Microstructure evolution and magnetic properties in Mn-rich Ni-(Co, Cu, Fe)-Mn-Sn Heusler base shape memory alloys

Abstract

A prospective high temperature polycrystalline Ni50Mn44Sn6 Heusler shape memory alloy transforms at 637 K into 14 M and NM martensites with a14M = 6.278, b14M = 6.127, c14M = 5.654; and aNM = 5.449, cNM = 6.380 Å lattice parameters, theoretically yielding 9.9% (14 M) and 14.6% (NM) mechanically induced strain due to detwinning of martensite in single crystal. The substitution of Ni for Co, Cu and Fe (5 at.%) brings the martensitic transformation to lower temperatures (ΔT = 129 K), whereas the martensite develops into NM (Co) and 6 M (Fe & Cu) structures offering up to 13.9% theoretical strain (Co; NM). The Ni45Fe5Mn44Sn6 alloy is singled out by non-uniform composition; i.e. the γ phase coexists with 6 M martensite, and a ferromagnetic order setting in below 301 K, whereas all other alloys are chemically homogenous and predominantly paramagnetic. The results qualify the studied alloys as interesting candidates for high temperature shape memory alloys applications.