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Investigation of techniques for determining the residual stresses in WC-17Co thermal sprayed coatings and studying the effect of residual stress on its abrasion resistance

机译：研究确定WC-17Co热喷涂涂层中残余应力的技术以及研究残余应力对其耐磨性的影响

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摘要

The aim of this project was to investigate the techniques for determining the residual stressesudin WC-17Co thermal sprayed coatings and to study the effect of residual stress on abrasionudresistance on different substrates. The choice of the substrate was due to their differentudcoefficients of thermal expansion (aluminium, super-invar, 304L stainless steel, mild steeludand brass). Coatings of about 200μm were successfully deposited on all the substrates.udCoatings were deposited by a high velocity oxyl-fuel spraying system (HVOF), andudcharacterized by evaluating the coating phases and wear resistance, and the residual stressesudwere determined via non-destructive methods. Investigations involved both as-sprayed andudtheir annealed counterparts to ascertain the effect of heat treatment.udNon-destructive determination of residual stresses in the WC-Co coated systems wasudexceptionally challenging in that the coatings were only 200 microns thick. The best suitedudtechniques for investigation of WC were diffraction-based strain scanning using penetratingudradiation such as thermal neutrons (most penetrating), high energy synchrotron X-rays (100udkeV enables 20 micron penetration) and laboratory X-rays (limited to 5 micron penetration).udLaboratory X-rays (Necsa, using Co radiation), thermal neutrons (ANSTO, Australia) and Xrayudsynchrotron (ESRF, France) were successfully employed to resolve the stress conditions.udThe neutron investigations enabled two approaches for the determination of the in-surfaceudstresses, direct measurements (good results for the low neutron attenuation substrates), andudindirect determination using stress balance conditions inferred from the through thicknessuddepth profiles measured in the substrates (applicable to all the higher neutron attenuatingudsubstrates). Investigations were expanded to the study of the influence of annealing at 40% ofudthe respective substrate melting temperatures. For each substrate, the through thickness stressudprofile differences between the grit-blasted reference material (final before the HVOFudcoating) and the grit-blast coated samples were used to determine the elastic contributionsudpurely ascribed to the coating process. This required exceptional positional resolution neutronuddiffraction investigations (positional accuracies better than 0.01 mm). There were both smalludcompressive and low tensile stresses on the as-sprayed coated samples. After annealing, theudstresses became substantially more compressive. The near-surface trends of the grit-blastedudsubstrates were completely relaxed after annealing, with thermal stresses being the dominantudmechanism for residual stress induced due to the large difference in the coefficients ofudthermal expansion (CTE) between the WC coatings and the substrates.udThe three-body abrasive tests were carried out on the parent materials (substrate), grit blastedudsubstrates, as-sprayed coatings and heat treated coatings. The contributions of each coatingudprocess were established. There was about 45-50% reduction in the wear of grit-blastedudsamples compared to the substrates, whilst 80-95% reduction in the wear of the coatingsudcompared to substrates was found. The wear resistance is due to many different contributions,udbut there was a strong correlation between the residual stress and wear resistance of the coating.
机译：该项目的目的是研究确定残余应力 udin WC-17Co热喷涂涂层的技术，并研究残余应力对不同基材上的耐磨性抗性的影响。基底的选择是由于它们的热膨胀系数不同/铝（铝，超殷钢，304L不锈钢，低碳钢乌德和黄铜）。在所有基底上成功沉积了约200μm的涂层。 ud通过高速氧-燃料喷涂系统（HVOF）沉积涂层，并通过评估涂层相和耐磨性来表征，残余应力通过 n破坏性的方法。为了确定热处理的效果，喷涂和退火都进行了调查。无损确定WC-Co涂层系统中的残余应力是非破坏性的，因为涂层只有200微米厚。最适合研究WC的技术是使用穿透辐照进行的基于衍射的应变扫描，例如热中子（穿透最多），高能同步加速器X射线（100 udkeV能够穿透20微米）和实验室X射线（有限 ud实验室X射线（Necsa，使用Co辐射），热中子（澳大利亚ANSTO）和Xray udsynchrotron（法国ESRF）已成功用于解决应力条件。 ud中子研究使两个用于确定表面内 udstress的方法，直接测量（对于低中子衰减基板而言是良好的结果）和 u使用从基板中测得的贯穿厚度 uddepth轮廓推断出的应力平衡条件进行的间接确定（适用于所有高中子衰减底物）。研究扩展到研究在各自衬底熔化温度的40％处退火的影响。对于每个基材，使用喷砂处理的参考材料（在HVOF udcoat之前进行最终处理）和喷砂处理的样品之间的贯穿厚度应力 udprofile差异来确定弹性归因于涂覆过程。这就需要进行特殊的位置分辨率中子超衍射研究（位置精度优于0.01毫米）。喷涂后的涂层样品既有小无压缩应力又有低拉伸应力。退火后，应力逐渐变得更大。喷砂处理后的 ud基体的近表面趋势在退火后被完全缓和，由于WC涂层和WC涂层之间 udthermal膨胀系数（CTE）的巨大差异，热应力是引起残余应力的主要 udme机制。 ud对母体材料（基材），喷砂 ud基材，喷涂涂层和热处理涂层进行了三体磨料测试。确定了每个涂层 udprocess的贡献。与基底相比，喷砂 udsample的磨损降低了约45-50％，而与基底相比，涂层的磨损降低了80-95％。耐磨性归因于许多不同的原因，但残余应力与涂层的耐磨性之间存在很强的相关性。

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    Oladijo Oluseyi Philip;

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  • 年度 2013
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