Preparation of Ti(C,N)-WC-TaC solid solution by mechanical alloying technique

Mechanical alloying (MA) is a dry, high energy ball milling process for producing composite metallic powders with a fine controlled microstructure. Traditionally, the raw materials used in MA must include at least one fairly ductile metal to act as a host or binder to hold together the other ingredients. MA is believed to occur by repeated welding and fracturing of a mixture of metallic and nonmetallic powders in a highly activated ball charge. Reported here, however, is a study of the mechanical alloying process of all ceramic phases, i.e., Ti(C_0.3N_0.7) + WC + TaC. The three ceramic powders were mixed in weight proportion of 70:20:10 and milled in a planetary ball mill at a ball-to-powder weight ratio of 20:1. X-Ray diffraction examinations were performed after MA for different time. It was found that TaC peaks progressively reduced in intensity with milling time and disappeared after 88 hours. Though there was an over-all peak intensity drop for every species, WC peaks persisted and remained well defined. The half-peak-width of the powders increased significantly after MA indicating decrease in the coherent crystalline domain size. Pycnometry density measurements of the mechanically alloyed powders indicated that the density of the powder mixture decreased with milling time. Energy Dispersive X-Ray (EDX) studies showed that Ti, W, Ta all exist in the same particle after 131 hours of milling, indicating progress of the solid solution process. Hard phase solid solution of carbonitride of Ti, Ta, W is a source powder in making high toughness carbonitride cermet cutting tools. Success in producing this hard phase solid solution by Mechanical Alloying opens up a whole new avenue in cermet cutting tool industry.