties of the coating but also affects the amount of MoS2 that can be filled. A high texture density greatly reduced the carrying capacity, leading to serious abrasive wear. However, low texture density results in serious adhesive wear owing to insufficient lubricity. Under an appropriate texture density, excellent vacuum current-carrying tribological behaviour can be achieved depending on the formation of a transfer film of MoS2 and Au, which maintains conductivity through Au and provides lubricity through MoS2. This study is of great significance in prolonging the service life of sliding electrical contacts and provides a new idea for the design of sliding electrical contact materials.

Cold sintering preparation of B4C@SiO2/20BP ceramic matrix composite and its dry tribological properties

To achieve low-temperature sintering of B4C ceramic, 'sol-gel' method is employed to create a B4C@SiO2 core-shell structure composite. Black phosphorus (BP) is exfoliated through 3 methods to obtain few-layer black phosphorene (FLBP) with sizes ranging from 100 µm to 1 µm. B4C@SiO2/20BP composite is successfully prepared through cold sintering process at 3 GPa and 90 °C, using NaOH solution as the transient liquid phase. The dry friction properties of B4C@SiO2/20BP composites with different sizes of FLBP are investigated in a ball-on-disc contact form. The findings reveal that as the FLBP size decreases, the friction coefficient gradually increases, inversely correlating with the wear rate. The wear mechanism shifts from adhesive wear to fatigue wear, leading to a diminishing anti-friction effect of FLBP.

Multi-objective optimisation of wheel-rail adhesion for high-speed trains with aerodynamic lift wings

A high-speed train with aerodynamic lift wings (aero-wings) is designed to improve train speed and mitigate energy consumption. Nevertheless, the impact of aero-wings on wheel-rail adhesion and safety remains uncertain. In this examination, a multi-body dynamics (MBD) model of a high-speed train integrated with aero-wings was first created. The influences of train speed, wheel-rail contact conditions, and aerodynamic lift on the wheel-rail adhesion, wheel wear, and dynamics performance were briefly investigated, indicating that aerodynamic lift degrades wheel-rail adhesion and dynamics performance but reduced wheel wear. Then, the multi-parameters matching optimisation design for sufficient wheel-rail adhesion and minimal wheel wear was conducted. The results indicate that, under dry contact and traction conditions, the minimum wear and optimal wheel-rail adhesion can be achieved when the train speed is about 440.62 km/h, the aerodynamic lift is about 24.48% of the vehicle weight, and the wheel wear optimisation rate is 25.38%. While the train speed of 549.54 km/h and an aerodynamic lift of 12.39% corresponds to the optimal results with wear reduction of 11.62%, under wet and braking conditions. This study provides valuable insights for determining aerodynamic load limits and formulating traction/braking control strategies for high-speed trains with aero-wings.

Pulse current electroforming of Ni-PTFE nanocomposite mold insert with long-lifetime and anti-adhesive properties

Polymeric micro features tend to deform and break under the demolding force during injection molding process, which becomes a bottleneck problem limiting its precision manufacturing. To reduce the polymer-mold interfacial adhesion, nickel-polytetrafluoroethylene (Ni-PTFE) nanocomposite molds with low surface adhesion and high wear resistance were manufactured via pulse current electroforming. The electrodeposited Ni-PTFE nanocomposite showed a good hydrophobic property and low friction coefficient (between 0.1 and 0.3) than pure nickel (0.78). Compared with direct current, pulse current electrodeposition was beneficial to reduce the crystallite size and internal stress, thus improving the wear resistance and reducing the cracking defects. The hardness of pulse current electrodeposited Ni-PTFE reached 442.3 HV, which was 51.7 % higher than that of pure nickel. Compared to nickel mold, Ni-PTFE nanocomposite mold significantly improved the dimensional accuracy of molded microfluidic chips. This study systematically investigates the Ni-PTFE nanocomposite electroforming process under both direct and pulse currents, which provides a new approach for the manufacturing of high-performance precision injection mold insert.

Tribological properties and wear mechanisms of laser cladded Cu-Mo coatings at 25–500 °C

Abstract Surface modification is the major means to improving the wear resistance of copper alloys. In this study, Cu-Mo coatings were prepared on Cu-Cr-Zr alloy by laser cladding, and the high-temperature tribological properties against 7075 aluminum alloy were explored. The results show that the coatings are the two-phase structure of Mo encapsulated in Cu-mesh. The hardness and resistivity of the coatings is 61–73 Hb and (3.2–6.3)×10−8 Ωm, respectively. The wear resistance of the coatings is determined by hardness that relates to Mo content at lower temperatures, and it controlled by the tribo-oxides layer that composed of Cu and Mo oxides at higher temperatures. As the temperature increases, the main wear mechanism of the coatings changes from abrasive wear to adhesive wear.

High temperature friction and wear behavior of Mo–Si–B/ZrB2 composites

The Mo–Si–B alloys with good wear resistance are prominent for high-temperature applications. In this work, the effects of ZrB2 content and test temperature on the tribological properties of the Mo–Si–B/ZrB2 composites at 25–800 °C were investigated. It indicates that the composites show an enhanced wear resistance, which can be ascribed to the improved hardness and formation of Zr-rich borosilicate layer by introducing ZrB2 particles. The main wear mechanism is abrasive wear accompanies with adhesive wear at 25–400 °C, where ZrB2 addition can reduce the wear loss. And adhesive wear dominates at 600–800 °C, where the formed tribo-layer can provide a good self-lubricity and is beneficial for improving the wear resistance of the composites.

Study on the tribological properties of MoB/Cu laminated composite materials fabricated by hot-pressing process

This work presents a novel method for fabricating MoB/Cu laminated composite materials which are distinguished by their strong interlayer bonding and unique microstructure. MoB ceramic layer can obviously improve the friction and wear properties of Cu matrix composites. The tribological properties on cross-sections of MoB/Cu laminated composite are studied with GCr15 (a typical high-carbon chromium bearing steel) ball as counterpart under dry friction conditions. When the friction angle is less than 30°, the wear rate (∼0.4974 × 10-4mm3/(N·m)) is reduced substantially by about 85 % compared to pure copper. The coefficient of friction of the composite ranges from 0.182 to 0.223 at a friction angle from 0° to 90°. A dense lubricating oxide film is formed during the friction process, effectively slowing down the adhesive wear and increasing the friction and wear resistance. After XPS (X-ray photoelectron spectroscopy) analysis, the main components of the lubricating film generated during the friction process are MoO3, B2O3, Al2O3, CuO, and Fe2O3.

Braking Performance of Fe-Based and Cu-Based Powder Metallurgy Pads Paired with C/C-SiC Disk on Full-Scale Dynamometer

In this study, the friction performance of copper-based (Cu-PM) and iron-based (Fe-PM) powder metallurgy pads was systematically compared and analyzed by performing a braking test paired with a C/C-SiC disk on a full-scale flywheel brake dynamometer, including coefficient of friction (COF), wear rate (Wr), and worn surface under dry and wet tests. The test procedure simulated the braking conditions on high-speed trains with initial brake speeds (IBS) from 50 km/h to 200 km/h, as well as under various brake clamping forces (FB). During dry tests, both pads exhibited high levels of COF. The mean value of average COF (µm) for the Cu-PM pad was 0.371, which was slightly higher than that of 0.358 from the Fe-PM pad. The stability of µm over the IBS ranged from 68% to 82% for Cu-PM pads under different FB, while it was from 82% to 85% for Fe-PM pads. However, during the wet tests, the mean value of µm dropped to 0.207 for Cu-PM pads, and with the minimum µm of 0.062; whereas, they were 0.344 and 0.188 for Fe-PM pads, respectively, showing a significant difference in the friction performance between the two pads. Additionally, the Wr of the Cu-PM pad was 0.110 cm3/MJ during dry tests, which was 17.3% lower than that of 0.133 cm3/MJ observed for the Fe-PM pad. After the brake test with the Cu-PM pad, the friction film primarily covered the Si/SiC-rich region of the disk, effectively inhibiting the plowing of SiC hard asperities onto the pad surface. However, the friction film predominantly covered the fiber-rich region of the disk after the test with the Fe-PM pad, and the exposure of hard Si/SiC-rich asperities would continuously plow the pad during braking and resulted in furrows on the surface of the Fe-PM pad. In terms of wear mechanisms, adhesion wear was the primary mechanism on the contact surfaces of the Cu-PM pad and the C/C-SiC disk, while abrasion dominated the interaction between the Fe-PM pad and the C/C-SiC disk. This study provides valuable insights for the application of C/C-SiC brake disks on trains.

High-temperature dry sliding friction and wear behavior of in-situ (Al3Zr+ZrB2)/AA6016 aluminum matrix composites

Aluminum alloy, a lightweight material, has poor friction and wear properties at high temperatures. Therefore, aluminum matrix composites were prepared by in-situ autogenous method to enhance the high-temperature friction and wear capability of aluminum alloys. (ZrB2+Al3Zr)/AA6016 in-situ aluminum matrix composites were prepared by in-situ reaction with the addition of mixed salts of potassium fluoborate (KBF4) and potassium fluozirconate (K2ZrF6). The materials were characterized by XRD, SEM, and EBSD. The friction and wear properties were investigated mainly by high-temperature friction and wear experiments combined with SEM and XPS. The results show that the wear resistance of (ZrB2+Al3Zr)/AA6016 aluminum matrix composites far exceeds that of their alloys under severe conditions of high temperature. The wear of AMCs first decreases and then increases with increasing temperature. The lowest wear rate was observed at an ambient temperature of 100°C, where the wear rate of AMCs was reduced by a factor of 2.7 compared to that of aluminum alloys. In addition, the enhancement effect of hard and heat-resistant particles was also due to the oxide film generated during friction on the abrasive scar surface layer of AMCs under this condition and the self-lubricating substance (H3BO3). The composite wear mechanism of AMCs was dominated by abrasive, oxidative, and adhesive wear as the test temperature increased.

Investigating the formability of 6061-T6 aluminum alloy sheets at elevated temperatures using experimental and numerical methods

The high weight-to-strength ratio of AA6061 aluminum alloys presents increased potential applications in industries such as automotive and aircraft. However, its limited formability at room temperature (RT) restricts its usage. Therefore, in the conducted study, the formability of AA6061-T6 sheets with a thickness of 2 mm was investigated at different temperatures in the range of RT up to 300°C. Both experimental and numerical methods were employed to investigate the forming limit diagram (FLD) of an AA6061-T6 sheet. The tests were conducted using a non-isothermal Nakajima standard die under dry contact conditions. Two damage criteria, the Johnson–Cook and the ductile fracture criterion (DFC), were used in a thermomechanically coupled finite element analysis in Abaqus/Explicit to predict fracture in the AA6061 sheet. To examine the impact of temperature on the friction coefficient in the punch and sheet contact, an atomic force microscope was used to measure the roughness of the sheet, after the FLD tests, were conducted at different temperatures. Results indicate an increase in FLD levels from RT up to 100°C, followed by a decrease, for temperatures surpassing 100°C. Experimental findings underscored the significance of the adhesive wear at elevated temperatures, acting as a decisive factor that hampers the material flow and the sheet deformation, in the contact between the sheet and punch.

Friction, wear, and corrosion behavior of nitrocarburized HT250 gray cast iron

This study employed friction and wear experiments on nitrocarburized HT250 gray cast iron, utilizing GCr15 cemented carbide balls as the friction pair, to investigate the friction behavior and wear mechanism of the compound layer, diffusion layer, and matrix. The findings indicate that the diffusion layer exhibits the highest wear resistance, followed by the compound layer, while the matrix shows the lowest wear resistance. At lower loads, the wear form of the compound layer is characterized by minor flaking wear, the diffusion layer exhibits minor flaking and abrasive wear, and the matrix displays minor adhesive wear accompanied by abrasive wear. With increasing loads, the wear form of the compound layer transitions to flaking and abrasive wear, the diffusion layer shows fatigue flaking wear, and the matrix demonstrates severe adhesive wear, fatigue flaking wear, and abrasive wear. Electrochemical impedance spectroscopy and potentiodynamic polarization were employed to study the corrosion behavior of the compound layer, diffusion layer, and matrix in a 3.5 wt% NaCl solution. The results indicate a 27.7 % decrease in the corrosion current density of the compound layer compared to the matrix, with the diffusion layer exhibiting a corrosion current density two orders of magnitude lower than both the matrix and compound layer. In electrochemical impedance spectroscopy, the diffusion layer shows the highest impedance modulus, largest phase angle amplitude, and circular arc radius. It shows that the corrosion resistance of HT250 gray cast iron is improved after nitrocarburizing, especially the diffusion layer.

Microstructure, hardness, and tribological properties of CoCrFeNiX (X = Mo, Ti, W) high entropy alloy coating by red-blue composite laser cladding on copper alloy

In this study, the problem of high reflectivity of copper alloy surface to traditional infrared laser beam was overcome by red-blue composite laser cladding technology. The problem of cracks and other defects caused by the large difference in thermal expansion coefficient between copper substrate and high entropy alloy coating was overcome by electroplating Ni intermediate layer on the surface of copper alloy. A high-entropy alloy coating with tight bonding and no obvious defects was successfully prepared on the surface of copper alloy. The phase composition, microstructure evolution, hardness and tribological properties of high-entropy alloy coatings after adding different elements were studied. The experimental results show that all the CoCrFeNi coatings are FCC phase. After the addition of Mo, Ti and W elements, σ phase rich in Mo and Cr, TiCo2-type Laves phase and Fe7W6-type μ phase appeared in the high entropy alloy coating, respectively. The average microhardness of CoCrFeNiX (X = Mo, Ti, W) high entropy alloy coatings reached 730 HV0.2, 1090 HV0.2 and 378 HV0.2, respectively. The wear rates of CoCrFeNiMo, CoCrFeNiTi and CoCrFeNiW high-entropy alloy coatings were 47.17 %, 90.56 % and 22.64 % lower than those of CoCrFeNi coating, respectively. The wear scars were analyzed by SEM and EDS, and the friction and wear behavior mechanism of CoCrFeNiX (X = Mo, Ti, W) high-entropy alloy coating was investigated. It is mainly composed of abrasive wear, adhesive wear and oxidation wear. The research results provide practical guidance for the preparation of high-entropy alloy coatings on copper surface, and lay a theoretical foundation for laser cladding such high-entropy alloy materials and substrate materials.

Friction and wear behavior of C implanted copper via ion beam-assisted bombardment

This work modified the surface of copper using physical vapor deposition and investigated the wear behavior of the modified copper at low load and sliding speed. The results of the study showed that the adhesion between the thin film prepared using the ion beam deposition technique and the substrate was insufficient, leading to an increased wear rate of copper after surface modification. However, when carbon particles were injected using ion beam-assisted bombardment, the friction properties of copper were significantly improved, with a decrease in wear rate from 1.6 × 10−4 to 8 × 10−6 mm3/N m and a 40% reduction in friction coefficient. This improvement can be attributed to the amorphous carbon layer on the copper surface, as well as the injection of carbon particles into the substrate, which enhanced the adhesion between the film and the substrate. Furthermore, a continuous copper oxide film formed during the friction and wear process, providing lubrication and protection to the substrate in conjunction with the amorphous carbon layer. Additionally, the primary wear mechanism of copper shifted from abrasive and adhesive wear to oxidation wear after ion beam-assisted bombardment with carbon injection. This study provides new insights and methods for material design and engineering applications by investigating the effects of ion beam-assisted bombardment technology on the wear resistance of copper materials.