微尺度铸件室温蠕变性能的微尺度效应

Microscale Effects on Creep Properties of Microcastings at Room Temperature

采用微金属型精密铸造工艺制备的微齿轮铸件整体尺寸在微米量级,无法进行常规拉伸蠕变试验。采用高精度的纳米压痕仪测试室温下微铸件的蠕变特征,基于压痕做功概念确定蠕变应变速率敏感指数m,结果表明:在微铸件齿顶和齿根处都获得了负的m值,分别为-0.13451和-0.12346,而宏观常规铸件的m值为0.40365,微铸件表现出明显的"微尺度效应",分析认为,微铸件快速凝固导致大量的Al原子以过饱和的形式固溶到Zn基体中,在压痕试验过程中Al原子作为溶质原子以管道机制扩散并钉扎位错,导致了动态应变时效(DSA)效应。

The overall size of the microcasting prepared is in the range of micron, whose creep behavior cannot be measured through conventional tensile creep test. Its creep characteristics at room temperature are measured by Berkovich nanoindentation tests of high precision. Then based on the concept of ＂work of indentation＂, the strain rate sensitivity of creep （m） is obtained from the load-depth curves. The results show that the m obtained in the top and root are -0.134 51 and -0.123 46 respectively. Whereas m in conventional castings is 0.403 65, and the obvious micro-scale effect are found. It is analyzed that massive A1 atoms induced by rapid solidification of micro-castings are solid solution existing in Zn base in the form of supersaturation. In this experiment, A1 atoms used as solute atoms are diffused by pipe diffusion, then pin dislocations. This results in dynamic strain aging （DSA）.