热压氮化硅在1200℃的高温疲劳损伤

FATIGUE FAILURE OF HP Si_3N_4 AT 1200℃

研究了热压氮化硅陶瓷的室温和高温力学性能及在１２００℃的高温疲劳损伤行为，发现材料的弹性模量、抗弯强度与断裂韧世均随温度升高而下降，但在１０００℃以上降低最为显著。在１２００℃高温疲劳寿命与应力之间符合单对数线性关系，经分析发现这种现象与失效的热激活过程有关。通过对实验数据、ＸＲＤ相结构、变形动力学过程和断口的微观分析证明，陶瓷高温疲劳失效机理为“杂质空穴复合作用机制”。对热压氮化硅来说，失效机理主要是杂质促进晶界非晶相软化、产生晶界滑动和晶内晶界变形不协调，从而导致开裂。

The mechanical properties at room temperature and high temperature and fatigue behavior of HP-Si_3N_4 at 1200℃ are investigated.It is found that the Young’s medulus,bending strength and fracture toughness decrease with the increase of temperature and this decrease is more apparent when the temperature is above 1000℃,There is linear relation between the stress and the logarithm of static fatigue fracture life,due to the fact that the failure is related to thermal-activation. Through the analysis of the experimental data,XRD,micro-defor-mation dynamics and the observation of fractographies,it is proposed that the fatigue failure mechanisms of ce-ramics at elevated temperature are the combined effect of impurity and cavity. As for HP-Si_3N_4,the failure pro-cess is the softening of the glass phases of grain boundary accelerated by impurity, so that slipping of grain boundaries occurs resulting cracking along grain boundaries.