Influence of carburization on the structure and properties of functional diffusion coatings based on titanium carbide on TiC-WC-Co and WC-Co alloys

摘要

The technology of applying diffusion titanium coatings from the medium of low-melting liquid-metal melts to hard alloys of the TiC-WC-Co and WC-Co types is described. It is shown that in the case of diffusion saturation of the surface layers of a hard alloy tool of the TiC-WC-Co and WC-Co types with titanium from the Pb-Bi-Li-Ti melt, preliminary carburization is an obligatory stage in the process of coating formation, and allows avoiding the formation of a decarburized zone under the diffusion layer. The effect of preliminary carburization on the phase composition of the coated hard alloy is shown. As a result of the phase analysis, it was revealed that the surface layer contains such phases as WC, TiC, Co2C, Co-C.?In this case, titanium carbide TiC is formed due to the destruction of cobalt carbide upon further diffusion saturation with titanium. In the absence of carburization, the formation of a decarbidized layer was revealed, which differs from the coating and the base in lower microhardness, the drop in microhardness is about 1000?MPa. After carburization, there was a slight increase in the hardness of the coated parts from 89?to 91 HRA. Characteristics such as the microhardness of the carburization zone and its length depend on the temperature and duration of the preliminary carburization, as well as on the elemental composition of the material to be coated. Carburization was carried out in the temperature range from 950°C to 1150°C from 30 to 120?minutes. After saturation with carbon, the thickness of the carburization zone was from 2?to 25?μm, the microhardness from 16700?to 17150?MPa for the WC-Co alloy and from 18750?to 19200?MPa for the TiC-WC-Co alloy. The hardness of the layer under the coating ranged from 27000?to 28500?MPa for the TiC-WC-Co alloy and from 19300?to 23500?MPa for the WC-Co-type alloy.