Stainless Steel Surface Coating Of Wc-ni-based Alloy Coating

Wear always lead to severe losses of the materials surface in engineering practice .Thermal spraying technique ,which is an important surface treatment technology, can be used to strengthen and restore material surface with coatings .This technology can also endow material surface with particularly performances at the same time .So this technique has been widely used in industry.In this dissertation ,WC-Nickel base alloy composite coatings were successfully prepared on the stainless steel substrate by general oxy-acetylene flame spraying fusion.The microstructures and components of the coatings were studied by means of optics microscope (OM) and X-ray energy dispersive spectrometer (EDS) respectively; The surface morphologies of abrasive samples and spraying powders were analysed with scanning electron microscope (SEM); The hardness of the coatings and substrate were measured with Rockwell indentation hardness sclerometer .The wear resistance of the coatings and the substrate were compared by self-made abrasive equipments. Meanwhile the parameters of spray-fluxing were optimized through the research on the effect of coating thickness and cooling modes on the performances of the coatings.The coating phase composition is composed ofγ-Ni solid solutions and large amounts of reinforced phases. Strip-shaped distributing pores and inclusions mainly exist at interfaces between two spray-welding layers and accumulate in excessive WC areas .Coating elements are badly segregate in microcosmic region ,while they are well distributed in macroscopical region , Partical dissolution of WC particles occurs during spray-welding process .Obvious diffusion of alloy elements is found at the interface between coating and substate, and the metallurgical bond is achieved.As compared to the substrate, the coating has higher surface hardness and better wear resistance. Average surface hardness of the coatings is twice higher than the substrates,and surface hardness of the cooling coating is slightly higher than the slowly cooling coating .When the coating thickness is less than 1mm ,the surface hardness linearly correlates with thickness ,besides the slope is over 1;The value of surface hardness becomes stable and reaches design value when thickness is more than 1mm. From coating to substrate, there is a gradual change region of hardness value distribution from big to small.Adopting the indexes of weight loss and volume loss,the relative wear resistance of the air cooling coating is 3.91 times and 5.00 times higher than the substrate,and the slowly coating is 2.42 times and 3.81 times higher than the substrate.Therefore optimized parameters of spray-welding are that the coating is dealed with air cooling,whose thickness is controlied about 1mm.Surface morphologies of abrasive wear of grains indicate that the frictional marks of the substrate are wide,deep,straight and dense,therefore the wear mechanism of the substrate is micro-plowing and plough effect. But the frictional marks of the coatings are narrow,shallow,incontinuous and sparse, so the wear mechanism of coatings is micro-plowing and micro-peeling. Additive WC reinforced phases and manifold self-generating reinforced phases effectively resist abrasive wear of grains,but the peeling of WC is main facto(?) of invalidation of coatings.