查看更多>>摘要：? 2021 Elsevier B.V.This research studied the effect of quenching and tempering combined with shot peening on the wear and friction behavior of medium carbon steel used in fasteners under lubricated sliding conditions. Shot peening and quench-tempering processes both produced higher compressive residual stress on the disks. During tribo-tests, the tangential shear force and frictional heating generated by frictional contact produced significant plastic deformation by a ratchetting process. The pearlite/tempered martensite beneath the worn surface experienced significant plastic deformation along the sliding direction. Shot peening resulted in more wear and overfoldings on the surface of soft quenched-tempered and shot peened disks rather than on the hard quenched-tempered and shot peened disks. The tempered martensitic/pearlite microstructures on the top of worn surfaces displayed mechanical fracture, fragmentation, and cracks.
查看更多>>摘要：? 2021 Elsevier B.V.In this study, the metallographic structure and wear behaviour of boron-coated rail steels were investigated. For this purpose, the wear behaviour of boronized rail steels was examined under two different load and sliding speed conditions. According to the results, the thickness and hardness values of the boride layer increased with increasing boronizing temperature. The hardness of the rail steel, initially ～300 HV, reached the value of 1886, 2145 and 2590 HV at 700-800-900 °C, respectively. When the wear behaviour of the boronized rail steel was analyzed, a considerable increase in wear resistance was achieved compared to the untreated sample. Topographic images showed that boronized samples have a smoother surface form, while untreated samples have deep valleys and intense fluctuations.
查看更多>>摘要：? 2021 Elsevier B.V.The fabrication of microstructures on surfaces is an innovative approach to relieve slurry erosion. Understanding the effect of the dimensions of the surface microstructure on slurry erosion can inspire new surface treatments, not only for small flow-handling parts but also for large water conservancy facilities. Our previous work has studied the effect of the micro structure's shape on slurry erosion. As an extension, the dimension was investigated based on the selected groove structure. Five V-shaped grooved surface microstructures (V1–V5) with different depths (1–5 mm, respectively) were designed. The effect of groove depth on erosion was studied by scanning electron microscopy observation and mass loss, roughness, and residual stress measurements at a slurry speed of 8.29 m s-1, particle size of 75–150 mesh, and sand concentration of 3 wt%. The results showed that the best erosion resistance occurred at a critical depth of 3 mm. This was partially due to the low-velocity component in the flow direction and the upward velocity component perpendicular to the flow direction. This velocity distribution inhibited the impingement erosion of the particles inside the groove and simultaneously slowed the incoming particles into the groove. The groove surfaces underwent the most severe erosion, while the top surfaces experienced less erosion, which was relieved by multiple vortices induced by the grooves. The erosion rates of V3, V4, and V5 were lower than those of V1 and V2. The erosion mechanisms are summarized to guide the design optimization of surface microstructures.
查看更多>>摘要：? 2021 Elsevier B.V.In the future, humanity will be under great ecological pressure to efficiently use resources and reduce energy and resource consumption. Tribology is not a directly visible consequence of human activities and is divided into energy consumption due to friction losses and additional resource consumption through wear and failures of machine elements and products. Based on the material streams allocated to applications with tribosystems or those depending on tribosystems, the contribution of increased longevity to reduce CO2 emissions is refined. Depending from the absolute amount of material stream considered, its portions allocated to tribology and assuming doubling the service life result in average in savings of 1.06–3.70 gigatons in mass of resources per year or of embedded 1.68–6.77 gigatons CO2eq.per year.
查看更多>>摘要：? 2021 Elsevier B.V.Adhesion layers and intermediate layers exert important effects on the adhesion and cutting performance of PVD multilayer coatings. In this work, TiAlSiN multilayer coatings with different combinations of adhesion layers and intermediate layers were deposited, and their microstructure, adhesion and milling performance were assessed. Rockwell indentation and scratch results showed that delamination from the interfaces between the adhesion layers and intermediate layers occurred both for the T1 coating (TiN adhesion layer + Al17.5Ti80Si2.5N intermediate layer) and T2 coating (Al33Ti67N adhesion layer + Al43Ti54Si3N intermediate layer). Synchrotron radiation glancing incidence X-ray diffraction (SR-GIXRD) investigation on T2 coating revealed the discontinuities in lattice constant a and micro-strain at the interfaces between intermediate layer and adhesion layer, which resulted in poor cohesion of them. The T3 coating (Al67Ti33N adhesion layer + Al64Ti34Si2N intermediate layer) exhibited the lower residual stress (?3.7 GPa), and better cohesion and adhesion (Lc2 = 72 N). The T3 coating also had the longer milling life corresponding to a cut length 1700 m, due to its better cohesion and adhesion increased the “steady wear” stage. This improved cohesion and cutting performance of the multilayer coatings could be achieved by using proper combinations of adhesion layers and intermediate layers.
查看更多>>摘要：? 2021 Elsevier B.V.This study focuses on the analysis of the surface material integrity of the polished, rigid, solid surface of an aluminium alloy after periodical impingement of liquid droplets with variable volume and impact frequency distributions normal to the solid surface. The volume of water droplets was determined for the pressures of 20 and 40 MPa. By increasing the traverse speed of the ultrasonic pulsating water jet head with respect to the stationary tested specimen, the number of water droplet impacts on one area was controlled in order to reach the early erosion stages. Also, for the comparative study, aluminum alloy was exposed to continuous water jet for both supply pressure 20 and 40 MPa with traverse speed of 1 mm/s over the material surface. Systematic testing focused on material integrity in the early erosion stages in the interval between the elastically deformed surface and material disintegration was conducted with the aid of microhardness measurements, X-ray analysis of stress state, and microstructural analysis by SEM. The motivation for carrying out this experiment was to verify the effects of periodic drops on the integrity of the material and to identify the parameters leading to surface strengthening without erosion as compared to continuous jet. Such surface treatments can improve fatigue life, similarly to shot peening.
查看更多>>摘要：? 2021 Elsevier B.V.The erosion mechanism of 2Cr13 stainless steel under ultrasonic cavitation was investigated. The cavitation erosion process investigated in this paper included the incubation period and acceleration period. Microhardness measurement and transmission electron microscopy showed that the surface was deformed and hardened, the grains on the eroded surface layer were refined by nanograins and subgrains. Scanning electron microscopy and electron backscatter diffraction analysis showed that cracks were initiated at the grain boundaries and subgrain boundaries, pits were from the carbide-matrix interfaces and defect microholes, in the incubation period, cracks were grown across the grain into peelings, pits were connected into microholes. In the acceleration period, cracks were initiated at and propagated along the grain boundaries and subgrain boundaries. Kernel average misorientation (KAM) was utilized to show the strain at the grain boundaries and subgrain boundaries and to estimate the density of the geometric necessary dislocations (GNDs) along the depth after cavitation erosion. The thickness of the strain layer after cavitation erosion was not more than 23 μm. The surface fatigue failure was caused by the plastic deformation and stress concentration under the continuous cavitation impacts.
查看更多>>摘要：? 2021 Elsevier B.V.Interaction between nickel base superalloy ZhS6U used as a friction processing tool for in-situ synthesis of intermetallics in Ti6Al4V and this titanium alloy metal has been studied. Severe abrasion-adhesion wear was localized on the tool’ pin areas while shoulder was protected by mechanically mixed layer. Generation of titanium enriched mechanically mixed layers (MML) on the tool's surface was observed whose chemical and phase compositions corresponded to those of Ti2Ni and Ni4Ti3 intermetallic compounds. Fine-crystalline transition layer (TL) was found below the MML which contained high amount of tungsten in the form of fine MC carbide network. Dissolution of initial M6C carbides and diffusion of their components to the MML where new MC-type carbide network formed after stopping the FSP. The MML fragments detached from the tool surface and then were intermixed with the titanium alloy stir zone.
查看更多>>摘要：? 2021 Elsevier B.V.Shape Memory Alloys (SMAs) have shown superior mechanical properties including improved wear resistance compared to their conventional counterparts of the same surface hardness. Available wear models cannot estimate a wear coefficient for SMAs, since they do not consider the effects of phase transformation and the related phenomena. This study presents a methodology considering thermomechanical behavior of shape memory alloys in sliding wear. Wear analysis is carried out for a superelastic SMA under different loads and temperatures, and the results are validated by experimental findings. The proposed approach introduces a constant wear coefficient at different loads and temperatures supporting its reliability for quantitative description of wear in an SMA.
查看更多>>摘要：? 2021 Elsevier B.V.The cutting edges of micro-milling tool undergo degradation with time, in the form of continuous abrasion and intermittent chipping. As a result, the cutting tool looses its original profile and consequently affects the quality of molds and dies manufactured using micro-milling process. This work therefore focuses on understanding the physics and mechanism of tool wear in micro-milling as function of tool life, and to model the transient degradation of cutting tool, which was not investigated in-depth in the literature. Extensive micro-milling experiments were done till the end of tool life, to investigate cutting edge degradation. Further, analytical as well as empirical models were developed to predict continuous abrasion interrupted by chipping, and to determine cutting edge profiles as a function of tool life. The abrasion wear model involved modifying Archard's equation and evaluating tool wear coefficient empirically using a novel pin-on-disk device. The interrupted chipping wear phenomenon during micro-milling was identified by locating sudden drop in resultant forces on the tool. The chipping wear was then modeled using the dimensions of the chipped portions, extracted from the tool images captured in-situ. It was observed from the experiments that the length (C) of the chipped portions of the cutting edges was between 15.76 to 96 μm, whereas, their width (H) was between 7 to 29 μm, and they were found to have a positive correlation. The chipping load estimated from the resultant force, and the load inclination angle evaluated from the chipping model were found to have an inverse correlation, and varied between 1.23 to 3.75 N, and 69 to 25° respectively. The proposed abrasion and chipping wear model jointly gave transient progression of total volumetric tool wear area, and consequent cutting edge profiles over the tool-life cycle. The proposed tool wear model predicted the total wear within 9.3% of the experimental values.
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