Fracture toughness of ceramics at elevated temperature and metallurgical factors for controlling the toughness

点击翻译按钮获取中文摘要

Three-point bend tests of four kinds of silicon nitrides with the same chemical composition, which were produced by different sintering methods and under different sintering conditions, were carried out at elevated temperature. Effects of sintering method and density on fracture strength were investigated. Effects of sintering method and density on fracture toughness evaluated by using the indentation method and fractographic method were also investigated. A new method for evaluating fracture toughness of ceramics, where fatigue precrack was introduced at elevated temperature, was developed. Main results are summarized as follows.(1) Fracture strengths were decreased with reducing density. The Weibull modulus m seemed to depend upon the sintering mehtod. (2) Fracture toughness values and also the Weibull modulus m were decreased with reducing density. (3) Fatigue precrack was successfully introduced into a notched bend specimen of silicon nitride at 1200゜C. The fatigue precrack specimen satisfied the conditions for fracture toughness specimen required by the standard of ASTM E399. (4) Fracture toughness values obtained by fatigue precracked specimens were almost equal to those obtained by using the indentation method. Fracture toughness malues up to the temperature of 1000゜C were almost the same as those at room temperature.