The invention belongs to the field of hard
alloy preparation, and in particular relates to an ultra-fine
crystal gradient
alloy with a rich-
cobalt surface and a preparation method of the
alloy. According to the ultra-fine
crystal gradient alloy with the rich-
cobalt surface, a gradient layer with the rich-
cobalt surface, which is 10-40mu m thick, is formed by taking WC (Wolfram
Carbide) and cubic phase carbonitride as a core part hard phase and cobalt as the binding phase, wherein the
average size of the
crystal particles of WC in the hard phase and the gradient layer is 0.2-0.4mu m, the content of cobalt in the gradient layer with the rich-cobalt surface is 1.2-2 times of the standard content of cobalt of hard alloys, and the gradient layer with the rich-cobalt surface is free of the cubic phase carbonitride. The preparation method comprises the following steps: firstly, preparing the materials, wet-
grinding and pressing into a material blank, and supplying an
inert gas with the pressure of 5-10MPa before reaching a
liquid phase sintering temperature, wherein the
liquid phase sintering temperature is 1,350-1,500 DEG C. By charging the gas with certain pressure in the
liquid phase sintering period, the ultra-fine crystal gradient alloy with the rich-cobalt surface is prepared, the WC crystal grains are refined, a rich-cobalt
surface layer of certain thickness is obtained, the sintering period is shortened, and the production cost is lowered.