GH4169合金真空自耗重熔铸锭显微疏松的形成规律及熔速影响

Formation Law of Microporosity in GH4169 Alloy Vacuum Arc Remelting Ingot and Influence of Melting Rate

利用金相显微镜和扫描电镜研究了熔速对GH4169合金真空自耗重熔铸锭显微疏松和金相组织的影响;采用金相图像分析软件定量分析了熔速对铸锭显微疏松数量的影响。GH4169合金真空自耗重熔铸锭显微疏松的形成规律以及熔速影响的研究结果表明,由于金属气体凝结和喷溅等原因的影响,真空自耗铸锭表面激冷层中存在大量边界粗糙曲折的显微疏松。在激冷层下方的铸锭边部组织中,显微疏松数量明显减少,边界圆滑,气泡是疏松形成的重要原因。铸锭心部显微疏松尺寸增大,倾向于沿枝晶间通道分布。铸锭心部位于糊状区的底部,由于熔池较深,凝固速率缓慢,使该处二次和三次枝晶比较发达,偏析严重,从而容易阻塞补缩通道,所以易形成沿枝晶间通道分布的大尺寸疏松。随熔化速率增大,枝晶倾向于水平生长,熔池加深,二次和三次枝晶更加发达,偏析更加严重,显微疏松的尺寸和数量显著增加。

The effects of melting rate on the microstructure and microporosity formation of GH4169 alloy VAR（vacuum arc remelting） ingots have been studied by using metallographic microscope and scanning electron microscope,and its effects on the area percent of microporosity of the ingots was also analyzed quantitatively by the metallographic image analysis software.The results show that the microporosity formed in the chilled layer at the surface of the ingot possesses a harsh surface due to the existing of metal particles on the mold caused by sputter or vapor coagulation.The micropores formed at the edge part under the chilled layer tend to appear with a round shape and smooth surface,and hence it might inherit the shape of pores formed by the ease of gas element such as N from the liquid.The pore size is small and its density is largely reduced compared with that in the chilled layer.In the centre of ingot,the size and density of the microporosity are greatly increased,which is distributed along the interdendritic area,because the elements congregation here is serious and the secondary or tertiary dendrites are well developed which blocks the liquid passage.With the increasing of the melting rate,the formation of the microporosity especially at the center of the ingot is increased significantly,because the depth of the liquid pool is increased,the dendrites tend to grow horizontally,the secondary and tertiary dendrites are developed further,and the elements congregation is more serious.