材料期刊网

本文对国内外关于高温合金铸件表面晶粒细化机理的几种观点作了验证;用X射线,显微镜和电子探针法对效果不同的型壳作了分析,发现铸件晶粒的细化与铝酸钴的分解以及合金中的活性元素有关;从浇铸后的型壳表面、铸件表面以及铝酸钴粉加不同活性元素的真空加热后的产物中均发现了Co(高温型)粒子。本文也做了铝酸钴加Al粉的真空差热分析并作了热力学计算,证明Co粒子的生成并不伴随着吸热,实际却是一个不大的放热效应。综合诸实验,作者认为铸件表面晶粒细化主要是由于Co粒子的核心作用;据此也探讨了合理的工艺,并巳用于工厂生产中,效果显著。

The mechanism of the surface grain refinement for superalloy castings has been investigated by examination of some recent allied approaches and by observations on the investment molds of various effectiveness using X-ray diffraction, microscopy and EPMA. It was identified that the grain refinement of the castings is dependent upon the decomposition of cobalt aluminate and the active alloying elements contained in the alloy. After the alloy casted, the isolated particles of high temperature type cobalt were found on the surfaces of the investment mold and the castings, as well as the products of the mixture of cobalt aluminate together with different active elements heated under vacuum. Both the vacuum DTA of cobalt aluminate mixed with Al powder and the thermodynamical estimation of the reaction may confirm that the formation of Co particles did not accompany with an endothermic peak as formerly expected, but, in fact, a small exothermie effect was observed. It seems that the surface grain refinement of the castings is mainly due to the nucleation of the cobalt particles produced during casting. Thus, a rationalized process proposed has already been put into industrial practice with remarkable results.