不同载荷下Ekonol/G/MoS2/PEEK复合材料的摩擦学性能

用模压方法制备了Ekonol／G／MoS2／PEEK复合材料,对其在不同载荷下的摩擦学性能进行了研究,并用SEM对磨损表面进行了观察和分析,在此基础上探讨了复合材料的磨损机理。结果表明：复合材料的摩擦因数与载荷的大小无关;随着载荷的增大,复合材料的磨损量增加,耐磨性降低,且磨损机理由粘着磨损向磨粒磨损发生转变。     

一种基于气压悬浮磨料池光整加工方法的研究

针对复杂曲面难加工零件,提出一种基于气压悬浮磨料池光整加工方法:采用气压悬浮磨料的混合方式,工件表面与流态化磨料产生相对运动速度,从而使固体颗粒与工件表面发生微观二体磨料磨损。通过对磨粒进行动力分析以及气固二相流加工机理分析,揭示了磨料池内部气体和磨料混合及扩散规律。利用光整加工实验确定了光整加工过程中最佳的主轴转速和工件进给速度,当磨料池的管道布局方式为螺旋上升时,光整加工效率最高,表面质量最好。     

一种新型摩擦材料在水润滑下的摩擦学性能研究

采用环块式摩擦磨损实验研究了一种新型摩擦材料在水润滑状态下不同载荷与转速对试样摩擦学性能的影响,并对比干摩擦条件下的摩擦学性能变化,借助磨损表面形貌观察分析其磨损机理。实验结果表明:水润滑条件下,摩擦系数随着载荷的增大而减小,随着转速的提高先增加后减小;磨损率随着载荷与转速的提高都减小。相同载荷与转速下,干摩擦时磨损机理以磨粒磨损和黏着磨损为主,而水润滑条件下水形成边界润滑,磨损机理以磨粒磨损和轻微的黏着磨损为主;水润滑条件下摩擦系数和磨损率均低于干摩擦,主要是由于水起到了润滑和冷却的作用,阻止了转移膜的形成,并在材料表面形成水膜起到了边界润滑的作用。     

Effect of boronising on friction and wear of ferrous metals

Boronising is a surface diffusion treatment analogous to carburising, but produces harder surfaces without recourse to quenching. Friction and wear resistance of boronised coatings have been evaluated on steels and grey cast iron under dry sliding conditions. Boronising inhibits adhesive wear during running-in and at loads above the mild/severe transition load. The onset of severe wear is prevented until the boronised layer has been worn away, its life expectancy is extremely long and is inversely related to applied load.Boronising has considerable advantages over other similar surface conversion treatments under adhesive wear conditions and is likely to find application at elevated temperatures and under non-oxidising conditions.     

Dry three-body abrasive wear behavior of WC reinforced iron matrix surface composites produced by V-EPC infiltration casting process

This paper fabricated tungsten carbide (WC) particles reinforced iron matrix surface composites on gray cast iron substrate using vacuum evaporative pattern casting (V-EPC) infiltration process, investigated dry three-body abrasive wear resistance of the composites containing different volume fractions of WC particles, comparing with a high chromium cast iron. The fabricated composites contained WC particles of 5, 10, 19, 27, 36, and 52 vol.%, respectively. The results in abrasive wear tests showed that, with the increase in the volume fraction of WC particles, the wear resistance of the composites first increased until reached the maximum when the volume fraction of WC was 27%, then decreased, and was 1.5–5.2 times higher than that of the high chromium cast iron. The changes of the wear resistance of the composites with the volume fraction of WC particles and the mode of material removal in dry three-body abrasive wear condition were analyzed.     

Tribological Behaviour of Pure Ti with a Nanocrystalline Surface Layer Under Different Loads

Surface mechanical attrition treatment (SMAT), a novel surface severe plastic deformation method, was carried out for titanium (Ti) to create a gradient-structured Ti (SMAT Ti). The tribological behaviour was studied under different loads and dry sliding conditions. The results showed that the deformation layer of SMAT Ti was about 160 μm. The friction and wear results showed that the wear resistance of SMAT Ti was enhanced compared to the coarse-grained (CG) counterpart. SMAT Ti showed abrasive wear under 1 and 5 N, and exhibited abrasive and adhesive wear under 2 N. While CG Ti showed abrasive and adhesive wear under 1–2 N, and exhibited abrasive wear under 5 N for the work hardening effects.     

Tribological properties of carbon nanotube-doped carbon/carbon composites

Carbon nanotube (CNT)-doped carbon/carbon (C/C) composites were fabricated by the chemical vapor infiltration (CVI) method to investigate the effect of CNTs on tribological properties of C/C composites. CNTs, which had been synthesized by catalytic pyrolysis of hydrocarbons, were added to carbon fiber formed preforms before CVI process. Ring-on-block-type wear tests were performed to evaluate the frictional properties of CNT-doped C/C composites. Results show that CNTs can not only increase wear resistance of C/C composites but also maintain stable friction coefficients under different loads. Polarized light microscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy analyses demonstrate that favorable effects of CNTs on tribological properties of C/C composites have been achieved indirectly by altering microstructure of pyrocarbons and directly by serving as high-strength lubricative frictional media at the same time. Electron dispersive spectroscopy (EDS) analyses verify the existence of adhesive wear mechanism in both pure C/C composites and CNT-doped C/C composites albeit the two-body abrasive mechanism dominates in pure C/C composites.     

Wear reducing effects and temperature dependence of tribolayer formation in harsh environment

Certain materials show a tribolayer formation especially at enhanced temperatures in abrasive environment, building a wear protection layer with the abrasive on the surface. Three materials with different microstructures were tested in three-body abrasive and impact/abrasive environments at temperatures up to 700 °C to investigate tribolayer formation. Optical and electron microscopical methods were used for wear qualification. Furthermore, hot hardness tests were performed up to 700 °C to investigate the influence of hardness drop on tribolayer formation.It was shown that no significant tribolayer formation occurs on grey cast iron, whereas other materials form tribolayers. Generally, tribolayer formation increases with increasing testing temperature, especially for austenitic and ferritic materials. This entails a self-protecting effect and thus superior wear resistance in abrasive environment.     

碳纤维增强尼龙1010复合材料的摩擦磨损性能及磨损机理研究

以注塑成型法制备了尼龙1010及碳纤维(CF)增强尼龙1010复合材料，研究了CF含量和载荷对材料摩擦学性能和磨损机制的影响。结果表明，CF的加入可显著改善尼龙的摩擦学性能，以体积分数为20％的CF增强尼龙1010复合材料的耐磨性能最好。较低的CF含量下复合材料磨损表面主要受到对偶钢环上微凸峰的切削和犁沟作用，较高载荷时发生了热疲劳剥层磨损；随着CF含量增加，复合材料表面在较高载荷时产生明显疲劳断裂，并使对偶钢环产生较剧烈磨损。     

硬质颗粒复合合金的组织和耐磨性

本文强调基体合金组织对硬质颗粒复合合金耐磨性的决定作用,设计并通过“真空吸附铸件表面合金化工艺”,在灰铁铸件表层稳定地制得了以不同粒度的铸造碳化钨颗粒均匀分布于高合金铬钨白口铸铁中的复合合金。磨料磨损试验表明：基体合金组织对复合合金二体尤其是三体高应力磨损耐磨性有决定性的作用;以马氏体合金白口铁为基体合金的复合合金,在二体及三体磨损条件下均具有极高的耐磨性,铸造碳化钨颗粒愈粗,复合合金耐磨性愈高,当颗粒尺寸由140～200目增大到18～28目时,其在二体和三体磨损条件下的耐磨性分别是马氏体白口铁15Cr2Mo1Cu的9～31倍和2.8～6.7倍。     

Repeated impact-abrasion of ore-crushing hammers

The wear processes which occur on swing hammers used to comminute an abrasive ore were investigated. The performance of martensitic cast steel and white cast iron hammers was studied to assist in the development of valid simulative wear tests by documentation of the mechanisms by which wear takes place in a repeated impact-abrasion application. The principal mechanism of material loss of the martensitic steel was microspalling, produced by subsurface fracture through a hard brittle white-etching layer developed at the wear surface. Wear of the white cast iron was controlled by the preferential fracture and subsequent spalling of eutectic carbides at the surface, thereby causing the brunt of the ore impacts to be borne by the secondary-carbide-enriched matrix. An explanation of the eutectic carbide fracture process is made based on the interaction of stress waves with the constituents of the microstructure.     

Wear mechanisms in ball-cratering tests with large abrasive particles

Three-body abrasive wear resistance of mild steel and 27%Cr white cast iron was investigated using a ball-cratering test. Glass beads, silica sand, quartz and alumina abrasive particles with sizes larger than 200 μm were used to make slurries. It was found that the wear rates of mild steel increased with sliding time for all abrasive particles tested, while the wear rates of 27%Cr white cast iron were almost constant with sliding time. This increase in the wear rates of mild steel was mainly due to the gradual increase in ball surface roughness with testing time. Abrasive particles with higher angularity caused higher ball surface roughness. Soft mild steel was more affected by this ball surface roughness changes than the hard white cast iron. Generally, three-body rolling wear dominated. The contribution of two-body grooving wear increased when the ball roughness was significant. The morphological features of the wear scars depended on the shape of the abrasive particles and also on the hardness and microstructure of the wear material. Angular particles generated rough surfaces similar to those usually observed in high angle erosion tests. Rounded particles generated smoother surfaces with the middle area of the wear craters having similar morphology to those observed in low angle erosion.     

Abrasive wear behaviour of laser sintered iron–SiC composites

Direct metal laser sintering (DMLS) is one of the popular rapid prototyping technologies for producing metal prototypes and tooling of complex geometry in a short time. However, processing of metal matrix composites (MMCs) by laser sintering is still in infant stage. Thermal cracks and de-bonding of reinforcements are reported while processing MMCs by laser sintering process. There are reports on use of metallic-coated ceramic reinforcements to overcome these problems. The present investigation is aimed at using nickel-coated SiC in developing iron composites by DMLS technique and to characterize its abrasive wear behaviour.Microstructure, microhardness, and abrasive wear tests have been carried out on both DMLS iron and its composites sintered at a laser scan speed of 100 mm/s. Abrasion wear tests have been carried out using a pin-on-disc type machine. SiC abrasive papers of grit size 60, 80, and 150 having an average particle size of 268, 192, and 93 μm, respectively, have been used. Load was varied between 5 and 25 N in steps of 5, while the sliding distance and sliding velocity of 540 m and 2.5 m/s, respectively was adopted for all the tests. Optical, scanning electron micrograph and surface roughness observation of worn surfaces have been undertaken.An increase in microhardness and a decrease in density of the laser sintered iron–SiC composites was observed with increase in SiC content. The abrasive wear resistance of composites increases with increased content of SiC in iron matrix. For a given grit size of SiC abrasive paper, at all the loads studied, iron–SiC composites exhibit excellent abrasive wear resistance. Increase in abrasive wear was observed with the increase in abrasive particle size.     

Microstructure and Tribological Properties of a HfB<Subscript>2</Subscript>-Containing Ni-Based Composite Coating Produced on a Pure Ti Substrate by Laser Cladding

A HfB₂-containing Ni-based composite coating was fabricated on Ti substrates by laser cladding, and its microstructure and tribological properties were evaluated during sliding against an AISI-52100 steel ball at different normal loads and sliding speeds. The morphologies of the worn surfaces were analyzed by scanning electron microscopy (SEM) and three-dimensional non-contact surface mapping. The results show that wear resistance of the pure Ti substrate and NiCrBSi coating greatly increased after laser cladding of the HfB₂-containing composite coating due to the formation of hard phases in the composite coating. The pure Ti substrate sliding against the AISI-52100 counterpart ball at room temperature displayed predominantly adhesive wear, abrasive wear, and severe plastic deformation, while the HfB₂-containing composite coating showed only mild abrasive wear and adhesive wear under the same conditions.     

A comparative investigation of the wear behavior of PTFE and PI under dry sliding and simulated sand-dust conditions

The wear behavior of polytetrafluoroethylene (PTFE) and polyimide (PI) has been comparatively evaluated under dry sliding and simulated sand-dust conditions. An improved block-on-ring wear tester equipped with an attachment for simulating the sand-dust environment was used to evaluate the abrasive wear behavior of materials. The sand collected from the Yellow River of China was used to simulate the sand-dust environment, also different loads and sand-dust sizes were chosen for tribological tests. The two chosen polymers showed different wear behavior under sand-dust conditions and the wear rates of PTFE were much lower under sand-dust conditions than under dry sliding conditions. This was attributed to the formation of the tribolayer on the worn surfaces during the abrasive wear process. The sand-dust enhanced the wear resistance of PTFE, but reduced that of PI because, in contrast to PTFE, there was no tribolayer formed on the PI worn surface. The wear rate of PTFE increased under sand-dust conditions while the wear rate of PI decreased with the increase of applied load. The higher hardness of PI and fragmentation of abrasive particles under high loads accounted for the decrease in wear rate as load increased.     

Optimisation of electron-beam surface hardening of cast iron for high wear resistance using the Taguchi method

The paper presents the application of the Taguchi method to develop an optimised electron-beam surface hardening of cast iron for high wear resistance. The experiments were conducted on both the ductile and grey cast iron. The factors investigated during the surface-hardened process included the material matrix, the accelerating voltage, the electrical current, the travel velocity, the melted width, the beam oscillation, and the post-heat treatment temperature. In this study, the L18 and L9 orthogonal arrays were introduced through the two-stage experimental designs and trials. Smaller-is-better was used as a quality characteristic to evaluate the experimental results by computing their signal-to-noise (S/N) ratios of the wear volume after wear tests.It was found that using the Taguchi method coupled with a two-round experimental design strategy is simple, effective and efficient in developing an optimised EB surface hardening process. The experimental results show that the most important process parameters identified are the accelerating voltage, the travel speed, the electrical current and post-heat treatment, respectively. The best wear resistance result obtained through the best combination of process parameters is 8.845×10⁸ kg-mm/mm³.     

浸酚醛树脂石墨/SiC密封材料摩擦学特性研究

采用UMT-3多功能摩擦磨损试验机研究了3种国产典型浸酚醛树脂石墨与SiC陶瓷配对副在干摩擦和油润滑条件下的摩擦学特性,结果表明：干摩擦下,摩擦因数随载荷p与速度v的乘积（pv值）的增大呈下降趋势;pv值较小时,磨损机理主要为轻微黏着磨损和磨粒磨损,pv值较大时则变为严重黏着磨损、磨粒磨损和疲劳磨损;相同条件下的磨损率受速度的影响比受载荷的影响更大;油润滑下,摩擦因数保持在0.1左右,磨损机理主要为黏着磨损和疲劳磨损;pv值增至5 MPa·m/s时,干摩擦下3种浸渍石墨摩擦副表面最大温升为21.1 ℃,油润滑下最大温升为14.9 ℃且H1石墨温升均最低。综合考虑浸渍树脂石墨的力学性能、摩擦学特性和端面温升,推荐石墨化度为45%～55%。     

Surface topography and tribology of cast iron in boundary lubrication

This work aims to study and understand the influence of the surface topography on wear of grey cast iron used for heavy duty diesel engine cylinder liners. A micro-alloyed grey cast iron was tested with different surface topographies. These were polished surfaces, honed surfaces (with two different honing parameters) and three model surfaces with well defined grooves on a polished specimen.Reciprocating friction tests using a steel ball rubbing against a flat or a cylindrical sample (extracted from a cylinder liner) were carried out on a Cameron Plint test rig. A commercial synthetic oil for diesel engine was used as the lubricant. The friction coefficient and the electrical contact resistance were measured during the tests. The wear volume of the cylinder liner part was also measured at the end of the test.The influence of the surface topography on the tribochemical film formation and on the wear behaviour of cast iron was established. Surfaces exhibiting lots of surface asperities had the highest wear, mainly due to delayed formation of protective tribochemical film. In our test conditions, the spacing between the grooves on model specimens had no influence on the wear behaviour of the cast iron specimens.     

Particle size effect on abrasion resistance of mottled cast iron with different retained austenite contents

Effects of particle abrasive sizes on wear resistance of mottled cast iron with different retained austenite contents were studied. Abrasive wear tests using a pin test on alumina paper were carried out, using abrasive sizes between 16 μm and 192 μm. Retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of samples and the alumina paper were examined by scanning electron microscopy for identifying the wear micromechanism. The results show that at lower abrasive sizes the mass loss was similar for the iron with different austenite contents. However, at higher abrasive sizes the samples with higher retained austenite content presented higher abrasion resistance. For lower abrasive sizes tested, samples with higher and lower retained austenite content both presented microcutting. On the other hand, the main wear micromechanism for the samples with higher retained austenite content and higher abrasive sizes was microploughing. The samples with lower retained austenite content presented microcutting and wedge formation at higher abrasive sizes. Higher abrasive size induced more microcutting in samples with lower retained austenite. The iron with lower retained austenite content presented wider grooves for the different abrasive sizes measured. SEM on the abrasive paper used on samples with higher retained austenite showed continuous and discontinuous microchips and the samples with lower retained austenite showed discontinuous microchips at 66 and 141 μm. This research demonstrates the relation between abrasive size, wear resistance, groove width and wear micromechanism for mottled cast iron with different retained austenite contents.     

铸铁CrMo表面激光熔覆Ni基高温合金粉末的磨损特性

采用激光熔覆技术在铸铁CrMo表面制备了Ni基高温合金熔覆层,采用SEM和晶相仪分析了激光熔覆层的晶相组织。采用回归正交试验方法,研究了基体和熔覆层在不同载荷和速度下的磨损特性。结果表明,熔覆层与基体形成良好的冶金结合,熔覆层组织致密,主要由树枝晶和共晶构成,熔覆层和基体材料的磨损机制为磨粒磨损;铸铁CrMo表面激光熔覆Ni基高温合金粉末可以提高表面的耐磨性能。