中文摘要：

基于Thermo-Calc热力学模拟软件、扫描电镜和能谱仪等实验手段,研究GH625合金铸态试样棒的显微组织,并对比讨论浇注温度对其显微组织的影响规律.GH625合金的铸态显微组织为发达的树枝晶,枝晶间可见δ相与M6C型碳化物伴生析出.一次枝晶臂间距λ1和二次枝晶臂间距λ2均随着浇注温度的升高而增大,而枝晶偏析程度则同时受扩散时间和扩散距离两方面因素的共同作用,综合相互作用导致1420℃浇注试样里Nb元素高度偏析,为枝晶间δ相的大量析出提供有利的浓度条件.因此,在制定浇注工艺时,需要综合考虑扩散时间和扩散距离的影响程度,选取合适的浇注温度（或者冷却速率）.

英文摘要：

The microstructure of as-cast GH625 alloy was investigated on the basis of experimental methods such as Thermo-Calc software,scanning electron microscopy and energy dispersive spectroscopy. The effect of casting temperature on the microstructure was also analyzed by comparing different samples. The microstructure of as-cast GH625 alloy is a dendritic structure and M6 C carbides accompanied with δ phase precipitate in the interdendritic area. Both primary dendrite arm spacing（ λ1） and second dendrite arm spacing（ λ2） increase with the increase of casting temperature; however,the microsegregation is affected by both diffusion distance and diffusion time. The comprehensive interaction of these two factors leads to the greatest microsegregation degree of Nb at 1420 ℃,which contributes to δ phase precipitation in the interdendritic area. As a result,diffusion distance and diffusion time should be comprehensively considered in making the casting process,so as to choose a proper casting temperature（ or cooling rate）.