Accelerating the discovery of novel γ/γ' Co-based superalloys by probing temperature and alloying effects on the γ' precipitates

Abstract

The discovery of γ/γ’ Co-based alloys has set off a great wave of searching advanced high-temperature materials. However, finding appropriate compositions to acquire the γ’ phase is a challenge in metallurgical experiments. We first perform a systematic investigation of temperature-induced entropy contributions to the stability of a series of γ’ Co3(Al, TM) (TM = W, Ti, Mo, V, Nb, Ta, Re, Cr) phases. The results suggest that the finite-temperature induced entropy terms govern the thermodynamic stability of Co3(Al, TM). The scale of individual entropy contribution is obviously different for each Co3(Al, TM). The metastability of Co3(Al, TM) is drawn as: W > V > Cr > Nb > Ta > Re > Ti > Mo. We elucidate the foregoing observations and extend to identify one potential γ/γ’ Co-Al-Nb system. Probing into the further quad-alloying effect on stability, it is confirmed that the experimental observed γ’-Co3(Al, Nb, Mo) originates from the stabilization of >4 at.% Mo which weakens the engagement of Nb in electronic hybridizations. Moreover, both >1.5 at.% Ta and > 3.0 at.% Ni promote the stability of Co3(Al, Nb) phase. A further result of mechanical properties shows that Ta enhances the strength of Co3(Al, Nb) while Ni deteriorates it. The disparate impact can be traceable from the electronic hybridization surrounding the nucleus of the solute atom.