Influence of TixS Phases on the Strength of TiC-Mo₂C-Ni Cermets

Abstract

It was previously reported by the present authors that anomalous phases [Ti_xS(x≥1) with the dimension of about 10-50 μm] developed generally in the microstructure of commercial TiC-Mo₂C base cermets, owing to a small amount of sulfur impurity contained in the starting titanium carbide (TiC) powder. Thus, the present study was undertaken to describe the influence of TixS phases on the strength of TiC-Mo₂C-Ni cermet at room temperature. A TiC powder especially produced from TiH₂ powder and two types of commercially available TiC powders were used as starting materials. The sulfur contents of these starting TiC powders were 0.001% and 0.0390-0.042%, respectively. Three types of TiC-20%Mo₂C-20%Ni or TiC-8%Mo₂C-17%Ni alloy systems depending on the starting powders were vacuum-sintered. The carbon contents of each alloy system were minutely varied.
It was found that the transverse-rupture strength of commercial cermets was always lower than that of the other cermet prepared from the special starting powder, independent of carbon contents. The lower strength of commercial cermets was due to the fact that Ti_xS phases or larger pores were apt to operate as a fracture source. It was concluded that a small amount of sulfur impurity contained in the starting powder was detrimental to the strength of TiC-Mo₂C base cermets.