Study on surface durability of thermally sprayd WC cermel coating in rolling sliding contact

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In the present invesitigation, using a two-roller testing machine, the authors examined the surface durability of thermally sprayd WC-Cr-Ni cermet coating in lubricated rolling or rolling with sliding contact. The coatings of about 40 mum or 90mum thickness were formed by high velocity oxy-fuel flame spraying (HVOR) onto the shot-basted substrata made of a mormalized steel, a thermally refined carbon steel or a carvurized alloy steel then the surfaces after spraying were finished smooth to a mirror-like condition. Mating the WC cermet coated steel roller with the carburized steel roller without coating, the effects of rolling sliding conditions, coating thickness, substrate hardness, etc.were examined. Furthermore, the elastic-plastic behavior of the subsurface layr was analyzed and the effect of subsurface material on the durability of coated roller was descussed. The results obtained are summarized as follows.1.The durability of coated roller varied remarkably depending on the substrate material. Namely, the normalized steel with a hardness of about 200 Hv and the thermally refined steel with a hardness of about 320 Hv showed a shorter life a than the carburized steel with a hardness of about 760 Hv.2.In pure rolling conditions, the coated roller exhibited a fairly high durability. In rolling/sliding conditions, flaking was apt to occur when the coated roller was placed on the slower (driven) side, while flaking was restrained when the coated roller was placed on the faster (driving) side.3.Time to flaking increased as the coating thickness increased ; especially, the effect appeared more distinctly when the substrate hardness lowered.4.From the results of elastic-plastic analysis of the subsurface layr, it was confirmed that such a distinct feature in the occurrence of flaking due to the substrate hardness is attributed to the difference in the plastic deformation of the substrate.