超音速火焰喷涂WC-10Co4Cr涂层及其耐微动磨损性能

HVOF Sprayed WC-10Co4Cr Coating and Its Fretting Wear Resistant Properties

摘要:

航空、舰船用发动机零部件的喷涂耐磨涂层需具有抗摩擦磨损性能，其中碳化钨（WC-Co）涂层是500 ℃以下最常使用的耐磨涂层之一。然而，目前使用的WC-12Co等常规碳化钨耐磨涂层在高温、高湿、高盐等海洋环境下耐腐蚀性能较差，使用寿命较短，使长期在海洋腐蚀环境下服役的舰船用发动机的压气机机匣等涂层零件存在过早失效的风险。超音速火焰（HVOF）喷涂，可使喷涂粉末颗粒的速率达600—1 000 m?s^-1，对零件喷涂表面的冲击动能大，制备出的涂层孔隙率小、组织致密、硬度高、拉伸结合强度大且加工后表面光滑，具有显著的耐磨损性能。HVOF喷涂制备的WC-10Co4Cr涂层，由于粉末中细小碳化钨（WC）颗粒和Co金属合金粘结剂中固溶的金属铬（Cr）可增强涂层的抗腐蚀性能，从而延长磨损零件在海洋环境中的使用寿命。因此，以煤油和氧气为喷涂燃料，采用超音速火焰喷涂喷雾干燥烧结WC-10Co4Cr粉末的方法，在GH907变形高温合金基体试样表面制备WC-10Co4Cr耐磨耐腐蚀涂层。结果表明，WC-10Co4Cr涂层为高密度涂层，孔隙率为0.63%，表面颗粒细小且粗糙度（Ra）值在2.5 μm以下。这是由于在喷涂过程中，喷雾烧结粉末中强化相WC颗粒棱角部位固溶在熔融Co合金中，且均匀、弥散分布在涂层内。XRD分析结果表明，WC-10Co4Cr涂层主要由WC和Co非晶合金两相组成，另外还有少量的W₂C相。说明，喷涂WC-10Co4Cr耐磨耐腐蚀涂层具有较高的拉伸结合强度和表面洛氏硬度值。与GH907变形高温合金相比，WC-10Co4Cr涂层的微动磨损摩擦系数减小了25%，微动磨损体积仅为GH907高温合金的15%。表明，HVOF喷涂WC-10Co4Cr涂层具有优异的耐微动磨损性能，促进了其在舰船动力装备上的应用，从而使合金零部件免遭受微动磨损和腐蚀损伤失效。

Abstract:

Wear resistant coatings are required to improve the wear resistant properties of many aero-engine components. WC-Co coatings are widely used for applications below 500 ℃ as the wear resistant coatings. Nonetheless， conventional WC-12Co coatings exhibit insufficient corrosion resistance in high-temperature， salt-rich marine environments， leading to premature failures in marine propulsion engines.the corrosion resistance of conventional tungsten carbide coatings， such as WC-12Co， exhibit insufficient corrosion resistance in heavy-wet， salt-rich and high temperature marine environments， leading to premature failures in marine propulsion engines. As the particles in spray flame can achieve flying rates of 600—1 000 m?s^-1 during HVOF spray process， powder particles gain a great impetus as they strike the sprayed surface of a component， resulting in highly densified and spallation resistant coatings prepared with small porosity， high hardness and tensile bond strength. Moreover， the surfaces of machined coatings are smooth， which further increase the coating wear resistance. The fine WC particles and Cr contained in the Co binder amorphous alloy can enhance corrosion resistance of the coatings and increase the service lives of worn coating components in marine environments. In this study， a high density WC-10Co4Cr wear and corrosion resistant coating with 0.63% porosity was applied upon GH907 wrought superalloy substrates， using the high velocity oxygen-fuel spraying process with oxygen and kerosene as spray fuel. Particles deposited onto the coating surface are fine， with a surface roughness（Ra） value below 2.5 μm. The coating of tungsten carbide-cobalt-chromium powders was prepared by a spray drying and sintering method. The sharp corners of angular tungsten carbide particles in the powder were locally solubilized into the melted cobalt alloy during the HVOF spray process， so that the carbide strengthening phase achieved uniformly dispersion throughout the coating. XRD analysis revealed that the coating primarily consisted of WC and amorphous cobalt solid solution alloy phases with minor W₂C. The sprayed WC-10Co4Cr wear and corrosion resistant coating possesses high tensile bond strength and surface Rockwell hardness values. The friction coefficient of the coating was decreased by 25% in comparison with GH907 wrought superalloy under the present fretting wear conditions. The averaged volume loss value of the worn coating specimens was only 15% of that of the GH907 superalloy， measured by contour measuring instruments. These results indicate that HVOF sprayed WC-10Co4Cr coatings possess excellent fretting wear resistance， promoting the application of the HVOF sprayed WC-10Co4Cr coating technology into metal components of marine vessel propulsion engines that suffer from failures due to fretting wear and corrosion damages.