Advanced thermal stability investigations of the Mn-Al-Ga system

Abstract A ternary Mn-Al-Ga alloy with the nominal composition Mn 55 Al 38.57 Ga 6.43 was produced by arc melting. After homogenisation, the alloy consisted of the e and γ 2 phases. Appropriate heat treatments were used to transform each of these into a phase with the L1 0 structure. These two L1 0 phases had different compositions, lattice parameters and magnetic properties. In order to test the stability of the L1 0 phases against decomposition, heat treatments were carried out at 700 °C for durations of up to 14 days. The results showed that the decomposition started with formation of the β-Mn phase and subsequent appearance of the γ 2 phase. The resulting diffusion gradients resulted in composition changes in the L1 0 phases and after 7 days, only a single, intermediate composition remained. After 14 days, the decomposition was almost complete. The decomposition of the L1 0 phases in the ternary Mn-Al-Ga alloy was significantly slower than in binary Mn-Al alloys.