Crystal growth of Co46Ni27Ga27 ferromagnetic shape memory alloys with large single-variant set

The present work proposes a directional solidification method based on liquid melt cooling (LMC) technique to prepare large grain with single-variant set in Co–Ni–Ga alloys. The competitive growth from equaixed grains to steady columnar crystals with 1 1 0 orientation along the axis was observed. The directionally solidified rod has a uniform chemical composition. It can be also found that the unidirectional lamellar martensitic variants were well aligned in a whole grain, forming a single-variant state. Furthermore, the needle-like Ni₃Ga-type γ′ precipitates were formed in alloy with lower growth velocity, and it exhibited the complicated microstructural evolution. At the lowermost part of rod-like crystal, a large number of precipitates were dispersed both in grain interiors and at boundaries but its amount decreased when the columnar crystals were formed and gradually increased again from bottom up to top in the whole rod.