Solidification characteristics and as-cast microstructures of a Ru-containing nickel-based single crystal superalloy

The solidification characteristics and as-cast microstructures of a Ru-containing nickel based single crystal superalloy were systematically investigated through thermal analysis, Thermo-Calc simulation, the planar interface solidification experiment, and the directional solidification quenching experiment. The main solidification transition temperature, segregation behavior, and solidification path were analyzed, and the microstructure evolution and phase formation mechanism were also discussed. The solidification began with the formation of primary y dendrites (L -> gamma). Then Ni, Al, Ta, and Ru were enriched in the residual liquid, resulting in the precipitation of 13-NiAl phase (L -> beta-NiAl). As the beta-NiAl phase grew, the content of Ta gradually increased while the content of Al gradually decreased. Thus, the peritectic gamma' phases were precipitated on the surface of beta-NiAl phase and coarsened by the incomplete peritectic reaction (L + beta-NiAl -> peritectic gamma' + beta-NiAlResidual). The Al content further decreased and the Ta content further increased with the precipitation of the peritectic gamma' phase, leading to the formation of gamma/gamma' eutectics on the surface of the gamma dendrites or directly from liquid (L -> gamma/gamma' eutectic). Since the precipitation of beta-NiAl phase and the subsequent incomplete peritectic reaction, Cr, Co, Mo, W, and Re were rejected into the residual liquid in the vicinity of beta-NiAl phase, providing conditions for the nucleation of the TCP(R) phases (L -> R). The wide freezing range of the alloy might be the cause of the severe micro-segregation and the precipitation of some secondary phases in the interdendritic regions. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

The solidification characteristics and as-cast microstructures of a Ru-containing nickel based single crystal superalloy were systematically studied through various experiments and analysis methods. The main focus was on analyzing the solidification transition temperature, segregation behavior, solidification path, microstructure evolution, and phase formation mechanism.