超细粉末低温超音速火焰喷涂WC-10Co-4Cr涂层及其干摩擦磨损性能

Dry Tribological Performance of WC-10Co-4Cr Coating Prepared by Low Temperature High Velocity Oxygen-Fuel Flame with Ultra-Fine Powders

为了进一步提高超细粉末WC喷涂层的性能,以5~15μm的超细WC-10Co-4Cr粉末为材料,分别采用低温超音速火焰喷涂(LT-HVOF)和超音速火焰喷涂(HVOF)技术在316L不锈钢表面制备WC涂层。通过聚焦离子束(Focused ion beam,FIB)对WC-10Co-4Cr粒子剖面形貌进行了原位切割并分析,利用SEM形貌、EDS谱和摩擦磨损试验对涂层的显微结构和干摩擦磨损性能进行了表征。结果表明:HVOF的高焰流温度使超细WC-10Co-4Cr粉末的粘结相充分熔融,WC硬质相溶于粘结相或发生脱碳,形成Cox(WC)y脆性相和W2C相,另外因Cr较低的表面张力使涂层内界面存在富Cr带,而LT-HVOF涂层没有富Cr带;LT-HVOF涂层的摩擦系数和磨损率分别为0.632 2,1.560×10-5mm3/(N·m),均低于HVOF涂层;2种WC涂层的磨损形式均以磨粒磨损为主,HVOF涂层中的富Cr带在载荷作用下形成裂纹并易于沿其扩展,造成涂层较大块剥落,降低了WC涂层的耐磨性能。

WC-10Co-4Cr splats and coatings were prepared by low temperature high velocity oxygen-fuel flame(LT-HVOF) and high velocity oxygen-fuel flame(HVOF) technology with 5-15 μm ultrafine powders as feedstock.Focused ion beam(FIB) was used to in situ cut and analyze cross section of WC-10Co-4Cr splats.Subsequently,the microstructure and dry tribological performance of WC-10Co-4Cr coatings were characterized by SEM,EDS and wear tester,respectively.Results show that the high flame temperature of HVOF process led to the sufficient melting of the binder phase in ultrafine WC-10Co-4Cr,which resulted in decarhurization of WC hard phase or dissolution of hard phase into binder to form Co_x(WC)_y and W_2 C brittle phase.Otherwise,Cr-rich strip was formed at the interface in HVOF coating due to the low surface tension of Cr melting,while Cr-rich strip was not observed in LT-HVOF coatings.Tribological coefficient and mass loss of LT-HVOF coating(friction coefficient of 0.632 2,wear rate of 1.560 × 10^(-5) mm/(N·m)) were lower than those of HVOF coating.Wear mechanisms of both WC coatings were governed by abrasive wear.In the HVOF coating,the cracks were initiated at and spread along Cr-rich strip,which caused serious coating spallation and worsened wear resistance of coating.