热挤压态SiC_P-LY12复合材料的超塑性变形

SUPERPLASTIC DEFORMATION IN EXTRUDED SiC_P-LY12 COMPOSITE

未经任何热处理的热挤压态SiC_P-LY12复合材料在基体固相点附近获得超塑性变形,在温度495～510C、应变速率2×10^(-4)s^(-1)时,终断延伸率大于150%。对试验数据的分析表明,在前述变形参数范围内,复合材料的变形机制发生了变化,使终断延伸率显著升高,但复合材料超塑性变形过程的应变速率敏感性指数(m)在同一温度下的m值随应变速率降低而逐渐增大,其最高值并未对应于最大延伸率;同时,应力-应变曲线在通常的动态再结晶阶段后出现一个独特的应变硬化阶段,直至最终断裂。微结构观察发现,变形初期复合材料即发生动态再结晶,据此推测,前述异常硬化阶段可能与再结晶组织的长大有关。另一方面,SiC_P-Al界面在变形过程中严重弱化,成为裂纹优先扩展的路径,不利于获得高的延伸率。

Superplastic deformation was found in extruded SiC_p-LY12 composite without any refining treatment. Maximum elongation above 150% was achieved at temperatures of 495510℃ and initial strain rate of 2×10^(-4)s^(-1). Analysis of test data indicates that there is a transition of deforming mechanism near the optimum parameters, which leads to a significant increase in elongation to failure, while the value of strain rate sensitivity (m) of superplastic composites increases with elevating temperature or decreasing strain rate; however, the maximal value of m seems not corresponding to the highest value of elongation. A unique strain-hardening stage took place after the ordinary dynamic recrystallization stage and endured to failure. Microstructure observation found that dynamic recrystallization occurs in the initial stage of deformation, which hints that the unique strain hardening phenomenon might be related with recrystallized grain growth. Furthermore, interfaces between SiC particles and matrix were severely weakened during deformation and turned to be a preferential path of crack propagation, which is harmful to achieving high elongation.