Prediction of Incipient Melting Map and γ’ Features of Ni-Base Superalloys Using Molecular Orbital Method

Experimental nickel-base superalloys based on commercial CM247 LC containing Al and Ta were designed at a constant total Ta + W content (in wt%), on the basis of Molecular Orbital calculation. The γ’ solvus, γ/γ’ eutectic dissolving temperatures and susceptibility to incipient melting during solution annealing were predicted using this method. Solutioning and aging treatment were carried out following Cannon-Muskegon Corporation indication. For simplifying the model, Md and Bo parameters were replaced by a new electronic parameter (θ) named alloying angle. DSC thermal analysis and quantitative microstructural evaluations showed that a decrease in θ magnitude increases γ’ solvus and γ’ volume fraction considerably in the solutionized and aged condition. Also an incipient melt fraction (IMF) map versus Al and Ta contents was presented to predict a safe zone from incipient melting point of view during solutionizing treatment. As a result, Al + Ta contents must be less than 6 wt% to reach IMF < 1%.