2008 年 49 巻 3 号 p. 624-628
0–25 mass% of ∼2 um and ∼20 um TiC powders are added to vanadium and chromium containing steel powders to form metal matrix composite tool steels. The metal and ceramic powders are encapsulated and hot isostatically pressed for densification. Their density and mechanical properties are characterized. Product densification of over 99.9% theoretical density is achieved. Its hardness is found to increase with the amount of TiC addition. Product with over HRc65 hardness is obtained with addition of 25 mass% coarse TiC particles in which the matrix and strengthening particles intermix uniformly. The fine TiC particles distributed as packs at the intergranular regions of the matrix phase and give less hardening effects. The flexural strength is reduced by TiC addition regardless of TiC particle size, because the flexural strength is controlled mainly by crack initiation and less by crack propagation. For impact test, brittle fracture is induced by high strain rate which initiates the cracks with ease in both matrix and hard phases. The impact toughness is thus increased slightly with TiC showing fine particles are more effective in blocking crack tip propagation in high strain rate testing condition.
