单晶钨高温长期服役下的显微组织演变行为

Microstructure Evolution of Single Crystal Tungsten Serving Under High Temperature for Long Time

本文利用电子背散射衍射技术(EBSD)以及金相显微技术研究了热离子能量转换器发射极表面单晶钨涂层高温下服役1 000h的显微组织演变行为。研究结果表明,化学蚀刻后单晶钨涂层的蚀刻形貌与晶面指数具有一一对应关系,{110}晶面表面为平行排列的台阶结构,{112}晶面表面为较为规则的立方体形,且层层相叠。服役后发射极单晶钨涂层表面蚀刻形貌沿轴向存在不均匀现象,与中间部分相比,端部蚀刻形貌保持相对完整。在发射极单晶钨涂层表面观察到小晶粒带,小晶粒平均尺寸约为200μm。也出现一些棱角不太分明没有完全突出且尺寸较小的亚晶,小晶粒尺寸比亚晶尺寸大。小晶粒表面指数并不是唯一的,没有明显的择优取向,但小晶粒和基体的取向差角均小于30°。

The microstructure evolution of single crystal tungsten working at high temperature for 1 000 hwas investigated using optical microscopy method in combination with electron backscatter diffraction(EBSD)technique in this study.The experimental results show that different crystal planes correspond with different specific etching morphology.The etching morphology of{110}crystal plane consists of parallel stepped structure and the etching morphology of{112}crystal plane consists of stacked cubic structure.The etching morphology of single crystal tungsten along the axial direction after serving is not uniform.Compared with the center zones,the etching morphology at the end zones of the emitter has remained relatively intact.In addition,small grains were observed along the axial direction and the average grain size of them was about200μm.Some subgrains whose edges were not clear were also observed.The grain size of the small grains is larger than that of the subgrains.Surface indices of all small grainsvary from each other and show no apparent preferred orientation.However,all the misorientation angles between the small grains and matrix were analyzed and the results show that they are all smaller than 30°.