Determination of the solidification curve of a RENE N4 superalloy

Abstract

The knowledge of solidification curves is essential for the control of casting processes. Efforts have been conducted in calculating the solidification curves by using thermodynamic models. However, for a nine-component alloy such as the RENE N4 Ni-based superalloy, a complete thermodynamic description of the system involves too much work and is almost impossible. The nominal composition of the superalloy is Ni-9 wt pct Cr-7.5 wt pct Co-6 wt pct W-4.2 wt pct Ti-4 wt pct Ta-3.7 wt pct Al-1.6 wt pct Mo-0.5 wt pct Nb. Chen et al. proposed a methodology to estimate the free energies of the related liquid and solid phases from the free energies of the constituent binary systems, and then they used the theoretical phase relationships and the Scheil model to calculate the solidification curves of the superalloy. The results were successful; however, the evaluation of the free energies of the related phases of the 36 binary systems was still an enormous amount of work. A different approach to the determination of the solidification curve has been proposed. This method has been tested for various aluminum alloys and has been demonstrated to be successful. This method uses differential thermal analysis (DTA) to determine the cooling curvemore » of the alloy, and then the solidification curve is derived from the experimentally determined cooling curve based on a heat transfer model of the DTA. this DTA method was used in this study to investigate the solidification curve of the RENE N4 superalloy.« less