Effect of post-sintering heat treatment on mechanical properties and microstructure of SiC-TiB_2 composites

摘要

Dense SiC-TiB_2 composites with 24 vol% TiB_2 were fabricated by pressureless sintering at 1940℃. Al_2O_3 and Y2O3 were used as sintering additives to create a liquid phase and promote densification. TiB_2 was formed by an in situ reaction between TiO_2, B_4C and C. The sintered samples were subsequently heattreated at temperatures ranging from 1850°C to 2000°C. The effect of temperature of post-sintering heat treatment on microstructure and mechanical properties of the SiC-TiB2 composite was presented. Heat treatment at 1970℃ considerably improved the strength and the fracture toughness of sintered samples while maintaining high density. The elongation of α-SiC grains during the heat treatment was found to be responsible for an increase in fracture toughness. The presence of liquid phase assisted the elongation of grains which, in turn, activated crack bridging and crack deflection toughening mechanisms. Maximum strength of 540 MPa was found to be the result of improved fracture toughness. Heat treatment at temperatures above 1970℃ led to a deterioration of mechanical properties.