Highly mobile twin boundaries in seven-layer modulated Ni–Mn–Ga–Fe martensite

Abstract

We report on low twinning stress of 0.2 MPa for type 1 twin boundaries with rational (101) twinning plane and 0.1 MPa for type 2 twin boundaries with rational [1¯01] twinning direction, in Ni2MnGa0.8Fe0.2 seven-layer modulated martensite exhibiting about 12% stress-induced strain. The studied samples were free of compound twins with (100) and (110) twinning planes. The martensite lattice is monoclinic and shows a long-period commensurate modulation with wave vector q=(2/7)g110, where g110 is the reciprocal lattice vector. The investigated alloy has high potential for practical applications due to the low twinning stress and the elevated Curie point TC=400 K.