SHAPE MEMORY PROPERTIES OF RAPIDLY SOLIDIFIED Ti50Ni50-XCuX (X=20, 25) ALLOY STRIPS

Abstract

The shape memory alloy strips of Ti50Ni30Cu20 and Ti50Ni25Cu25 have been fabricated by arc melt over flow technique. Their microstructures and shape memory characteristics were investigated by means of X-ray diffraction (XRD), optical microscopy and differential scanning calorimetry (DSC). The microstructure of the as-cast strips exhibited columnar grains normal to the strip surface. XRD analysis showed that the martensitic transformation of B2-B19 occurred in the alloy strips. During thermal cyclic deformation with the applied stress of 60 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be 4.9 degrees C and 1.8% in Ti50Ni30Cu20 alloy strip and 3.5 degrees C and 1.7% in Ti50Ni25Cu25 alloy strip. The as-cast strip of Ti50Ni25Cu25 alloy also showed a perfect superelasticity and its stress hysteresis was as small as 14 MPa. These mechanical properties and shape memory characteristics of the alloy strips were ascribed to B2-B19 transformation and the controlled microstructures produced by rapid solidification of the arc melt over flow process.