Solidification of a modified inconel 625 alloy under different cooling rates

Abstract

The solidification characteristics of a modified version of Inconel 625 alloy were studied under non-equilibrium conditions. To achieve this, samples were melted and then solidified under cooling rates ranging from 0.1 K/s to 8000 K/s using a modified DTA, a mirror furnace and levitation casting. Features such as solidification interval and latent heat of fusion were obtained from the cooling curves. The segregation patterns of a number of alloy elements were analysed as well as the amount of the different phases found in the microstructure. Three reactions were observed in the DTA thermographs, i.e. precipitation of austenite, niobium carbides and Laves eutectic. The measured latent heat of fusion is not constant along the solidification process. Lower values of latent heat of fusion were measured as high cooling rates. The segregation behavior of the different solute elements indicates that the cooling rate promotes higher concentrations in solid solution. The amount of secondary phases decreases with increasing cooling rate. A theoretical explanation is given in terms of lattice defects formed in the solid and their interaction with the solute atoms.