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Effect Of Crystal Quality On Twinning Stress In Ni–Mn–Ga Magnetic Shape Memory Alloys, Andrew Armstrong, Peter Müllner

Materials Science and Engineering Faculty Publications and Presentations

Low twinning stress (TS) is a prerequisite for magnetic shape memory functionality in ferromagnetic martensites. We compare Ni₅₀Mn₂₈Ga₂₂ (nominal at.%) single crystals from four different producers to reveal the effect of crystal quality on the TS. Near the reverse martensite transformation, the TS is generally low, about 1 MPa, regardless of mosaicity of up to 1.7° and chemical composition deviations of up to 2 at.% of Mn. Pure type I and type II twin boundaries occur in crystals with smooth chemical composition gradients. The corresponding temperature dependences of TS follow universal linear trends with the …