Microstructure and Segregation Behavior of Rene88DT Alloy Prepared by ESR-CDS

Abstract Directionally solidified Rene88DT alloy ingots were produced by electroslag remelting continuous directional solidification (ESR-CDS) technology. The as-cast structures of ESR-CDS Rene88DT alloy ingot were analyzed by optical microscopy (OM), field emission scanning electron microscopy (FESEM) with energy spectrum and transmission electron microscopy(TEM), and simultaneously compared with conventional ESR ingot. The results show that the region of the severe central segregation existing commonly in the conventional ESR ingot is eliminated in the ESR-CDS Rene88DT alloy ingot, because the above segregation is formed in the intersection of interfaces among columnar crystals and equiaxed crystals or between columnar crystals each other. In addition, the ESR-CDS Rene88DT alloy ingot shows smaller secondary dendritic spacing and smaller non-equilibrium precipitates phase. Due to the decreasing micro-segregation level, the uniform distribution of alloy elements can be achieved when Rene 88DT alloy is subjected to the heat treatment at 1200 °C for 24 h. Statistical results of inclusions reveal that the maximum size of inclusion in the ESR-CDS Rene88DT alloy is not more than 5.89 μm and the inclusion volume reduces by over 60% compared with conventional ESR and P/M, respectively. The hot working plasticity of directionally solidified Rene88DT superalloy can be improved, which provides a basis for implementation of cast-and-wrought (C&W) route.