Thermodynamics of the bainitic transformation in a CuZn alloy

Abstract

The driving forces for various possible reactions within the bainitic transformation temperature range of Cu 40 at.% Zn alloy have been calculated. The results show that because of the occurrence of β→β′ ordering transition within the temperature range, the driving forces ΔG^{β′→α′} and ΔG^{β′→β′+α} increase inversely with decreasing temperature, with ΔG^{β′→α′} > 0 and ΔG^{β′→β′+α} < 0. Moreover, the equilibrium temperature T₀ of the two phases β′ and α′ is far below the experimental B_s for alloys of various compositions. Therefore, the bainitic transformation in CuZn alloys can only proceed as that of diffusional reaction β′→β₁′+α.