An investigation on as-cast microstructure and homogenization of nickel base superalloy René 65

Abstract

Abstract Nickel base superalloy René 65 is a cast-wrought derivative of René 88DT. Lower cost and comparable physical properties allow René 65 to serve as a promising candidate material for turbine disks in next-generation aeroengines. The cast-wrought route leads to significant segregation of solute elements during solidification of René 65, which should be reduced by a proper homogenization scheme. We use René 65 samples from a Ø 450 mm electros-slag remelting ingot (sample Disk I) and a Ø 250 mm pilot vacuum arc remelting ingot (sample Disk II) to investigate as-cast microstructure and homogenization schemes of the alloy. It is discovered that γ–γ′ eutectic phase, borides–carbides, and TiN are the major precipitated phases in as-cast René 65 and Ti, Nb, Mo, and W are the critically segregated elements. The temperature too high to homogenize René 65 is found to be ≥1,190°C due to defect generation and straightening grain boundaries, whereas 1,140°C is too low due to undissolving γ–γ′ eutectic phase. The acceptable temperature among the selected temperatures is found to be 1,160°C. Thermal compression using homogenized samples reveals that in Disk II 1,160°C for 50 h provides the lowest flow stress. Estimation based on kinetics predicts that the equivalent deformation effect in Disk I is obtained at 1,160°C for 82 h.