Effect of precipitation on the shape memory effect of Ti50M25Cu25 melt-spun ribbon

The present research aims to provide accurate understanding of the relation between precipitation (volume fraction, morphology, type) and shape memory effect of Ti50Ni25Cu25 melt-spun ribbon. Rapid thermal annealing was used to control the micro structural development while the shape memory effect of the ribbon was determined under constraint thermal cycling. The results show that the precipitation process takes the following sequence: B11 TiCu -> B11 TiCu + Ti-2(Ni, Cu) -> Ti-2(Ni, Cu) with increasing annealing temperature or duration. The shape memory effect is found to depend on both the volume fraction and the distribution of the precipitates. The former affects the shape recovery strain through reduction of the transformation volume participating the shape recovery. The latter affects the shape recovery strain through strengthening the matrix thus reducing the martensite strain which is more predominant under low constraint stresses. Precipitation strengthening, on the other hand, reduces the tendency of dislocation generation/movement, thus reducing the irreversible strain and improving shape recovery strain. This understanding provides guidelines on the optimization of the shape memory properties of the Ti50Ni25Cu25 melt-spun ribbon via post-processing annealing. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.