查看更多>>摘要：The fretting corrosion behavior of zirconium (Zr) alloy under different pH conditions was investigated. The morphology, microstructure, and wear mechanism of Zr alloy under different pH condition was analyzed. The results indicate that the wear scar Zr alloy in acid condition presents a typical feature of wear debris, furrow, and delamination, indicating that the wear mechanism is oxidation wear and abrasive wear. The microstructure beneath the wear scar is composed of a thick wear debris layer (WDL), deformation layer (DL), and thin tri-bologically transformed structure (TTS). The WDL is a nano-sized grainy structure and the micro-crack is mainly formed on the interface of WDL and TTS. The largest wear volume belongs to the wear scar in pH of 1 condition. Because the corrosion and corrosion induced by wear would destroy the surface protective film and form a thick WDL, which is easy to separate to increase the material loss volume. The Zr alloy in pH of 1 condition shows the largest volume ratio of wear induced by corrosion and corrosion induced by wear.
查看更多>>摘要：The addition of a small selection of nano-sized fillers (e.g., α-alumina) could cause a 1000 × run-in induced wear rate reduction to the otherwise high wear polytetrafluoroethylene (PTFE). The exceedingly high wear rate reduction is strongly related to the formation of an adherent and protective transfer film at the sliding coun-terface; whereas certain aspects of its formation mechanisms remain unclear. Regular wear tests, tribofilm surface nanoindentations, single-stroke polymer debris collection experiments and a special 'stripe test' were conducted in this study. Results found 1) the run-in induced wear reduction is dominated by the polymer wear surface and accompanied by substantially reduced debris size, increased tribofilm hardness, modulus, roughness and work of adhesion against a silicon probe, 2) after the run-in, the volumetric percentage of loose debris retention on the counterface (the retention ratio) decreased monotonically with increased transfer film roughness. A simple adhesive wear model based on Rabinowicz's theory of loose debris transfer was proposed which predicts the debris retention ratio as a function of the polymer wear surface adhesiveness, hardness, modulus and the equivalent interfacial roughness. The model is supported by a strong linear relation between measured debris retention ratio and interfacial roughness (1/S_q).
查看更多>>摘要：Cr, a promising abrasion component, has been introduced into Cu metal matrix composites (Cu-MMCs) to improve their high-energy braking performance. The Cu-Cr interfacial characteristics, worn surface/subsurface morphologies, and effect of Cr on the high energy braking behaviors of Cu-MMCs were measured in this study. The results indicate that an increase in Cr content prevented severe surface plastic deformation (0-5 vol. % Cr) and promoted the formation of mechanical mixed layer (MML) (15-20 vol % Cr), facilitated the improvement of wear resistance and the coefficient of friction, and reduced the thermal fade of composites. The main wear mechanism of the Cu-MMCs changed from adhesion (0-10 vol % Cr) or abrasion (10-20 vol % Cr) to delami-nation or mechanical mixing with an increase in braking energy density (BED). A series of corresponding friction, wear, and wear mechanism maps were established, which revealed the variation in the wear mechanism with the Cr content and BED.
查看更多>>摘要：In efforts to improve the tribological properties of the Ti-Zr alloy, thermal oxidization (TO) and laser surface texturing (LST) were performed on the surfaces of the alloy. Four kinds of samples, i.e., TO combined LST (TOLST), TO without LST (TO-only), LST without TO (LST-only) and annealed-only (Contrast) samples were prepared. The tribological properties of the samples were investigated by carrying out sliding wear tests under starved lubrication using a ball-on-disc tribometer. The results show that TO treatment significantly improves the tribological properties of the surfaces due to the formation of the ZrTiO_4 layer which has a higher hardness and better wettability with PAO_4 oil. More interestingly, the synergistic effect of TO-layer and LST can further improve the tribological properties since the dimple-textures can exist for a long time and offer effective lubrication for the contract areas.
查看更多>>摘要：Anodic oxidation films (AOF) are prepared by a chromic acid process on a rolled surface (AOF-r) and a polished surface (AOF-p) of an Al-Li alloy. Surface topographies are featured as valleys and plateaus with dimples on AOF-r while plain with dimples and scratch marks on AOF-p. In flooded ionic liquid, AOF-r has better tribological property than AOF-p under heavy loads, which is determined by the bearing characteristic (Rpk, Rk, Rvk, and MR1). In addition, dimple on plateau of AOF-r is effective surface texture for increasing load-carrying capacity. In starved ionic liquid, AOF-p has better tribological property than AOF-r because the amount of lubricant engaged in sliding on AOF-p is higher than that on AOF-r.
查看更多>>摘要：Carbon nanotube (CNT) reinforced 316L stainless steel (SS) composites were fabricated by laser powder bed fusion (LPBF) additive manufacturing (AM). This study focuses on microstructure evolution, hardness, and wear behavior. The wear behavior for AM 316L SS and 1 wt% CNT/316L SS was studied by a dry sliding test under normal loads of 10, 15, and 25 N. The addition of CNT to 316L SS led to the change of solidification mode from cellular/columnar to dendritic growth, producing grain refinement. Nanoscale dendrites were observed. Although TEM characterization confirmed the existence of CNT in cell interior, most CNT were damaged, resulting in carbon material segregation along cellular/dendritic boundaries. The wear rate was found dramatically decreased due to the improved hardness. Compared to the adhesive and abrasive wear in AM 316L SS, the wear mechanism of CNT/316L composite was adhesion and oxidative wear. Enhanced cellular/dendritic boundary strengthening by carbon segregation was the main strengthening mechanism of CNT/316L composite.
Ilare BordeasuEduard RiemschneiderIon Dragos UtuCorneliu Marius Craciunescu...
10页
查看更多>>摘要：The paper analyses the effect of the surface microstructure effects on the cavitation erosion following rapid remelting and solidification of gray cast iron parts with lamellar graphite and perlitic matrix. The heat source used was the electric arc generated between the tungsten electrode (via the TIG process) and the gray cast iron part. The local melting of the surface was performed at different linear energy values (E_l = 3420-5400 J/cm) varying the current between 60 A and 90 A, at a constant voltage of 9.5-10 V. The results showed an increase of the surface hardness from 192 to 198 HV5 to 700-740 HV5 and an improvement of the cavitation erosion resistance, the mean penetration depth of the erosion decreasing by 2.4 times, and the erosion rate by 3.56 times. Optical and scanning electron microscope were used to characterize the microstructure and to identify the phases in the re-melted area. The results showed that the melting of the surface led to an almost complete dissolution of the graphite lamella; the fine microstructure after re-solidification was composed of dendrites of transformed austenite embedded in ledeburite, consisting of transformed austenite and cementite Fe_3C. Austenite dendrites have a preferential orientation and martensite needles are formed inside some of them.
Ronnie G. WoodwardAthanasios ToumpisAlexander Galloway
13页
查看更多>>摘要：The present study investigates the tribological properties of G350 grey cast iron in various microstructural conditions. Quench and temper heat treatments were conducted at four tempering temperatures, from 400℃ to 700℃, to produce a range of tempered martensitic disc samples. Pins were slow furnace-cool annealed to produce a coarse pearlitic microstructure with some areas of ferrite. These samples were then used in pin-on-disc sliding wear tests. Hardness decreased with tempering temperature, from 400HV at 400℃ to 200HV at 700℃. The two spheroidized carbide discs produced higher volume losses than the two acicular martensitic discs due to instability of the oxide layer on the softer substrate. Subsurface deformation was visible in the annealed pins and spheroidized discs which consisted of deformed cementite lamellae in the direction sliding and strained ferrite grains.
查看更多>>摘要：Stellite alloys are widely utilized in aerospace and automotive applications due to their excellent wear resistance which is strongly dependent on the mechanical mixture layer (MML). However, the formation of MML under light load or low temperature is significantly restricted, leading to poor tribological performance. This study reported the tribomechanical evaluations of different CoCrWAlNixAly alloys obtained by direct laser deposition, with specific attention to the impact of aluminum and nickel content on the structure-property relationship. The wear performance was evaluated by a ball-on-disc test and microstructural features of worn surface and subsurface were characterized by SEM, XPS and TEM. Results indicated that both aluminum and nickel facilitate the formation of MML consisting of nano-oxides, whereas the resultant wear resistance varies. The MML formed by the aluminum addition was beneficial for lubrication and wear resistance where the reduction of both mass and volume loss by 50% was determined. In comparison, the MML formed by the nickel addition at a higher temperature was easy to peel off, indicating less efficient protection. Finally, an improved wear model for the cobalt-based alloy was proposed to reveal the characteristics of MML based on the analysis of the theoretical stress field.
查看更多>>摘要：Reaction-bonded SiC/Si (viz. RB-SiC/Si, also known as SiC particle-reinforced Si matrix composite) possesses high brittleness and hardness, which benefit its engineering applications such as mechanical seals and water-lubricated bearings, but limit its micro-machining strategies simultaneously. In this paper, a purely mechanical method, solid particle erosion (or air-driving slurry jet impact, also called multiphase jet machining), was attempted to create micro-textures on this composite. The material removal behaviour was presented in detail and compared with the behaviour of neat Si. First, the related mechanisms were discussed; i.e., Si showed similar erosion appearances when subjected to the action of hard abrasives, while RB-SiC/Si showed completely different apperances. The dependence of erosion on impact angle for Si showed a typically brittle response while that for RB-SiC/Si showed a semi-brittle response when using small particles, but displayed a typically brittle response when using large particles. Particular attention should be paid to the synergistic effect between the material microstructure and employed particle size, which has an inherent correlation to the shift in maximum erosion from 90° to 75°/80°. Achieved erosion information may provide reference for the jet machining of composite materials and the design of functional materials with erosion-resistant structure in the future.
NSTL
Elsevier