Two L1.0 Phases Formation in Mn–Al–Ga Alloy with Different Ga Content

Abstract

Ga-doped Mn–Al alloys with compositions of Mn_58.5Al_31.8Ga_9.7 and Mn_58.3Al₃₄Ga_7.7 were produced by arc melting and subsequently successfully transformed into the ferromagnetic L1.0 phase. The pathways of complete transformations differed for the two alloys. For the 7.7 at % Ga alloy, a single-step cooling process at an intermediate rate was sufficient to transform it into the L1.0 phase. In contrast, the 9.7 at % Ga alloy required an additional annealing step at 550°C for 2 h to complete the transformation to the desired L1.0 structure. In second case the L1.0 phase consists of two distinct ferromagnetic L1.0 components with Curie temperatures of T_c1 = 302°C and T_c2 = 362°C, which evolved from different initial ε and γ₂ phases that were stable at 1100°C. The transformation of the γ₂ → τ phase was studied using electron back-scatter diffraction (EBSD), revealing that the τ(γ₂) phase began transforming from the interface and inherited the orientation of the τ(ε) phase at the interface, while the chemical compositions of both phases remained almost constant.