Effect of annealing conditions on microstructures and shape memory characteristics of Ti-50-Ni-30-Cu-20 alloy ribbons

Abstract

Ti-50-Ni-30-Cu-20 alloy ribbons without any crystal phases have been fabricated at the wheel velocities of 55 m/s and the melt spinning temperature of 1500 degrees C by melt spinning process. Their microstructures and shape memory characteristics were investigated by means of optical microscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The crystallization temperature was measured to be 440 degrees C. The crystallized ribbon exhibited fine microstructure after annealed at 440 degrees C for 10 min and was deformed up to about 6.8%. During thermal cycle with the applied stress of 220MPa, transformation hysteresis and elongation associated with a B2-B19 transformation were observed to be 4 and 3.6%. The ribbons showed a perfect superelasticity and their stress hysteresis was as small as 20 MPa which was attributed to the single pair martensite variants in small grains. This controlled microstructure was achieved by a proper heat treatment of amorphous ribbons in Ti-50-Ni-30-Cu-20 alloy. (c) 2006 Elsevier B.V. All rights reserved.