Abstract
Influence of structural homogeneity of CIP-ed compacts on mechanical properties of sintered silicon carbide was investigated at the applying pressure from 100 to 700MPa. Structural homogeneity decreased with increasing pressure up to 500MPa. A compact at 700MPa showed a duplicate structure consisted of homogeneous innner parts and a surface layer with high density. Flexural strength of thin sintered plates degradated with decreasing structural homogeneity. On the contrary, the average strength of thick sintered cylinders was almost constant irrespective of the pressure. Weibull modules of the cylinders decreased with decreasing homogeneity. At 700MPa, the duplicate structure of compacts was retained in the sintered boody, resulting in the two step Weibull plot corresponding to the high-strength surface layer and the low-strength inner parts. By removing of the inhomogeneous surface layer before sintering, Weibull modulus was improved twice at 700MPa, while it was not improved at 100MPa, where the homogeneity was not improved by the removal. The highest strength and Weibull modulus were obtained for the sintered body prepared from the most homogeneous compacts with the highest green density (Pressure: 700MPa, with the surface layer removed). Fracture toughness, grain size and grain shape were not influenced by the pressure for the sintered density higher than 94%. However, there were internal defects, interconnected pores. The size of defects estimated from the mechanical properties was in the range of the size of internal defects. Temperature dependence of the maximum pore size indicated that pores grew extensively during sintering at lower applying pressure, while they were diminished at higher pressure. High CIP-ing pressure was effective to realize highly dense and homogeneous structure of sintered bodies by suppressing the inhomogeneous pore growth. Thus, the prevention of internal defects improves Weibull modulus.
