Change in the Surface Microstructure of Ti(C_0.5N_0.5)–20WC–10Ni–10Co Cermets During Sintering in a Nitrogen Atmosphere

Abstract

Experiments were carried out to determine the effects of introducing nitrogen during sintering on the formation of the surface gradient zone for Ti(C,N)‐based cermets. WC was used as a secondary carbide in a Ti(C,N)–Ni/Co system, and processing was carried out in vacuum, and under various nitrogen conditions (at 1torr). Nitrogen was introduced during various stages of the sintering (above 1300°C). The introduction of nitrogen during the heating stage facilitated the formation of a (Ti,W)(C,N)‐enriched layer to a greater extent than the vacuum conditions. A thermodynamic calculation revealed that denitrification occurs during sintering, even when nitrogen pressure is applied. A nitrogen atmosphere during the heating stage is effective in retarding the dissolution of WC in the cermet matrix. The introduction of nitrogen during the holding or cooling stages also led to an enrichment in the binder phase near the surface. The thickness of the stratified binder layer was strongly related to the cooling rate.