中子衍射法研究单晶镍基高温合金热机械疲劳引起的应力和晶格错配

采用中子衍射法对热机械疲劳后的单晶镍基高温合金样品内部中心点进行了实验测量，数据处理采用了双相叠加峰和单峰分析两种方法，计算得到了样品材料的宏观等效应力、应力偏量、γ相和γ′相的等效应力和晶格错配度等.实验结果表明，两种分析方法得到的宏观等效应力基本一致.在热机械疲劳循环100周出现最大宏观等效应力和应力偏量，此时位错等微缺陷达到饱和，偏离中心点处γ′相应力减小显著；在热机械疲劳开始阶段负错配度明显减小，随循环周次增多基体塑性应变累积又使负错配度以每次81×10^-6的速度逐渐线形增大. 关键词： 中子衍射 单晶高温合金 等效应力 应力偏量

Neutron diffraction study of stress and lattice mismatch induced by thermo-mechanical fatigue in single crystal superalloys

The center points of the thermo mechanical fatigued single crystal Ni based superalloys were measured by neutron diffraction and the results have been treated in two methods: two overlapped peaks and a single peak. The macroscopic equivalent stress, deviatoric stress components, γ/γ′ phase equivalent stress and lattice mismatch are determined according to the experimental results. The stress results show that the macroscopic equivalent stresses are basically consistent when using two analysis methods, the maximum of macroscopic equivalent stress and deviatoric stress components appeared at thermo mechanical fatigue that of 100 cycles, and at this point, the micro defects， such as dislocations, are saturated and the stress of γ′ phase away from the center was reduced remarkably. The calculated results also indicate that the negative lattice mismatch is reduce markedly at the beginning of the thermo mechanical fatigue. Subsequently, it increases linearly with the fatigue cycles at the speed 81×10^-6 per cycle because of the accumulated plastic strain in the matrix.