Phase transformation behaviours of Ti-Ni-Cu shape memory alloy powders fabricated by mechanical alloying

In our research, Ti-Ni and Ti-Ni-Cu alloy powders were fabricated by mechanical alloying, and then phase transformation behaviours were investigated by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and transmission electron microscopy. The size of the Ti-Ni-Cu alloy powders decreased as Cu-content increased. The powders of as-milled Ti-Ni and Ti-Ni-Cu alloys with Cu-contents less than 5at.% were amorphous, whereas those of as-milled Ti-Ni-Cu alloys with Cu-content more than 10at.% were crystalline. These characteristics indicate that Cu addition tends to suppress amorphization of Ti-Ni based alloy powders. The monoclinic B19' martensite is formed in the Ti-Ni-Cu alloy powders with Cu-content less than 10 at.%, whereas the orthorhombic B19 martensite is formed in the Yi-Ni-Cu alloy powders Cu-content more than 10 at.%. The Fe contamination is reduced by decreasing rotation speed from 350 rpm to 250 rpm.