查看更多>>摘要：? 2021 Elsevier B.V.In this study, the wear evolution and wear mechanism of microstructured diamond abrasive grains in scratching WC/Co were investigated. Surface microstructures with 0° groove arrays, 45° groove arrays, square arrays, rhombus arrays, and wave groove arrays were initially fabricated using a nanosecond pulsed laser without obvious surface damage. The grain wear evolution process, characteristics of the scratching surface, and impact on the specific scratching force were then analysed. The results show that surface microstructuring affects the life extension of the diamond grains, the effectiveness of which can be sorted in the following descending order: square arrays, rhombus arrays, 45° groove arrays, 0° groove arrays, no microstructure, and wave groove arrays. Finally, the wear evolution process of the microstructured diamond grains was identified, which mainly covers adhesion→cracking→micro-fracture of the unit-abrasives→macro-fracture of the unit-abrasives→macro-fracture of the grain→pull-out, and the wear mechanism of the diamond grains was also explored.
查看更多>>摘要：? 2021 Elsevier B.V.Die wear during trimming of advanced high strength steel (AHSS) sheets adversely effects the edge quality of trimmed sheets. Due to the large size of the industrial scale dies, it is difficult to measure the wear at the trim edge of the die inserts as a function of the number of trimming cycles. In this work, an optical surface profilometry method was used to determine sliding wear and impact damage on AISI D2 die inserts used to trim 1.4mm thick DP980 sheets through a semi-industrial scale trimming press. Reduced peak height (Spk) and reduced valley depth (Svk) were determined by establishing the bearing ratio curves in the damaged areas of the trim dies as a function of the number of trimming cycles up to 80,000 cycles. The sliding-induced percentage of total volumetric loss (SPOTV) decreased with the number of trimming cycles on the upper sliding plane revealing that the main damage mechanism changed from sliding-induced wear to impact fracture. The dominant damage mechanism on lower sliding plane was fracture induced as SPOTV on this plane maintained a low and constant value and evidence for chipping was observed on the trim die edge. The performance of trim dies could be improved by increasing the fracture toughness of the lower die and increasing the wear resistance of the upper die by applying proper coatings.
查看更多>>摘要：? 2021 Elsevier B.V.The wear behavior of metallic alloys at variable temperature is a crucial aspect in many industrial components such as turbines and compressors in aircraft engines. In particular, the blade/disk contact is subjected to a cyclic thermal loading combined with a cyclic sliding (fretting) which can significantly damage the interface. The objective of this work is to investigate the behavior of the interface during such variable temperature sliding sequence. Results show that the protective oxide layer (glaze layer) formed at high temperature is destroyed at low temperature within a latency time. However, the high-temperature glaze layer induces a reduction of the wear volume at lower temperature compared to a standard fretting test performed at a fixed temperature condition (without initial glaze layer formation). When the glaze layer is turned into debris, it enriches the debris bed with a high proportion of cobalt element. This high concentration of cobalt element in the third body layer can clarify the lower steady state wear regime compared to an equivalent fixed temperature test condition.
查看更多>>摘要：? 2021 Elsevier B.V.In this paper, experiments were conducted to investigate the penetration characteristics of low-frequency impact of pulsed water jet. The pulsed jet was generated with pulse length of 217 mm at the frequency of 120 Hz, using a round nozzle with diameter of 1 mm within the standoff distance of 40 mm. The macro characteristics (entrance shape, cross-section features, penetration depth, entrance area, and penetration rate), inner wall roughness, and micro morphology of penetration cavity on different targets (sandstone and granite) were measured to investigate the penetration performance and mechanism of low-frequency liquid impact. Results showed that there were two different penetration patterns on different targets based on the macro characteristics and the analysis of flow field loading characteristics in penetration cavity. The penetration cavities were present as funnel-shaped pits with narrow entrance and large depth on sandstone samples, and shallow craters with wide entrance and small depth on the granite samples. The roughness on entrance zone and bottom zone of penetration cavity on sandstone decreased with impact time and impact velocity, and that of middle zone increased. The roughness of cavity wall for granite increased with the expansion of penetration cavity. It was found that the main destruction pattern of sandstone was in the form of intergranular fracture, and transgranular fracture for granite. Radial confined holes were observed on the cavity wall at different depths, and the holes mainly existed along the grains boundary of sandstone, present on the transgranular fracture surface of granite. Based on the study about the macro failure characteristics, roughness, and micro morphology of penetration cavity, it was expected to provide some useful information for the application of penetration technology by low-frequency liquid jet.
查看更多>>摘要：? 2021 Elsevier B.V.Thin films of wear-resistant tungsten carbide were deposited on steel substrates by sputtering of WC with magnetron sputtering in a mixed argon/acetylene atmosphere. Variation of the acetylene supply during the deposition led to the growth of the tungsten carbide films with different excesses of carbon with respect to the stoichiometric WC. Variation of bias voltage influences mainly the [C]/([C]+[W]) ratio and secondary the mechanical properties hardness and Young's modulus. The films are supposed to combine good wear-resistant properties with a low friction under dry conditions. A tribometric analysis of friction and wear shows that an excess of carbon in the hard material layer can reduce the coefficient of friction by up to 40%. However, the volume of wear increased with increasing amount of carbon, while the nanoindentation measurements revealed higher hardness and lower elastic modulus.
查看更多>>摘要：? 2021 Elsevier B.V.Adhesive wear extension in metal fretting contacts was previously related to the partial pressure of oxygen gas in a porous third body layer. Below a threshold value, the surface oxidation is no more possible and adhesive wear prevails in the inner part of the interface. The contact oxygenation concept (COC) allowing the prediction of the dioxygen partial pressure profile was recently simulated for a 2D surface analysis (i.e. 3D contact) using a numerical Advection-Dispersion-Reaction (ADR) approach. In this study, a simple explicit formulation is derived to capture COC response using a 1D surface analysis (i.e. 2D contact hypothesis).
查看更多>>摘要：? 2021 Elsevier B.V.The present study investigates the sliding wear properties of G350 grey cast iron following various spheroidizing annealing durations. The annealed samples were used as pins in sliding wear tests against AISI 4330 discs. Most testing combinations resulted in mild wear with little matrix damage to the cast iron pin or AISI 4330 disc. A transition to severe wear was observed for the highest load and longest annealing times where the overly spheroidized and ferritized cast iron matrix deformed significantly, prohibited beneficial oxidative wear from occurring, and thus damaged its disc counterpart. The depth of subsurface deformation increased with annealing time but not load. Instead, the depth peaked at 4 kg applied load for each condition due to the spallation of the affected surface layer at the higher load.
查看更多>>摘要：? 2021 Elsevier B.V.The combination of texturing pretreatments and lubricant films was researched to improve the dry friction and wear performance of aluminium alloys. Three linear microtextures with different spacings were fabricated on the aluminum alloy substrates by ultrasonic surface rolling processing (USRP). The surface characteristics of different microtextures, such as micromorphologies, hardnesses, and wettability, were tested. PTFE/PPS lubricant films were prepared onto the textured surfaces by electrohydrodynamic atomization (EHDA), and micromorphologies of the films were observed. The friction and wear performance of aluminum alloy substrate and the films with texturing pretreatments were tested by ball-on disk reciprocating sliding dry friction experiments, and the countball material was 316L steel. The test data indicated that all films effectively reduced the friction coefficient of the substrate surface, and among them, the film sample URTC100 with a combination of 100 μm spacing texture and PTFE/PPS film exhibited the best effect of anti-wear while dry reciprocating sliding. Compared to the unpretreated film sample, URTC100 increased the wear life by 10% and reduced the wear track width and adhesion width by 35% and 25%, respectively.
查看更多>>摘要：? 2021The authors regret that we made an error in the equation proposed to describe one of the key processes in fretting, and would like to apologise for any inconvenience caused. The error relates to the equation proposed to describe the transport of oxygen to the active surface to form oxide debris. The main proposal and argument of the paper (namely that of the concept of rate-determining processes in fretting) is not affected by this error. Indeed, in the original paper itself (as highlighted in the abstract), we said: “A number of assumptions have been made in deriving the equations which describe the key processes and it is recognised that these equations themselves may be refined in light of future research; however, any such revised equations can simply replace those proposed as part of the rate-determining process framework.” A new framework which describes the role of three key processes in fretting wear of metals was proposed, with these three processes being: (i) oxygen transport into the contact; (ii) formation of oxide-based wear debris in the contact and (iii) ejection of the wear debris from the contact. To maintain system equilibrium in steady-state fretting, it was argued that these three processes must operate at the same rate as each other (i.e. that debris cannot be ejected from the contact faster than it is formed, and that debris cannot be formed faster than it is ejected). Accordingly, the observed wear rate is the rate of the process with the lowest rate of the three processes, with this process being termed the rate-determining process (RDP). It is noted that two of the three key processes can be classified as transport processes (i.e. transport of oxygen into the contact to form oxide debris and transport of that debris out of the contact). In our original paper, it was proposed that the rates of both transport processes decrease with increasing fretting contact size (i.e. the distance over which transport of the species takes place). There is no general expectation that the dependence of these two rates upon the contact size will be the same and a generalised schematic diagram (Fig. 5) was proposed in the original paper to describe this; this key figure is reproduced here in this corrigendum for clarity.1 It is noted that this is a schematic diagram and is therefore not affected by the error made in the derivation of the equation to describe one of these transport processes. Furthermore, it is argued that the RDP concept proposed is applicable to all fretting contacts, irrespective of whether the contact is conforming or non-conforming, and irrespective of its dimensions and the direction of the fretting motion with respect to those dimensions. [Formula presented] A key assumption in the original paper is that the instantaneous rate of surface recession (wear), summed over the two specimens in the fretting pair, must be the same at all positions within the wear scar at any point in time. It was then argued that this means that the rate of consumption of oxygen required for formation of oxide debris, [Formula presented], will be the same at every point in the contact at a given time. It is noted that [Formula presented] is defined as the consumption rate of oxygen per unit area of contact in the formation of oxide-based debris (with S.I. units of kg m-2 s-1). The error made in the original paper relates to the derivation of the rate equation related to oxygen transport into the contact to form oxide-based wear debris. In the formulation of Equation (A1.8) in Appendix 1 of the original paper, we proposed that the total rate of consumption of oxygen required for debris formation across the whole contact will be directly proportional to the observed time-based rate of wear in the contact. We stand by this proposition; however, we made in an error in the way that this concept was formulated into an equation (we misinterpreted [Formula presented] as being the rate of consumption of oxygen across the whole
查看更多>>摘要：? 2021We conduct in-situ observations of the wear process of metals in dry conditions. To this end, we constructed an experiment to observe the wear process of a point contact area, created between a rotating sapphire disc and a metal pin. The experimental setup included a microscope and a camera with visible-light and near-infrared detectors. Several steels, including stainless steel, and copper alloys were tested as pin materials. The wear comprised plastic flow, formation of transfer layers from the metal pin onto the sapphire disc, and expansion of the contact area. The influences of metal compositions and base metals on the wear behaviour were discussed.
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