Abstract
Abstract The transformation behavior of Ni50.5Mn30.4Ga19.1 and Ni53.7Mn26.4Ga19.9 was studied with ac magnetic susceptibility, differential scanning calorimetry, in-situ optical microscopy and X-ray diffractometry. The liquidus, solidus and L21⟶B2’ temperatures were detected for the alloys. The transformation enthalpies of melting, solidification and martensitic/reverse reactions were determined. In Ni53.7Mn26.4Ga19.9 the magnetic transition was clearly below the parent to martensite phase transformation and did not have hysteresis. The transformation sequence is suggested as Pparam ⟶Tparam ⟶ Tferrom with reverse reactions in respective order. In Ni50.5Mn30.4Ga19.1 the temperatures of the magnetic transition and structural phase transformations are close to each other and the Curie temperature shows a hysteresis of 9 K during cooling-heating cycle. Based on the combined measurements, the transformation sequences are assumed to be during cooling Pparam ⟶ 7Mparam ⟶ 7Mferrom ⟶ Tferrom and Tferrom ⟶ Tparam ⟶ 7Mparam ⟶ Pparam during heating. Consequently, the hysteresis in the magnetic transition is explained with the intermartensitic reaction and the difference of the Curie points of 7M and T phases.
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