MoSi2基复合材料的高温裂纹自愈合行为

Crack healing of a MoSi_2-based composite at high temperatures

采用X射线衍射、扫描电镜和三点弯曲强度测试方法研究MoSi2基复合材料Vickers压痕裂纹试样的高温裂纹自愈合行为和强度的变化。结果表明:Vickers压痕在材料表面造成明显裂纹并引起强度的急剧衰减。经过1500℃保温1h处理,在材料表面形成一层SiO2玻璃膜,材料表面的裂纹表现出良好的自愈合性能,抗弯强度恢复到345.3MPa。裂纹自愈合机理主要是高温下原子扩散作用引起的裂纹钝化和裂纹面的连接,另外材料表面SiO2玻璃层的形成也将促进表面缺陷和微裂纹的愈合。裂纹愈合是强度恢复的主要原因,而热处理对裂纹附近应力的松弛作用和表层压应力的形成也都有利于材料强度的提高。

The crack healing behavior of a MoSi2-based composite for heating element at high temperatures was investigated by X-ray diffraction and scanning electron microscopy. The effect of heat treatment on three-point bending strength of the material was also studied. The results show that the strength Of the composite reduces significantly when cracks are introduced by vickers indentation method. The composite exhibits well crack healing after heat treatment at 1500℃ for lh, and the strength recovers to 345.3MPa. A SiO2 layer forms on the surface of the composite during heat treatment. The primary mechanism of crack healing is the blunting effect of cracks tips and the interconnect of surface of cracks from the atomic diffusion at high temperature. The formation of SiO2 surface layer accelerates the healing of surface defects and microcracks, and produces compressive residual stress. The main reason for the strength recovering is crack healing. Surface and internal stress relaxation induced by heat treatment is also beneficial to the improvement of the strength of the composite.