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

Ga-doped Mn–Al alloys with compositions of Mn58.5Al31.8Ga9.7 and Mn58.3Al34Ga7.7 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 Tc1 = 302°C and Tc2 = 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.