Functionally graded cemented tungsten carbide with engineered hard surface and the method for making the same

A method of preparing a functionally graded cemented tungsten carbide material, the method comprising:

• obtaining a sintered cemented tungsten carbide material including tungsten carbide and a metal binder, the sintered material being homogeneous and substantially free of complex carbides and η phases prior to subsequent heat treating, and having an initial nominal value of the metal binder;
• heat treating the sintered material via a controlled diffusion process that includes:
• forming a carbon gradient by heating the sintered material to a liquid binder region within a liquid binder temperature range in which liquid metal binder, but no solid metal binder, coexists with tungsten carbide, said heating being maintained for a first holding time to form a carbon gradient having a depth of diffusion;
• and
• subsequently forming a metal binder gradient by step-wise heating the sintered material to a multi-phase non-equilibrium state within a multi-phase temperature range in which liquid and solid binder phases coexist and wherein the multi-phase non-equilibrium state includes solid tungsten carbide, liquid metal binder, and solid metal binder, said step-wise heating being maintained for a second holding time sufficient to allow migration of liquid metal binder across the depth of diffusion to form the metal binder gradient;
• and
• cooling the sintered material at a predetermined time to preserve the functionally graded cemented tungsten carbide having a surface layer with lower content of the metal binder than that of a final nominal value of the metal binder in a bulk of the functionally graded cemented tungsten carbide.