Al_2O_3p/40Cr复合材料的热震失效机理

Failure Mechanism of Al_2O_3p/40Cr Composite under Thermal Shock

采用挤压铸造法制备了Al2O3p/40Cr表层复合材料,研究了复合材料在热震过程中裂纹萌生和扩展的机理。复合层厚度为5mm,Al2O3颗粒体积分数为56%;热震试验采用650℃保温5min、20℃水冷,反复循环。结果表明,在弱机械结合情况下,由于空气中的氧气和铁生成的氧化物与基体在热膨胀系数和弹性性能上不匹配,裂纹首先在氧化层中萌生,随着氧化层厚度增加,会加速裂纹的生长;从各个方向生长的裂纹相遇时会搭接在一起,形成比较大的宏观裂纹。此机理与WC等其他颗粒增强复合材料的热震失效机理有着显著差异。热震15次后,试验材料在复合层和基材的宏观界面出现大裂纹。

A1203 p/40Cr composite is prepared by the squeeze casting method, and the mechanism of crack initiation and expansion during the thermal shock is discussed. The thickness of A12 03 p/ 40Cr composite is 5 ram, and the volume fraction of A12Oa particles is 56%, remaining 650 ℃ for 5 minutes, then 20 ℃ water quenching in circle way. The results show that in the weak mechanical combination circumstance, oxygen likely enters the particle and matrix interface to form oxide with iron, whose coefficient of thermal expansion and elastic properties do not match with the 40Cr substrate. Firstly, crack initiates in oxidation layer, and then the oxide layer starts to become thicker and thicker, which causes to accelerate the growth of crack; on the other hand, thicker oxide can also promote crack growth. Because of the growth of cracks from all directions, the cracks finally meet and lap together to form a macro crack. This mechanism is significantly different from that of WC matrix composites during crack initiation and propagation. After 15 thermal shocks a large crack appears at macro interface of A12 03 p/40Cr composite and matrix.