Wear Scars Research Articles

Aluminum and alumina/MoS2/cellulose derivative composite: design and performance

Nanoparticles were added to improve the tribological performance of the biopolymer-based composite films. Aluminum and alumina were used as additives. The matrix of the composite was MoS2/hydroxypropyl methylcellulose (HPMC). The ternary additive/MoS2/HPMC hybrid composites were successfully prepared via solvent evaporation. The surface morphology, thickness, microstructure, and wear scars were analyzed using scanning electron microscopy. X-ray diffraction was used to analyze the crystal structures of the nanoparticles in the composite films. Finally, a wear test was conducted to determine the tribology behavior and was discussed using the third-body theory. Because of the high surface-area-to-volume ratio of the additives, nanoparticles were exposed and densely distributed on the composite surface. Disclosed nanoparticles caused peaks and valleys and showed more significant undulations, prompting a highly rough surface. The addition of nanoparticles enhanced the load capacity of the composite films by 155%. In the meantime, nanoparticle additives significantly reduced the coefficient of friction by 50% and improved anti-wear performance by five times. The nanoparticles in the wear scar exhibited an excellent third-body mechanism during the wear process, coordinating the velocity accommodation mode between the two rubbing surfaces and the transfer load.

Long-Term Lubricity of Carbon Nanoparticle Coatings on Periodically Laser-Patterned Metallic Surfaces

The lubricity of coatings made from different types of carbon nanoparticles such as carbon onions, carbon nanohorns and carbon nanotubes is investigated on line-patterned AISI 304 stainless-steel substrates using ball-on-disc tribometry over 200,000 sliding cycles. Picosecond direct laser interference patterning is used to create line-patterns on the substrate surfaces which are subsequently coated by electrophoretic deposition. Friction testing is conducted on as-processed surfaces in linear reciprocal mode at a normal load of 100 mN with alumina and 100Cr6 as counter body materials. The resulting wear tracks on the substrates as well as wear scars on the counter bodies are characterized by scanning electron microscopy as well as energy-dispersive X-ray spectroscopy. Tribometry shows that CNTs have the ability to maintain lubricity against both counter body materials. CO and CNH coatings sustain their lubricity against 100Cr6 over the full test duration but fail against alumina. In contrast to alumina, substantial carbon transfer from the substrate surface to 100Cr6 counter body is observed.

Tribological performances of a-C films tested on dry nitrogen environment with various Hertz pressures: Failure mechanisms and in-situ formation graphene

The tribological properties of hydrogen-free amorphous carbon (a-C) films are affected by the test environment and load condition. The wear mechanisms of a-C films sliding against Si3N4 ball under inert atmosphere exhibits different mode during different sliding cycles. The results show that the tribological behaviors for a-C films exhibit adhesive wear and it did not wear out even after sliding test 40,000 cycles when the normal load is 1 N. As the normal load increases, the wear mechanisms mainly show fatigue wear and three-body wear induced by fatigue wears due to the increasing of alternating stress. The emergence of three-body wear will drastically change the local stress distribution of a-C film. The position obtaining maximum Von-Mises stress shifts from the subsurface of substrate to subsurface of a-C film, and the maximum Von-Mises stress and Hertzian contact pressure increases sharply. The structures of in-situ formation graphene originated from the transformation of amorphous carbonaceous structure are detected on the wear scars. The formation of carbonaceous transfer film is beneficial to facilitate the graphitization transition with increasing Hertz pressure from 0.65 GPa to 1.35 GPa. On the other hand, the transition temperature of graphitization is sharply reduced to the flash temperature of contact zone due to the emergence of three-body wear obtaining the instantaneous Hertz pressure reached to 29.5 GPa. These conclusions possibly provide valuable references for designing film thicknesses, reveal tribological mechanism for a-C films under dry inertness atmosphere and broaden industrial application.

Elaboration of Ionic Liquids on the Anti-Wear Performance of the Reinforced Steel-Steel Contact Surface

This study conducted a tribological investigation of base oil (PAO6 and 5W 40) and ionic liquids (IL)-modified lubricants through a four-ball tribometer for 30 min. The lubricants were fabricated via a two-step method using stirring magnetic and ultrasonic dispersion. IL, base oil, and lubricants were, respectively, characterized by XRD and FTIR analysis. In addition, multiple characterizations such as EDS, 3D morphology, and SEM were carried out to evaluate the wear and friction performance of steel balls. Ultimately, the results showed that the coefficient of friction (COF) and wear scar diameter (WSD) of wear scar lubricated by IL-modified lubricants were greatly decreased than that by base oil. IL can well improve the tribological properties of PAO 6 oil and 5W-40 oil due to the tribo-film appearance on the friction surface of wear scar by the effective role of IL. Fascinatingly, this investigation comprehensively and elaborately put a new sight into the lubrication mechanism of how IL reacted with a base oil and enhanced the tribological characteristics.

Effect of temperature on tribo-corrosion behaviors of parallel steel wires of main cable in the suspension bridge

The effect of temperature on tribo-corrosion behaviors of parallel steel wires of main cable in the suspension bridge was investigated in the present study. The self-made tribo-corrosion test rig was employed to conduct tribo-corrosion tests of parallel steel wires in 3.5% (wt%) NaCl solution and deionized water with distinct temperature. The coefficient of friction, wear loss and wear coefficient of steel wires were presented. Morphologies and chemical elements of wear scars of steel wires were measured by the scanning electron microscope and electron spectrometer, respectively, in order to explore wear mechanisms of steel wires. Tafel polarization curves, Nyquist diagram and equivalent circuit diagram were obtained by the electrochemical analyzer to investigate electrochemical corrosion behaviors of steel wires. Finally, the interaction between corrosion and wear of steel wires were quantitatively demonstrated. The results show that the coefficient of friction, wear volume and wear coefficient of parallel steel wires all increase with increasing temperature in cases of deionized water and 3.5% NaCl solution. Wear mechanisms of parallel steel wires are adhesive wear, abrasive wear and corrosive wear in the 3.5% NaCl solution as compared to adhesive wear and abrasive wear in the deionized water. An increase of temperature reduces the corrosion resistance of parallel steel wires in the 3.5% NaCl solution, while the interaction of corrosion and wear increases with increasing temperature indicating the synergistic effect. The results are of important fundamental significance to the load-bearing safety of main cable and improvement of service stability of suspension bridge.

Influence of Carbon Nanotubes on Enhancement of Sliding Wear Resistance of Plasma-Sprayed Yttria-Stabilised Zirconia Coatings

An experimental investigation was performed to study the performance of thermally sprayed yttria stabilised zirconia (YSZ) coatings obtained with the reinforcement of carbon nanotubes (CNTs) in different weight percentage proportions. The atmospheric plasma spray (APS) method was used to deposit YSZ + CNTs at three different weight proportions on low carbon steel (AISI 1020) following the industrial standard procedure. The quality of thermally sprayed coatings was evaluated to report on percentage porosity (ASTM B276), sliding wear resistance (ASTM G133-05), and metallurgical bonding of the coating with the substrate material. From this investigation results, it has been confirmed that the thickness of the coatings is almost uniform, and the percentage porosity is decreased with an increase in CNTs weight percentage proportion. ImageJ software has confirmed the presence of CNTs in the ceramic deposit, and also uniform distribution throughout the coating. Subsequently, the metallurgical bonding of the deposit is also ensured and confirmed that the deposit adheres on the substrate. The hardness of the coating found increased with the increase in CNTs proportion as 554 Hv with 1 wt.% CNTs, 805 Hv with 3 wt.% CNTs, and 933 Hv with 5 wt.% CNTs in thermally sprayed YSZ. The results obtained are highly appreciable when compared to the hardness (454 Hv) of thermally sprayed pure YSZ coating. From results of wear tests, it was found that at slow speed (i.e., 319 rpm), the minimum mass loss was identified for all the three different combinations of CNTs reinforced coatings. However, 5 wt.% of CNTs in YSZ has very minimum wear at 5 kgf load and subsequently mass loss increased with the decrease in CNTs weight percentage proportion. Based on wear resistance, it was found that the 5 wt.% CNTs in YSZ has a maximum wear resistance. Severe wear scars and coating delamination in 1% CNTs reinforced coatings were identified from the microstructural analysis. Therefore, addition of CNTs in YSZ coatings has a significant impact over the wear resistance and mechanical properties improvement of the coatings.

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Study on Microstructure and Properties of NM500/Q345 Clad Plates at Different Austenitization Temperatures

In this paper, the change in the mechanical properties of a composite plate was studied using the heat treatment method, and it was found that the performance of the composite plate was greatly improved under the process of quenching at 900 °C and tempering at 200 °C. The hot-rolled NM500/Q345 clad plates were subjected to heat treatment tests of 860 °C, 900 °C, and 940 °C austenitization + 200 tempering. With the help of an optical microscope, scanning electron microscope, EBSD, and transmission electron microscope, the microstructure, interface element distribution, and defect composition at the composite bonding interface of hot rolling and heat treatment were analyzed. An analysis and friction and wear tests were carried out on the wear resistance of the clad NM500. It was found that the microstructure of the NM500/Q345 clad plate before austenitization was mainly pearlite and ferrite, and both were transformed into lath martensite after austenitization. As the austenitization temperature increased, the size of the martensitic lath bundle also became coarse. After austenitization at 900 °C and tempering at 200 °C, the lath-like martensite structure of NM500 contained high-density dislocations between the laths. With the increase in the austenitization temperature, the surface Rockwell hardness showed a trend of first increasing and then decreasing. The wear was the worst when the material was not quenched. When the clad plate was quenched at 900 °C and tempered at 200 °C, the wear of NM500 was the lightest; the maximum depth of the wear scar was 14 μm; the width was the narrowest, 0.73 mm; and the wear volume was the smallest, 0.0305 mm3.

The fatigue fracture mechanism of Al7075 aluminum alloy clinching joints

Lightweight aluminum alloys are widely used in automotive structural parts. Clinching (press-joining) is one of the most promising alternatives to welding for joining aluminum alloys, and as the failure of the joint is mainly caused by fatigue, the fatigue properties of the clinched joints directly affect the reliability and safety of the connected specimens. To gain a deeper understanding of this phenomenon, the static mechanical and fatigue properties of Al7075 aluminum alloy single-lap clinched joints were studied using static strength and tensile-tensile fatigue tests. The F–N curves of the joints were fitted using a straight-line and three-parameter power function method. The fractured samples and wear scars were analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The results showed that the neck of the clinched joint and the upper sheet near the joint experienced the highest degree of fatigue fracture, the fretting wear debris consisted mainly of alumina and metallic aluminum, and the fretting wear was of a mode that differed from the two modes identified in the literature that we have dubbed “upper sheet inter-sheet region fretting wear.”

The Effect of the Displacement Amplitude on the Fretting Wear of GCr15 Steel with a TiC Coating.

In the present paper, the effect of mechanical ball milling time on the fretting wear of GCr15 steel balls at different displacement amplitudes is investigated. TiC powder coating was fabricated on the surface of GCr15 steel balls using various process times, and the fretting wear tests were conducted on an AISI 52100 steel disk with the applied force of 80 N. Additionally, various displacement amplitudes (10 μm, 20 μm, and 60 μm) were selected. Specimen attributes and wear scars were characterized using an inverted metallographic microscope, a microhardness tester, an X-ray diffractometry analyzer, a white light interferometer, and a scanning electron microscope. The results showed that thick and continuous coatings could be obtained at the milling time of 18 h. The specimens processed for a longer milling time demonstrated better fretting wear resistance, which we attribute to higher microhardness of the surface layer. The coefficient of friction and wear volume of specimens at each different displacement amplitude significantly decreased with increasing milling time. As the displacement amplitude increased, the three fretting states were: partial slip coordinated by elastic deformation; partial slip state coordinated by plastic deformation; and gross slip condition. Our observations indicate that mechanical ball milling could be an efficient approach to improve the fretting wear resistance of GCr15 steel balls.

High temperature abradable sealing coating for SiCf/SiC ceramic matrix composites

A study of porous YSZ abradable sealing coating (ASC) plasma-sprayed onto SiCf/SiC ceramic matrix composites (CMC) through the compatibility of intermediate layers is reported. The multilayer Si/Yb2Si2O7/LaMgAl11O19 thermal-environmental barrier coating (T-EBC) is served as intermediate layers in consideration of its ability to protect the CMC from recession and ease the misfit of the thermal expansivity. Isothermal exposure and thermal shock tests were conducted at 1200°C and led to the decomposition of t'-ZrO2 phase to t-ZrO2 and c-ZrO2 phases in YSZ topcoat, the formation of mud-cracks throughout the entire coating structure and thermally grown oxide (SiO2), with following an Yb2Si2O7 reaction layer. The measured bond strength of the coated samples was 5.47 ± 0.85 MPa, and the fracture position mainly happened inside the CMC substrate. The Superficial Rockwell Hardness (HR15Y) considered to be an important factor in abradability increased by only 1.34% after 1200°C isothermal exposure for 100 h, showing excellent high temperature hardness stability. The abradability of the ASC was investigated by a sliding wear test, the fatigue wear mainly occurred in worn scar when encountering Si3N4 ceramic ball with high hardness and low thermal conductivity, while adhesive wear occurred when GCr15 steel ball with low hardness and high thermal conductivity are encountered.

Mechanism of low friction coefficient of carbide ceramics and carbon-containing steels

To investigate frictional properties of carbide ceramics and carbon-containing steels reciprocating friction experiments were conducted in air. For these experiments, SiC, WC, TiC, and TiCN were used as carbides. Also, Al2O3, Si3N4, TiN, and TiAlN were used as non-carbides. In addition, experiments were conducted using three types of steel as plate materials: JIS SKH4 (carbon content 0.73–0.83%), JIS SUS430 (carbon content lower than 0.12%), and JIS 312L (carbon content lower than 0.02%). As a result of the experiment, a low coefficient of friction was obtained for all combinations of identical carbides. After the friction experiment, the wear debris adhering around the wear scar was analyzed by Raman spectroscopy. As a result, it was found that the wear debris of all carbide ceramics showing a low coefficient of friction contained a graphite-like material. These results demonstrated that a graphite-like material is generated by friction between identical carbide ceramics, as in the case of carbon-based materials such as diamond and DLC. In friction between ceramic balls and steels, the SKH4 plate showed a low coefficient of friction similar to that produced by friction between identical carbides. Raman spectroscopy revealed that the SKH4 plate wear debris contained a large amount of graphite-like materials, while the SUS430 plate wear debris, which showed a high coefficient of friction, contained only a small amount. Moreover, SUS430 showed stronger adhesion to the friction surface than SKH4 did, probably because the graphite-like material generated by friction reduces metal adhesion. These results demonstrated that carbon in steel also produces a graphite-like material by friction, and demonstrated that it lowers the friction coefficient by reducing the shear force and by suppressing adhesion.

Conductivity and tribological properties of IL-PANI/WS2 composite material in lithium complex grease

An ionic liquid-polyaniline/tungsten disulfide (IL-PANI/WS2) composite was synthesized in 1-butyl-3-methylimidazole tetrafluoroborate (LB104) aqueous solution by in-situ polymerization and characterized by Fourier transform infrared spectroscopy. A current-carrying friction and wear tester was used to study the tribological properties of steel—steel and copper—copper friction pairs lubricated by an IL-PANI/WS2 lithium complex grease (LCG). After the experiment, scanning electron microscope was used to observe the surface morphology of the wear scar on the steel and copper plates, and X-ray photoelectron spectrometer was used to analyze the elemental composition of the wear scar surface. The results show that compared with greases containing IL-PANI and WS2, greases containing IL-PANI/WS2 exhibit better antiwear performance when lubricating steel—steel friction pairs and better tribological performance and electrical conductivity when lubricating copper—copper friction pairs. Therefore, it can be concluded that WS2 and IL-PANI have a synergistic effect.

Effects of Al, Ti, and Cr content with different interlayer configurations on tribological behavior of AlCrN and AlTiN multilayer coatings

In this study, AlCrN and AlTiN coatings with various interlayer numbers and compositions were deposited on AISI D2 cold work tool steels using cathodic arc-physical vapor deposition to enhance the adhesive and abrasive wear resistance of cold forming tools. Linear reciprocating tribometer experiments were conducted at 15 and 30 N loads under dry sliding conditions to evaluate the wear resistance and friction characteristics of these coatings. The coatings were chemically and morphologically characterized using an optical microscope, an atomic force microscope, a scanning electron microscope equipped with energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis. Wear scars were examined with an optical profilometer after the tribometer tests to determine wear volumes and wear mechanisms. The results showed that AlTiN coating with six interlayers could be a cold work steel coating with nearly 6 times lower wear rate compared to AlCrN coatings at 3.1 GPa contact pressures.

Activated Carbon Nano-Particles from Recycled Polymers Waste as a Novel Nano-Additive to Grease Lubrication

A worldwide growing trend is dedicated towards reducing carbon dioxide emissions from mechanical systems in different industries. One key factor under focus of research is to decrease energy losses in rotating machinery during operation by improving lubrication performance. This paper presents a novel grease nano-additive using activated carbon (AC) as a byproduct from recycled polymer waste. Five different concentrations of AC nanoparticles (ACNPs) are added to lithium grease to obtain blends containing 0.025 wt.%, 0.05 wt.%, 0.1 wt.%, 0.5 wt.%, and 1 wt.%. The tribological assessment of blends has been performed using a four-ball wear test and load carrying capacity test. The obtained results for blends are compared to samples of base grease and to blends with 2 wt.% reduced graphene oxide (rGO). Test results showed a remarkable enhancement of load carrying capacity of AC samples by 20–30% as compared to base grease. By observing wear scar in rolling elements, the ACNPs lowered the average wear scar diameter (WSD) for all samples by 30–36%. Base grease samples showed the highest coefficient of friction (COF) values between 0.15 and 0.17. These values are reduced to 0.03 and 0.06 for grease with ACNPs reaching their minimum in the case of 1 wt.% AC. These outcomes are found consistent with the enhancements in driving power saving values. The results proved the competitiveness and suitability of the AC as a recycled waste and nano-additive for improving the tribological performance of grease lubrication.

Study on friction properties of different abrasive materials and polylactic acid materials

In recent years, 3D printing technology is often used in various fields such as industry, medical care, and academia, because it can produce components with complex shapes at a lower cost than traditional processing. However, the size of 3D products is often limited by the printable range of printing equipment, so large objects often need to be disassembled and printed before joining. Friction stir welding is used to join different thermoplastics and has considerable potential for industrial applications, and the influence of the design of the welding tool on the formation of the welding zone is an important key. In this study, different abrasive materials and polylactic acid materials were used for friction, and the changes of friction coefficient and friction temperature during the friction process were discussed. The experimental results show the surface roughness of the abrasive tool has a significant effect on the coefficient of friction and temperature rise. As increasing the roughness of the abrasive tool, the wear scars, the cracks below the wear scar are both significant. It can be inferred from the crack shape that the PLA softens at high temperatures and then solidifies again, so the cracks are seen with a streamlined appearance, which means that the softened PLA can be carried by the abrasives tool with highly rough surfaces.

Characterization of the microstructure and self-lubrication properties of a AlCoCrFeNi2.1 eutectic high-entropy alloy with powder-pack boronizing

The as-cast AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) has high fracture strength and ductility, which displays an excellent application prospect in key structural materials. However, its low surface hardness and poor wear resistance at room temperature limit the actual applications in tribology. Here we showed the enhancement of surface strengthening and self-lubrication properties of AlCoCrFeNi2.1 EHEA by a powder-pack boronizing treatment. SEM and XRD analysis indicate that a double affected layer with a thickness of about 42 μm was formed on the surface at 900 °C for 4 h, which were mainly consisted of Ni2Si and FeB. The surface hardness of the alloy was significantly increased from 396 HV to 1108 HV after the treatment. Tribological results show a remarkable self-lubrication property of the boronized EHEA. The friction coefficient of boronized EHEA under the water condition was reduced by 21%, and the corresponding wear volume was decreased by 65%. EDS and XPS analysis demonstrate the formation of silicon/boron-containing tribofilm on the wear scar, which benefits in the achievement of self-lubrication properties with friction and wear reduction under the water condition. Our research provides a general strategy with the powder-pack boronizing method to strengthen AlCoCrFeNi2.1 EHEA and enhance self-lubrication properties, which would certainly boost its industry application.

Microstructure and mechanical properties of composite strengthened high-chromium cast iron by laser quenching and laser shock peening

The study investigated the microstructure and mechanical properties of composite strengthened high-chromium cast iron by laser quenching and laser shock peening. Observation of microstructure, measurement of microhardness, residual stress and FWHM (full width at half maximum), impact toughness and wear tests were carried out on untreated, laser quenched, laser quench-laser shock peened high-chromium cast iron specimens. The research results showed that the laser shock peening will not produce new phases in high-chromium cast iron, and can further promote the transformation of retained austenite into martensite. The grains inside the laser quench-laser shock peened sample were obviously refined, and the carbides were uniformly dispersed. The laser quench-laser shock peened specimen produced large residual compressive stress and FWHM value on the surface, reaching −432.49 MPa and 2.124°, respectively. The problem of residual stress difference between the hardened zone and the transition zone caused by laser quenching was eliminated, and the tensile stress was all converted into compressive stress, which further increases the dislocation density and improves the micro-hardness. The impact toughness value of laser quench-laser shock peened specimen was 4.43 J/cm2, which was 16.27% higher than that of the untreated sample. The friction coefficient and wear rate were significantly reduced, and the wear scar was shallow and narrow, showing weak abrasive wear and oxidative wear, the impact toughness and wear resistance of high-chromium cast iron were improved. The results obtained from this study could be used as reference in future research and applications of laser strengthened high-chromium cast iron.

Design and characterization of AlNbMoTaCux high entropy alloys laser cladding coatings

AlNbMoTaCux high entropy alloy coatings was successfully synthesized on Ti6Al4V through laser cladding. The formation, microstructure characterization, micro-hardness, fracture toughness and wear resistance of coatings with different copper addition were investigated. The results show that porosity and crack defects could be suppressed through the addition of copper. The coatings are mainly consists of BCC structure phase enrichment of Mo, Nb, Ta, HCP structure phase enrichment of Al, Nb, Cu, Ti and FCC structure phase with AlCu2Ti(Fm-3m). Moreover, as the amount addition of copper increases, BCC structure phase decreases and FCC structure increases, and toughness of the coatings are improved obviously, while the micro-hardness is decreased simultaneously. The wear resistance of AlNbMoTaCu0 coating is slightly improved 1.6 times than that of the substrate, while the AlNbMoTaCu0.4 coatings exhibit excellent wear resistance, which is almost 22 times than that of the substrate. Moreover, with the increase of the amount of copper, wear resistance of the coating decreased slightly, and the amount of spalling zone increased in the wear scars.

Microstructure and high temperature tribological behaviour of self-lubricating Ti-TiBx composite doped with Ni[sbnd]Bi

It is a well-established fact, that the tribological performance of titanium and its alloys at high temperatures is poor, especially for self-mated titanium‑titanium pairs. Previous work has shown a significant improvement in mechanical and high temperature tribological behaviour (700–900 °C) for pure Ti sintered with TiB2 ceramic, occasioned by the in-situ formed boric acid lubricant. The current work explores the possibility to extend the lubrication temperature range (below 700 °C) of Ti-TiB2 composites through the incorporation of a nickel‑bismuth mixture (NiBi) as a solid lubricant using laser melting. To this end, phase equilibrium diagrams have been calculated for the Ti-B-NiBi quaternary system using the CALPHAD method to evaluate the possibility of the formation of different phases due to dilution between the substrate and deposit, as well as their possible interactions. The self-lubricating NiBi samples feature a formation of Bi-Ni-Ti-TiBx functional surface. The functional surface demonstrates a compact and unique microstructure of a hard B-rich phase encapsulated inside a lubricous Bi-rich phase. A two-fold increase in hardness of the surface in comparison to the underlying substrate was noted for NiBi laser-melted samples. Further, the NiBi samples were studied under a reciprocating sliding configuration against a Ti-alloy flat-pin counterbody at temperatures including RT, 400 and 600 °C. The resulting wear scars were analysed utilizing SEM, XRD and 3D profilometry to understand the prevalent wear mechanisms. A significant decrease in coefficient of friction and wear rate was observed for the NiBi laser-melted samples sliding at 400 °C and 600 °C due to the formation of a self-lubricating tribo-oxide layer rich in Bi-compounds. The results are reported in comparison to the unmodified reference Ti-TiB2 composite.