Elevated temperature behavior of sintered silicon nitride under pure tension, creep, and fatigue

Pure tensile fast fracture, tensile creep, and tensile cyclic fatigue/creep interaction data are reported for GTE SMW-1000 sintered silicon nitride (Si₃N₄) which is being investigated as a candidate material for advanced heat engine applications. Pure uniaxial tensile tests conducted at room temperature and at elevated temperatures indicate that the tensile strength of this material was retained to 1100°C, above which there was a sharp decrease in strength. Tensile creep tests performed at 1100°C and 1200°C showed that the steady state creep rate was dependent on both the temperature and the applied stress, the effect of temperature being more dominant than the applied stress. Further, creep induced deformation by linking of small pores, and changes in the chemical contents were observed. The effect of cyclic loading on creep, and residual tensile strength were also studied at 1200°C. Test results showed that precycling can dramatically increase creep resistance. Cyclic loading at 1200°C also increases the strength of the material.