热压ZrO2/MoSi2复合材料的强韧化效果与机制

用纳米尺寸的ZrO2粒子对MoSi2的增韧补强效果及其作用机制进行了初步研究和探讨.结果证明不含Y2O3稳定剂的ZrO2颗粒对MoSi2的增韧效果显著,而含Y2O3稳定剂的ZrO2颗粒的增韧效果有限.前者的增韧机制主要以微裂纹增韧为主,致使室温断裂强度有所降低;后者主要是应力诱发的相变增韧为主,故断裂韧性与强度同时得到了提高.断口分析表明复合材料中ZrO2粒子使MoSi2的断裂模式从穿晶型向准解理穿晶或沿晶型"碎化"断裂模式转变,这种断裂模式的转变与断裂韧性的提高相对应.另外还发现应力诱发相变增韧效果有限可能与基体晶粒较粗以及纳米粒子在热压过程中的团聚长大有关.

Toughening effect and mechanism within thermocom-pression composite ZrO2/MoSi2

The toughening effect and mechanism of MoSi2 by addition of ZrO2 particles with the size of nm order are investigated and discussed preliminarily. The result shows that the toughening effect of MoSi2 by adding ZrO2 particles without stabilizer Y2O3 is remarkable; the stabilizer Y2O3 mixed with ZrO2 particles, however would make the toughening effect limited. With the former, the micro-cracking plays major role in the toughening of composite and, ad a cmsequence, makes fracture strength at room temperature de- creased a little; with the latter, however, the phase transformation caused by the stress is the major origin of toughening, so that both the fracture toughness and strength are improved. Fracture section analysis shows that ZrO2 particles within the composite makes the fracture pattern of MoSi2 transformed from transgranular fracture onto quasi-cleavage transgra-nular fracture of "crushing" intergranular fracture. This sort of transformation of fracture pattern corresponds to the improvement of fracture loughness. It is also found that the phase transformation toughening caused by stress being limited may be related to the fact that the matrix grains are not sop fine and the particles with the size of nm order aggregate and grow up during the process of thermocom-pression.