查看更多>>摘要：? 2021 Elsevier B.V.A comprehensive investigation was conducted on the tribological properties of micro ball bearings comprised of borosilicate glass balls and polymer guide. Experiments were performed to assess the friction and wear behavior of the micro ball bearings with respect to operating conditions. Also, the effects of guide shape on the rolling resistance of the balls were investigated using FEM simulation. It was found that even under high load conditions the glass/polymer-based micro ball bearings showed a sufficiently low friction coefficient of ～0.028. In addition, 10 million cycle durability test confirmed the excellent wear resistance of the micro ball bearings. Through FEM simulation, it was confirmed that the tribological properties of the micro ball bearings may be further enhanced by using ball guides with a U-groove rather than a V-groove shape. It is expected that the numerical and experimental results presented in this work will aid in development of micro ball bearings that would be useful for various practical applications.
查看更多>>摘要：? 2021 Elsevier B.V.Laser cladding could be applied on railway wheels to improve their service lives. Fe-based alloy powder is widely used as the laser cladding material due to its good self-fluxing ability and low price. However, the friction coefficients and wear rates of Fe-based alloy laser claddings are high. WS2 is used as the additive for common laser cladding treatment, while it has not been used for claddings on railway wheels. Understanding the influence of WS2 concentration on the mechanical and tribological properties of Fe-based alloy laser claddings on railway wheels has significance for extending the application of laser treatment on railway transit. Therefore, laser claddings of Fe-based alloy powders with different contents of WS2 powder (0, 2%, 4%, 6%, 8%) were produced on the railway CL60 wheel material. Rolling-sliding tests were conducted on a twin-disc tribometer using the uncladded and cladded wheel samples against an uncladded U71Mn rail sample. The results indicated that the microstructure of laser claddings was composed of dendritic and eutectic phases. With the increase in the WS2 content from 0 to 6%, the size of dendritic phases was decreased from around 20 μm to less than 10 μm. With 8% WS2, the size of dendritic phases was increased to around 10–20 μm. Laser claddings of Fe-based alloy powders with WS2 included (Fe, Ni) and (Fe, Si) solid solutions, hard carbide (Cr7C3), Ni–Cr–Fe, and CrS phases. The hardness was increased to 730–820 HV0.5 and residual stresses were changed to be compressive state. Rolling contact fatigue (RCF) cracks preferentially initiated and developed along the boundary between dendritic and eutectic phases. The smallest wear rate and shortest RCF cracks occurred on the cladding from powders with 6% WS2. Thus, the optimum content of WS2 in the Fe-based alloy powder was 6% for laser cladding on the railway wheel material.
查看更多>>摘要：? 2021 Elsevier B.V.Developing nano-materials as lubricating anti-wear additives is an effective way to reduce wear and friction of mechanical equipments for significantly improving their energy conservation and service life. Herein, the tribological properties (friction-reduction and wear-resistance properties) friction-reduction and wear-resistance mechanism of 3D graphene nanosheets (GNS), SiO2 nanoparticles and their nanoblend as additives in castor oil at steel/steel (SUS304 stainless steel) contact interface are comprehensively investigated under varied load and speed. And two main wear forms, adhesive wear and abrasive wear, under different experimental conditions are analyzed in detail. The friction and wear of the corresponding friction interface can be effectively reduced by these nano additives, the nanoparticles' mechanism of action is closely related to the load and speed applied, in particular under low speed and heavy load. The SiO2/3D GNS nanoblend demonstrates the best tribological performance with the maximum reduction of reducing wear and friction by 46.1% and 22.4%. By comparison, the tribological performance of pure GNS and SiO2 are much lower than that of the GNS and SiO2 hybrid nanoparticles. The origin of such high anti-wear mechanism is rooted from the formation of the protective film formed by 3D GNS and SiO2 as well as the synergistic effect between 3D GNS and SiO2. Besides, the easy-shear nature between the layers of graphene and the rolling-bear effect of SiO2 together reduce the friction at the steel/steel contact friction interface.
查看更多>>摘要：? 2021 Elsevier B.V.Structural design is a crucial strategy to improve the service performance of amorphous carbon films in aggressive environments. In this study multilayered graphite-like carbon (GLC) films with adhesive layer/gradient interlayer/doping layer architectures with varied gradient interlayer thickness were deposited on 316L stainless steel substrates by closed field unbalanced magnetron sputtering. The effect of gradient interlayer thickness on microstructure, mechanical, tribological and corrosion behavior of the GLC films was investigated. The results show that the mechanical properties and bonding strength decrease with increasing gradient interlayer thickness due to the increased sp2 content, surface roughness and decreased film integrity. The friction coefficient curves in ambient air and 3.5% NaCl solution show similar three-stage feature with distinctive wear mechanism in stage III. The decreased mechanical properties and loose microstructure of GLC films with thicker gradient interlayer thickness caused the decreased wear resistance in both ambient air and NaCl solution. In comparison with the uncoated substrate, the GLC films show improved corrosion resistance in NaCl solution, which also decreases with the increased gradient interlayer thickness due to the low film compactness and high electrical conductivity.
查看更多>>摘要：? 2021 Elsevier B.V.In today's manufacturing, selective laser melting (SLM) enables the production of 3D metal parts with innovative designs. However, this technique is still limited to certain materials due to residual stresses and cracking. The ultra-low carbon maraging steel 18Ni300 is a proven steel for SLM processing, while H13 steel still presents some challenges due to cracking and low wettability. These two steels are currently used in mould making due to their mechanical properties. Aiming to compare and better understand the behaviour of these two steels manufactured by selective laser melting, their mechanical performance and dry sliding wear were investigated. Both steels processed by SLM exhibited the expected yield stress and tensile strength values, suitable for mould making. Dry sliding wear tests performed using a pin-on-disc apparatus, where pins of steel were pressed against discs of polypropylene reinforced with 40 wt% short E-glass fibres, showed that the H13 steel had a specific wear rate two orders of magnitude lower than the 18Ni300 steel (0.11 × 10-7 mm3/m.N). The wear mechanism of the 18Ni300 steel is abrasion, while fatigue plays the main role in the H13 steel. The results of this work allow to establish a correlation between the obtained microstructure, mechanical behaviour and tribological performance of both steels under the tested conditions and show that the H13 steel, processed by SLM, can be a good choice for the critical zones of moulds where a higher wear resistance is required.
查看更多>>摘要：? 2021 Elsevier B.V.A low-cost Co-based alloy was employed to fabricate friction stir welding (FSW) tools to weld TA5 alloy under different welding speeds. The tool wear characteristics, tool degradation mechanisms and effects of tool wear behavior on the microstructure and mechanical properties of joints were investigated in detail. Results reveal that the heat input near weld root decreases with the increase of welding speed and the tool wears more extensively under lower heat input when the deterioration rates of tool sizes are considered. Furthermore, the tool wears out mainly by mechanical abrasion near pin tip, leading to a large number of tool particles in mixed regions accompanied by severe material loss. The tool wears less severely near pin root and shoulder, since the adhesion layer caused by adhesive and diffusional wear mechanisms is the main cross-sectional wear morphology, and the interlayer rich in W and Cr between adhesion layer and intact part of tool may protect the tool from serious diffusional wear. The foreign β-stable tool compositions were introduced to the weld, reducing the transus temperature. Therefore, transformed acicular α and retained β phases were detected in contaminated zone (CZ) inside stir zone (SZ) compared with the untransformed equiaxed α grains in non-contaminated zone (NCZ). In addition, the acicular α and β phases result in much higher strength and microhardness than base material (BM).
查看更多>>摘要：? 2021 Elsevier B.V.Although the anti-friction and wear resistant technology in dry condition between friction contacts has attracted widespread attention, it has limitations because of the challenges associated with the solid lubricant. A strategy is herein presented using a Cu@Graphite solid lubricant in the reduction of friction and wear in dry condition. The tribological tests were carried out at three sliding speeds (0.1 m/s, 0.3 m/s and 0.5 m/s) at room temperature with a ball-on-block contact. The graphite in the Cu@Graphite solid lubricant plays a key role in separating the contact pair to decrease the adhesion, which decreases the coefficient of friction (COF). Moreover, the copper in the Cu@Graphite solid lubricant can be transformed to the contact pair and then fill in the micro-defects and tiny scratches, which repairs the friction pair. The COF between the friction pair decreased >400% and the wear volume decreased sharply when the Cu@Graphite solid lubricant was introduced in the interface of the friction pair. In addition, the study develops a promising application prospect of the hybrid composite material, not only as a solid lubricant, but also as a repairing additive.
查看更多>>摘要：? 2021 Elsevier B.V.Given an incomplete combustion of fuel, soot particles commonly exist in the engine lubrication system and are detrimental to the normal operation of the lubrication system. A new method to suppress the effect of soot particles was proposed in the present study. Magnetic MoS2 (M ? MoS2) composite was prepared, and its tribological performance in polyalphaolefin (PAO) 6 mixed with biodiesel soot (BDS) particles were investigated. Furthermore, the tribological behavior of M ? MoS2 in PAO 6 containing BDS with and without magnetic field were compared. The test results showed that the adding M ? MoS2 alone was ineffective in reducing the soot-induced wear, whereas the wear was significantly reduced after applying an external magnetic field. The synergistic repair mechanism of M ? MoS2 composites and a magnetic field on mitigating wear caused by BDS was analyzed by employing a series of surface characterizations.
查看更多>>摘要：? 2021 Elsevier B.V.The influence of rotating particles on surface damage should be considered to improve the accuracy of erosion prediction. In the present study, numerical simulations were carried out to investigate the wear morphology and stress distribution of a target material subjected to rotating particle impacts. A new experimental method was established to validate the model. The model was then used to study the influence of rotating particle impacts at different impact velocities and angles on wear behavior of the material. Correlation between the severity impact wear and particle rotation was observed and quantified. The results show that rotation of solid particles impacting a material can significantly affect the magnitude and pattern of impact wear. Particles with a forward spin were found to promote forward movement of the material surface, whereas particles with a backward spin contributed to vertical deformation of the material. Finally, impact wear profiles produced by different particles with different rotation modes were compared. These results provide insights into the damage mechanism of rotating particles and a theoretical basis for further investigations.
查看更多>>摘要：? 2021 Elsevier B.V.The diamond wire sawing is superior for the wafers manufacturing in the photovoltaic and semiconductor industry. In this research, analytical models were emphasized and experiments were designed to describe the surface formation, wire marks formation and crack generation in diamond wire sawing (DWS). It was found that wire marks are mainly caused by the wire bow and the wire lateral motion. The width of the wire marks are alternately difference due to the reciprocating sawing and wire bow. The twisting effect of wire was introduced as a composition of surface formation. Chips are removed by abrasive grains, and residual material left forms sawn surface. Surface roughness was investigated regarding the combination of wire marks and sawn surface. It was found that roughness changes with the feeding position and wire motion. Wire number that forming the wire web has influence on the sawing quality. It was found that increasing of wire number was useful for improving roughness as the stiffness of wire web is enhanced. The wafer surface was observed by Scanning Electron Microscope (SEM) and 3D profiler to analysis the geometric characteristics of wire mark and wafer deformation. It was found the wire mark in the contact zone was related to the sawing direction and action force. Furthermore, the surface defects was analyzed on the aspect of bearing rate. Wafer surface profile of long-term deformation after stress relief was observed.
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