مقاومت به گسترش ترك در دماهاي بالا و نقش ارتباطي آن با مقاومت به شوك و خستگي گرمايي

Thermal Stress Resistance to Fracture and its Relation to with Resistance to Thermal Futigue and Shock

Dense Silicon nitride was investigated to determine the effect of its microstructural parameters and densification on thermo-mechanical properties and thermal stress resistance to fracture initiation during a hot or cold mechanical and thermal shock testing. The different materials and microstructures were obtained by changing the parameters such as the type of the powder, additive, forming process and sintering condition. Maximum crack growth and thermal shock resistance of dense Si? Vs are achieved after complete conversion of the a->B transformation, and after the change in grain morphology towards elongated grain and the relative crystallization of the second phases have been obtained. The characteristics are obtained by a high a phase content of the starting powder, high Y203, and sintering condition of higher temperature (2000 C), longer soaking times (Ih) and load application at the beginning of the thermal cycle.