Microstructure and magnetic field induced strain of directionally solidified ferromagnetic shape memory CoNiAl alloys

This paper investigates the microstructure evolution in directionally solidified ferromagnetic shape memory Co37Ni34Al29 alloys by changing the solidification conditions and heat treatment process. From optical microscopy observations, the martensitic transformation temperature can be controlled by the composition of the matrix, and is especially dependent on the Al content. In addition, a preferred 〈1 1 0〉 orientation for the parent phase was obtained at the pulling rate of 25 μm/s and a relatively large 130 ppm strain in the single martensite polycrystalline CoNiAl was induced by an external magnetic field up to 7 kOe.