查看更多>>摘要：Composite peening is a process to embed ceramic particles into the surface of materials with the aim to improve the mechanical and tribological properties. These properties depend essentially on the penetration depth of the particles. In order to investigate the penetration depth achieved with composite peening, micrographs were taken and evaluated employing digital image processing. In composite peening, the blasting particles penetrate the surface of the substrate depending on the process parameters. Models from the field of solid particle erosion were applied to predict the penetration depth of the particles. These analytical models can be used to evaluate the influence of specific process parameters on the penetration depth in composite peening. Furthermore, an additional model from ballistics was implemented. A good qualitative agreement was found between the analytical approaches and the experiments regarding the penetration depth after composite peening for the given system. In the future, this will allow estimating the penetration depth for other process parameters and materials for composite peening as well as for issues related to solid particle erosion.
查看更多>>摘要：Understanding the structure-property relationship is important for guiding the design of metallic glasses with advanced properties. In this work, we employ nanoscratching experiments to establish a correlation between structure and nano-tribological behavior in Zr-based metallic glasses where the structural state of the material is characterized by its fictive temperature, T_f. The results indicate that independent of the applied load, the scratching depth and residual depth of the scratch track increase with an increase in T_f, which is ascribed to the increase in free volume that metallic glasses experience when they are prepared with higher T_f. Furthermore, it was found that the effect of T_f on the friction coefficient varied significantly with the applied load: At low loads, adhesion-induced friction dominates so that low-T_f samples display higher friction coefficients, which we correlate to their denser packed structure affecting interfacial shear. At high loads, however, plowing becomes dominant, which causes the friction coefficient of low-T_f samples to become lower than the ones of high-T_f samples and is ultimately a consequence the higher elastic recovery capability for the samples with lower T_f. Meanwhile, sudden sink-in events of scratching depth are observed when ramping the load during nanoscratching in the indenter face forward direction, revealing the occurrence of scratch-induced yielding. Thereby, the higher degree to which free volume is available in high-T_f samples causes them to show higher plasticity, which in turn is responsible for the higher critical loads at which the sink-in event occurs. This finding implies the possibility of using ramping load scratching to characterize the ductile-to-brittle transition of metallic glasses as an alternative to carrying out time-consuming fracture tests.
Steven A. PolicastroJ. Michael ShockleyMatthew J. StromChristopher R. So...
12页
查看更多>>摘要：The wear-assisted corrosion response of a super-duplex stainless-steel from a single asperity contact was obtained using atomic force microscopy (AFM). The AFM tip applied increasing loads to an isolated surface region that was polarized to two different static potentials in the passive potential region of the alloy in a 0.6 M NaCl solution. The wear-assisted corrosion response was modeled using an interfacial film growth model to obtain consistent kinetics parameters for the austenite phase response across applied loads and polarization potentials. The average response was then fit with an Arrhenius model that suggested that the stress fields from the single asperity contact induced damage in the protective oxide but also disrupted other oxide-formation processes at the oxide-electrolyte interface, thereby slowing repassivation, and allowing increasingly high corrosion currents as the stress fields increased.
查看更多>>摘要：Cutting tools containing superhard phases enable efficient dry machining resulting in reduced human and environmental risks. In the current work, spark plasma sintered composites containing up to 20 vol% cBN in Al_2O_3-based matrix with an addition of 15 vol% ZrO_2 or 10 vol% TiN have been tested under dry sliding (with multiple restarting to better simulate real working conditions) and surface fatigue (with in-situ monitoring of acceleration indicating evolution of the test area) conditions. Dry sliding was carried under two configurations of "ball above sample" and "ball below sample" to study the effect of wear debris entrapment in a wear scar. The importance of a longer test duration (40 000 s, i.e. more than 10 h) during sliding of extensively polished ceramic materials with "mild" wear regime is emphasized. The reason for long running-in process with characteristic threshold is explained. The worn surfaces were studied using scanning electron microscopy, energy dispersive spectroscopy and 3D profilometry to understand the responsible wear mechanisms. The wear rates are reported in comparison to pure Al_2O_3 ceramic. The surface fatigue test was able to identify the material (Al_2O_3-20cBN-15ZrO_2) that according to previous research by authors exhibits lowest wear in dry cutting conditions.
查看更多>>摘要：In this work, a simulation methodology with the combination of finite element modeling, Archard theory, and Arbitrary Lagrangian-Eulerian (ALE) technique is proposed for the accumulated wear degradation prediction of railway friction block. The validation is conducted with a test bench from the perspectives of tribological and dynamic behaviors during the running-in and formal testing processes. The friction pair comprises a forged steel brake disc and a Cu-based powder metallurgy friction block. The results indicate that the contact area increases during the running-in process and the average contact pressure decreases first and then fluctuates around a stable value. In the formal testing process, although the accumulated wear mass and the wear mass per cycle increase with the number of braking cycles, the increase rate of friction block wear mass decreases rapidly in the first few cycles and then decreases slowly. The prediction error of the proposed method for the accumulated wear mass is less than 5%. The research in this work is helpful to have a deep understanding of the wear degradation mechanism of friction block and can provide an effective method for the prediction of friction block wear degradation.
查看更多>>摘要：In this study, the combined treatment technology of shot peening (SP) and ultrasonic surface rolling (USR) were applied to the surface modification of AISI 52100 steel. The results revealed that SP, USR and combined treatment effectively improved the microhardness and residual stress of the alloy; however, SP and combined treatment were often accompanied by increased surface roughness. A nanocrystalline structure layer was prepared on the surface of the material through combined treatment, and the reason for the formation of the nanocrystalline structure layer was explained in detail. Compared with ceramic beads, the combined treatment of SP with steel beads was beneficial. The surface hardness and residual stress were improved while the minimum surface roughness was obtained. Under this process, the RCF life was significantly increased. Studies have shown that with the increased of RCF life, crack initiation transferred from the surface to the subsurface, and the crack depth increased significantly.
R. S. MirandaA. B. RezendeS. T. FonsecaF. M. Fernandes...
15页
查看更多>>摘要：Railway transport companies in Brazil and worldwide have become more productive and efficient by increasing the weight transported and using faster locomotives. These actions have caused the premature exchange of wheels and rails due to excessive wear and rapid growth of rolling contact fatigue (RCF) cracks, and both consequences have been minimized by the improvement of pearlitic steels of wheels and rails. However, these pearlitic materials have already shown that there is a limit to the optimization of their mechanical properties. The bainitic microstructure could replace the pearlitic one, however few studies on the bainitic microstructure variants have been carried out, which still makes its behavior in rolling and sliding wear - especially in high carbon microalloyed steels - a matter of debate. Those studies are far from reaching a consensus, and, therefore, an important question arises regarding the materials used in the wheel-rail contact: which microstructure has better tribological and fatigue properties being produced from the same steel, having the same hardness, and being influenced by the same tribological variables: bainite or pearlite? In order to answer this question, twindisc tests were performed on forged railway wheel microalloyed steel (7NbMo) with pearlitic and bainitic microstructures with the same bulk hardness and on high carbon steel (7C) with tempered martensite. The results revealed that the microstructure had a significant role in wear and RCF performance. The bainitic microalloyed steel (7NbMo-B) showed lower wear rates and greater resistance to RCF than the pearlitic one (7NbMo-P). Similar behavior was observed for their counter-bodies, indicating that the use of bainite in rolling and sliding wear applications would cause the joint benefit of the body and counter-body.
查看更多>>摘要：Si_3N_4 ceramics with 0 vol% and 5 vol% tungsten particles were fabricated by gas pressure sintering. Commercial Si_3N_4 ceramic balls were used as the tribo-pair to test the influence of the tungsten particles on the wear resistance of Si_3N_4 ceramics. The tungsten particles in the samples were exfoliated and oxidized during the rubbing process. The tungsten oxide was uniformly doped into the wear debris, which turned the harmful exfoliated abrasives into a useful tribo-film. Compared with the monolithic Si_3N_4 ceramic, the abrasive wear of Si_3N_4 ceramics with introducing tungsten particles was almost eliminated, and the oxidative wear and surface fatigue were also reduced. The specific wear rate was reduced by more than an order of magnitude, from 4.70 × 10~(-6) mm~3 N~(-1)·m~(-1) to 3.78 × 10~(-7) mm~3 N~(-1)·m~(-1).
查看更多>>摘要：The wear of parts tribounits under conditions of multicomponent dynamic loading is considered. The results of a comprehensive evaluation of the state of the sample surface after friction using continuous indentation and scanning of the indenter are presented. The analysis of changes in the methods of electron escape from the sample surface is presented. The dependence of the surface layer wear resistance and homogeneity, as well as the microgeometry and the energy contour of the surface on loading conditions is discussed. The authors suggest the concept of wear resistance tribosystems on the basis of the principles structural-energy adaptation of materials in friction under various kinds of loading. The possibility of controlling the wear resistance of the contacting parts when changing the contact time, taking into account the peculiarities of the formation of the surface layer upon contact is shown. The algorithm for controlling the wear resistance surface of steel components the tribounits is developed.
查看更多>>摘要：Ultra-low-wear PTFE nanocomposites rely heavily on water-dependent tribochemistry, which reinforces surfaces by anchoring tribochemically-modified chains to nanofillers and the countersurface. In a recent study, we showed that trace nanofillers (0.1 wt%) reduced the wear rates of an already low wear PEEK-PTFE blend by 40- fold with minimal tribochemistry. Interestingly, wear rates increased by 2-fold at 5 wt% nanofillers despite increased tribochemical accumulation. This observation raises questions about the tribochemical and mechanical roles of nanofillers in this material system, particularly at the surface. This paper aimed to isolate these effects. Specifically, we varied environmental humidity to promote or inhibit favorable tribochemical accumulation while maintaining subsurface stability via PEEK reinforcement. When we discouraged tribochemical reinforcement using a dry environment, high loadings of nanofillers had severely detrimental effects on wear rates and tribofilm stability. For example, the addition of 5 wt% nano-alumina to 5 wt% PEEK-PTFE increased wear rates by > 100-fold in the dry environment. By contrast, the addition of trace amounts (0.1 wt%) of nano-alumina had no detrimental effect on wear rate (10~(-7) mm~3/Nm) or tribofilm stability. These results suggest that the mechanical effects of nanofillers were primarily destabilizing rather than stabilizing and that these effects increased with filler loading. In humid environments, however, these adverse effects of nanofillers, particularly at loadings >1 wt%, were offset by the favorable competing effect of tribochemical accumulation. Trace nanofiller loadings (～0.1 wt%) optimized surface reinforcement at both environmental extremes because they provided the tribochemical benefits of the nanofillers while minimizing their mechanical costs.
NSTL
Elsevier