β-sialon-Al_2O_3-SiC系复相材料的高温强度和显微结构

HOT STRENGTH AND MICROSTRCTURE OF βSIALONAl_2O_3SiC COMPOSITES

研究了βsialonAl2O3SiC系列复相材料在室温至1400℃的抗折强度随温度的变化规律和显微结构。各试样的强度随温度增加而上升,并在1200℃时出现最大峰值,增强机制理解为残余应力松弛和试样表面氧化膜共同作用使其抗折强度增加。温度大于1200℃时,强度开始下降。显微结构研究显示:各温度下富SiC试样断口致密;βsialon与SiC有很好的结合强度;刚玉和碳化硅颗粒以穿晶断裂为主。富Al2O3试样中的刚玉颗粒在高温下较大的热膨胀弥合了与基质之间在中低温下存在的微裂纹间隙,有利于增加强度,其断裂形貌从低温时沿晶断裂转变到高温的穿晶断裂为主。各试样在1400℃时,仍然维持有46MPa至57MPa的高强度。

Microstructures and relationships between MOR(modulus of rupture) of βsialonAl_(2)O_(3)SiC composites and temperatures were studied.The results show that MOR of βsialonAl_(2)O_(3)SiC composites goes up depending on increases of temperatures, and reaches the maximum value at 1 200 ℃,and goes down slowly when the temperature is over 1 200 ℃. This is attributed to the enhancing mechanism of decreasing of residual thermal stresses in the composites at high temperatures and protecting functions of oxidation films on the surface of specimens. Study on the microstructure of fracture surface of specimens reveals that the bonding strength between βsialon and SiC in the composites is excellent. The intragranular fracture of SiC grains and corundum grains is dominant in some specimens.Others,micro-cracks and gaps between corundum grains and the matrix at lower temperatures can be closed by the heat expansion of corundum grains at higher temperatures, and can improve MOR of specimens at high temperatures. The fracturing style of corundum grains changes from intergranular fracture at lower temperatures to intragranular fracture at higher temperatures. Having exhibited the high compressive strength of 46 MPa to 57 MPa at 1 400 ℃, the βsialonAl_(2)O_(3)SiC composites deserve to be new promising advanced refractories.