Martensitic transformation behaviors of Ti49+xNi21-xCu30 (x=0, 1, 2, 3) shape memory alloy strips

Abstract

Four batches of Ti-Ni-Cu strips (Ti49Ni21Cu30, Ti50Ni20Cu30, Ti51Ni19Cu30 and Ti52Ni18Cu30) were prepared by an arc melt overflow technique. The microstructure of as-cast strips exhibited columnar grains normal to the strip surface. XRD analysis showed that B2-B19 martensitic transformation occurred in all alloy strips. The martensitic transformation start temperature (M-s) of the Ti49Ni21Cu30 strip was 54.6 degrees C and continued to increase with increasing Ti-content. During cycle deformation with an applied stress of 120 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be 4.1 degrees C and 1.84% in the Ti49Ni21Cu30 strip. The transformation hysteresis associated with the B2-B19 transformation increased with increasing Ti-content, while the elongation decreased with increasing Ti-content. Even though it is known that Ti-Ni-Cu alloys with high Cu-content (more than 13 at% Cu) are too brittle to deform plastically, the rapidly solidified Ti-Ni-Cu alloy strips, which contain 30 at% Cu, have excellent shape memory characteristics and mechanical properties.