常圧焼結炭化ケイ素の破壊強度および破壊じん性値の温度依存性について

抄録

In order to clarify the temperature dependences of fracture strength and fracture toughness of sintered silicon carbide, the fracture strength and fracture toughness tests were carried out under 3-point bending conditions at the temperature range up to 1500°C in air and in vacuum. The single edge precracked rectangular bar specimens were used in the fracture toughness tests. The fracture strength in air exhibited a maximum value at about 1200°C. On the other hand, the fracture strength in vacuum and the fracture toughness in air and in vacuum increased monotonically with an increase in temperature. The increase in fracture toughness at elevated temperature in air is attributed to healing due to the oxide, SiO₂, formed on the precracked surface. To evaluate the effect of healing on fracture toughness, the precracked specimens were post heat-treated at several elevated temperature levels, and then the fracture toughness tests were conducted on these specimens at room temperature. The results revealed that the higher was the annealing temperature, the higher was the fracture toughness depending on the healing of the precracked surfaces.