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晶界脆化问题一直是提高金属材料服役性能所必须关注的重要问题,但目前并没有直接的实验方法来确定晶界的硬度,因而也无法直接判定晶界的脆化状况。以经过不同工艺热处理的Ni-Bi二元合金为研究对象,利用光学金相显微镜和透射电镜观察了合金的微观组织,同时利用纳米力学探针进行了合金晶界和晶粒基体载荷—位移曲线的测定,并计算出了晶界和晶粒基体硬度的变化规律。结果表明,Ni-Bi二元合金的晶界和晶粒基体都不存在沉淀相;晶界硬度要低于晶粒基体的硬度,而且时效时间较长的合金,其晶界硬度更低。由此,确认了纳米力学探针在测量晶界脆化方面的可行性,并分析确定了晶界软化的原因:Bi的晶界偏聚。
The problem of grain boundary embrittlement has always been an important issue that must be paid attention to in improving the serviceability of metallic materials. However, there is no direct experimental method to determine the hardness of the grain boundaries and therefore the grain boundary embrittlement can not be directly determined. The Ni-Bi binary alloys which have been heat-treated by different processes were studied. The microstructure of the alloy was observed by optical microscope and transmission electron microscope. Meanwhile, the grain boundary and load-displacement curve The changes of grain boundary and grain matrix hardness were calculated. The results show that the grain boundary and the grain matrix of Ni-Bi binary alloy do not exist as precipitates; the grain boundary hardness is lower than the hardness of the grain matrix, and the grain boundary hardness of the alloys with longer aging time is lower. Thus, the feasibility of nanomechanical probe in the measurement of grain boundary embrittlement was confirmed, and the reason for the softening of the grain boundary was confirmed: the grain boundary segregation of Bi.