Multicomponent Metallic Ni–Mn-Based Alloys with Thermally, Mechanically, and Magnetically Controlled Shape Memory Effects

Resumo

This paper presents the results of a systematic study of structural and magnetic phase transformations and properties of Ni–Mn-based alloys of the main four quasi-binary NiMn–NiTi, NiMn–NiAl, NiMn–NiGa and Ni₂MnGa–Ni₃Ga systems. Generalized phase diagrams of existing structural and magnetic phase transformations have been constructed. This study found that alloying with a third component (Ti, Al, Ga, and Mn) decreases the critical temperatures of thermoelastic martensitic transformations with respect to the critical temperatures of parent intermetallics. The morphology of martensite was shown in the hierarchy of packets of thin coherent nano- and submicron-sized crystals with inrterphase boundaries close to {011}_B2; the martensite crystals are twinned along one of the 24 {001}〈01\(\bar {1}\)〉 “soft” twinning shear systems in the austenite. This mechanism provides the coherent accommodation of thermoelastic martensitic transformation-induced elastic stresses.