School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130, China...

The martensitic transformation for Co¬50Ni¬20Ga¬30 ribbon synthesized by the melt-spinning technique was studied by means of X-ray diffraction and ac magnetic susceptibility. The Co¬50Ni¬20Ga¬30 ribbon, having bcc phase with calculated lattice parameters of a=0.57431 nm at 313 K. It exhibits a structure transition from parent phase to martensite during cooling. The martensitic phase in Co¬50Ni¬20Ga¬30 ribbon is tetragonal structure with lattice parameters of a=b=0.5422 nm and c=0.6401 nm. (c/a>1). According to the changing of diffraction intensity for martensite and the change of ac magnetic susceptibility, the process of the martensitic transformation can be divided into three parts during cooling from 283 K to 213 K. When the temperature decreasing sequentially from 193 K to 110 K, the structure of the martensite has a change in which the a-axis decreases and c-axis increases. The morphologies of self-accommodation were observeds. The parallelogram morphology, the diamond morphology and the fork morphology were found.