基于声发射技术的接触疲劳失效检测应用与研究

接触疲劳是齿轮、轴承等长期承受交变载荷的重要旋转零部件的主要失效形式。采用声发射技术对接触疲劳失效过程进行监测,对损伤程度进行检测以及揭示接触疲劳失效机理具有重要的意义。随着声发射技术不断发展及先进声发射信号处理技术的出现,其在接触疲劳失效检测中的研究也越来越深入。文章回顾了声发射技术的发展现状,综述了声发射技术应用于块体零件和涂层零件的接触疲劳失效检测的研究进展与存在的问题,探讨了进一步研究的方向和解决问题的思路。     

Comparative Investigation on Tribological Properties of Ion-Sulfuration Layers Under Dry Friction

Four kinds of steel, including high-speed steel (M2), die steel (L6), stainless steel (420) and plain carbon steel (1045), were treated by low-temperature ion sulfuration. Sulfide layers, dominated by the FeS phase, were produced on the surfaces of the four steels. The tribological properties of sulfide layers were investigated on a block-on-ring test rig under dry friction conditions. The results showed that the tribological properties of all sulfurized steels were remarkably improved. The tribological properties decreased in the order of high-speed steel—die steel—1045 steel—stainless steel. The hardness, microstructure and corrosion resistance of the substrate determined the differences in the tribological properties of different steels.     

基于粒子飞行特性及铺展行为的WC-10Co4Cr涂层孔隙形成机理研究

采用超音速等离子喷涂设备制备WC-10Co4Cr涂层, 通过调整喷涂功率得到了具有不同孔隙结构特征的涂层, 以液氮为冷却介质收集不同熔化状态下的飞行粒子, 并通过镜面钢收集熔滴撞击铺展之后所形成的扁平粒子, 采用扫描电子显微镜观察涂层、收集的飞行粒子及扁平粒子形貌, 采用透射电镜观察涂层显微组织结构。结果表明: 随着喷涂功率的增大, 涂层的大孔隙含量逐渐降低, 而当喷涂功率上升到60 kW时, 涂层内部出现较多的热裂纹, 涂层的显微硬度则随着功率的增加而先增大后减小, WC扁平粒子主要有四种类型, 包括熔化不佳、破碎型、气泡型及花瓣型, 孔隙的形成主要是由于“遮蔽效应”、微区气体作用、熔滴不充分润湿及气孔迁移等。     

基于电阻法的金属材料损伤表征研究现状

电阻率对金属材料微观组织变化具有精确性和敏感性。近年来,随着微电阻测量精度的不断提高,基于电阻法的金属材料损伤表征研究开始大量出现。综述了不同金属材料试样在拉伸韧性损伤、高温时效损伤、高周疲劳损伤和蠕变损伤过程中弹性模量、拉伸强度、断裂韧性、硬度、时效时间和疲劳周次等参量与电阻参量的映射关系,探讨了损伤导致电阻变化的微观机理,指出了今后微电阻法的主要研究方向。     

Chemical and electrocatalytical interaction: influence of non-electroactive ceramic nanoparticles on nickel electrodeposition and composite coating

This article focuses on the nanoparticle electrocatalytical action on electrodeposition of nickel and the chemical combination state between nanoparticles and matrix metal in composite coating. The electrochemical behavior, from common and composite brush electroplating solution, is investigated by cyclic voltammetry. The interaction between nanoparticles and matrix metal nickel is researched by X-Ray Photoelectron Spectrometry (XPS). The microstructure and morphology of coating are observed with Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). The results show that nanoparticles not only can obviously induce the increasing of the current efficiency and decreasing of overpotential, but also can distinctly refine the metal crystal grains of composite coating. The experimental results demonstrate that nanoparticles take part in the electrode reaction and can evidently catalyze nickel electrodeposition. Part of the unsaturated oxygen atoms on nanoparticles surface can combine with some of the absorbed nickel atoms and form nickel-oxygen chemical bonds. There is chemical binding interaction at the interface between nanoparticles’ surface and matrix metal nickel.     

Microstructure and nanoindentation measurement of residual stress in Fe-based coating by laser cladding

Laser cladding is a surface modification technique for improving surface properties. However, high residual tensile stress is always originated, which can create cracks in cladding coatings. The through-thickness residual stresses in Fe-based coating prepared by laser cladding were measured using a non-destructive nanoindentation technique. The cladding coating with a thickness of 1 mm exhibited a uniform appearance, and no crack or defect was observed. An excellent metallurgic bond was obtained between the coating and the substrate. The XRD pattern implied that the coating was mainly composed of α(Fe, Cr) solid solution, Cr₇C₃ hard phase and Fe₂B stable phase. The residual tensile stress in the cladding coating was found to increase as the increasing of the distance from coating surface. Although the tensile residual stress reaches the highest magnitude of 700 MPa up to the depth of 600 μm, no dehiscence happened. The prepared cladding coating has good plasticity and toughness, as well as low crack sensitivity.     

A separation of experimental study on coatings failure signal responses under rolling contact

The objective of present study is to address the signal responses of the acoustic emission (AE), vibration and torque in rolling contact fatigue (RCF) tests of the coatings. The Fe-Cr alloy coatings were deposited using plasma spraying technique. The AE, vibration and torque sensors were assembled to detect the coating failures during the RCF tests, respectively. The results show the signal responses of the vibration and torque accurately indicate the RCF failures of the coatings, but based on the coating losses. The AE signals can sensitively monitor fatigue fractures prior to the formation of the final failure.