Designing and characterization of Al-and Ta-bearing Ni-base superalloys based on d-electrons theory

Abstract

Experimental nickel-base superalloys based on commercial CM247 LC containing γ′ former elements including Al and Ta were designed on the basis of molecular orbital calculation of electronic structure. In this regard, using d-electron theory parameters, several experimental models were developed to predict γ′ solvus and γ/γ′ eutectic dissolving temperatures, volume fraction of γ′ precipitates and susceptibility to incipient melting during solution annealing. To evaluate γ′ and γ/γ′ eutectic dissolution and any trace of incipient melting, 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 metallography results showed that a decrease in θ magnitude increases γ′ solvus from 880 to 1200°C and γ′ volume fraction from 40% to about 52% in the solutionized and aged condition. The suggested model presented an incipient melt fraction (IMF) map versus Al and Ta contents to predict a safe zone from incipient melting point of view during solutionizing treatment. As a result, Al+Ta contents must be <6wt% to reach IMF<1%.