Shape memory alloys exhibit superelasticity and shape memory properties by virtue of a reversible phase transformation between austenite and martensite. Here, 14% recoverable strain is reported in a Heusler-type Ni52.87Mn23.82Ga23.32 microwire, fabricated by rapid solidification via the Taylor method, with a diameter of 110 µm. The microwire exhibits superelastic strain of ~11%, very low Young’s modulus of ~5.5 GPa, critical stress of ~110 MPa and mechanical stability during cyclic tensile test. We attribute this enhanced ductility and large superelasticity to the stress-induced martensitic phase transformation. The energy conversion and the structure of martensitic phase induced by stress are also discussed.
Abstract:The effects of initial oriented columnar grains on the texture evolution and magnetostriction in (Fe 83 Ga 17 ) 99.9 (NbC) 0.1 rolled sheets were investigated. The recrystallization texture evolution exhibited the heredity of initial orientations, concerning the formation of cube and Goss textures in the primary recrystallized sheet for the columnar-grained sample. Moreover, the growth advantage of Goss grains was more obvious than that of cube grains during the secondary recrystallization process. Because of the combined effect of this and Nb-rich precipitates as inhibitors, a sharp Goss texture and very large Goss grains were achieved in the secondary recrystallized sheet for the columnar-grained sample. For comparison, the secondary recrystallization in the equiaxed-grained sample was not fully developed although there were Nb-rich precipitates as inhibitors. We think this could be ascribed to the large particle size and premature coarsening of precipitates. Magnetostriction of the secondary recrystallized columnar-grained sheet was up to 232 ppm owing to the ideal Goss texture and quite large grain size. As for the equiaxed-grained sample, the magnetostriction was only 163 ppm in the secondary recrystallized sheet.
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