Thermoelastic martensitic transformations in ternary Ni₅₀Mn_50–z Ga _z alloys

Abstract

We have studied the effect of gallium alloying on the structure, phase composition, and physical properties of ternary alloys of the Ni₅₀Mn_50–z Ga _z (0 ≤ z ≤ 25 at %) quasi-binary section in a broad temperature range. Dependences of the type of crystalline structure of the high-temperature austenite phase and martensite, as well as the critical temperatures of martensitic transformations on the alloy composition, are determined. A phase diagram of the structural and magnetic transformations is constructed. Concentration boundaries of the existence of tetragonal L1₀ (2M) martensite and martensitic phases (10M and 14M) with complex multilayer crystalline lattices are found. It is established that the predominant martensite morphology is determined by the hierarchy of packets of thin coherent nano- and submicrocrystalline plates with habit planes close to {011} _B2, pairwise twinned along one of 24 equivalent {011}<011> _B2 twinning shear systems.