A solidification diagram for Ni-Cr-Mo-Gd alloys estimated by quantitative microstructural characterization and thermal analysis

A γ-Gd solidification diagram is proposed as an aid to understanding solidification behavior of Ni-Cr-Mo-Gd alloys. In this system, the Ni-Cr-Mo solid solution γ primary austenite phase is treated as the “solvent” and Gd is treated as the solute. The proposed diagram, which has features characteristic of a binary “eutectic” system, was constructed by combining differential thermal analysis and quantitative microstructural analysis data. As a result of the partially divorced solidification microstructure in the ingots studied, determination of the fraction eutectic, and hence the eutectic composition, requires the use of advanced image analysis techniques. The diagram displays a number of features that are very similar to the Ni-Gd binary system and can be used to assess the influence of the Gd concentration on solidification behavior.