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Microstructural origins of martensite stabilization in Ni49Co1Mn37.5Sn6.5In6 metamagnetic shape memory alloy

Czaja, P., Przewoźnik, J., Kowalczyk, M., Wierzbicka-Miernik, A., Morgiel, J., Maziarz, W.
Journal of materials science 2019 v.54 no.5 pp. 4340-4353
Gibbs free energy, alloys, annealing, cooling, heat treatment, magnetism, temperature
Ordering effects in the Ni₄₉Co₁Mn₃₇.₅Sn₆.₅In₆ alloy were studied by subjecting the alloy to annealing at 1220 K followed by water quenching and to subsequent annealing at 1070 K followed by slow cooling. Martensitic transformation temperature increases by 10 K owing to the slow cooling process, which further invites a change in the martensite structure: 6M → 10M. Across the transformation, regardless of the heat treatment applied, austenite phase is paramagnetic and it transforms into a weakly magnetic martensite. Magnetic moment of martensite is boosted due to slow cooling ([Formula: see text]). Observed behaviours are associated with the changes in the degree of atomic ordering. Irrespective of the magnetic state of martensite, ordering process mitigates the transformation temperature most likely through the interaction with the free energy difference and through the influence of antiphase domains on the twinning stress.