A novel route for growing single-crystal and internal-stress-induced martensitic transformation of ferromagnetic shape memory alloys Co50Ni20Ga30

As a new single-crystal preparation method, undercooling directional solidification has been proposed for the case of the ferromagnetic shape memory Co50Ni20Ga30 rod. The as-grown single crystal has strong [1 1 1] orientation and a very homogenous composition along the rod axis, which confirms that the undercooling directional solidification is a feasible and effective approach for preparing Co–Ni–Ga single crystals. Additionally, the drastically increased transformation temperatures upon undercooling was ascribed to the internal stress induced martensitic transformation.

► Undercooling directional solidification is proposed as a new preparation method of single crystals. ► The microstructure and composition of the Co50Ni20Ga30 rod exhibit a perfect single crystal. ► The rod exhibits strong [1 1 1] preferred orientation. ► The martensitic transformation is induced by large internal stresses.