Ti(C_0.5, N_0.5)-30wt% TiB₂-Carbide系焼結体の機械的性質に及ぼす炭化物の添加効果

抄録

Hot presseed Ti (C, N)-30wt% TiB₂ ceramics have an average bending strength of 900MPa, but have a wide distribution of bending strength. The additive effects of carbide, namely ZrC, HfC and NbC, were examined in order to improve the distribution, Addition of these carbides caused that the recommendable sintering temperature is lower than that of Ti(C, N)-30wt% TiB₂ system. The addition of 5wt% HfC improved the Weibull coefficient from 8 to 12. Ti(C, N)-30wt% TiB₂-5wt% HfC materials had the Vickers hardness of 2100 and the fracture toughness K_IC of 4MPa·m^1/2. The hardness and K_IC values were same as those of Ti(C, N)-30wt% TiB₂ materials. These phenomena can be explained by the following facts. Added HfC particles react with the Ti(C, N) particles to form Ti rich or Hf rich solid solution of (Ti, Hf) (C, N). These solid solutions limit the grain growth of Ti(C, N). The lower sintering temperature of this system is also effective to suppress the grain growth. The limited grain growth makes higher transverse rupture strengths and their minimized distribution. However, no change in hardness and K_IC occurred because of the formation of Ti rich or Hf rich solid solution of (Ti, Hf) (C, N).