Effect of heat treatment time on microstructure and mechanical properties of Ti-19Nb-9Zr (at%) shape memory alloy

The effect of heat treatment time on microstructure and shape memory effect of Ti-19Nb-9Zr (at%) alloy is investigated. The transformation energy and constituent phase show tremendous sensitivity to the heat treatment time. In the present work, the HT10 (Heat-treated for 10 min) TiNbZr specimen consists of a large amount of martensites and obtained the highest martensitic transformation energy (similar to 11 J/g) while the HT80 (Heat-treated for 80 min) TiNbZr shows a predominant beta structure with very low martensitic transformation energy. Furthermore, athermal omega phase is found in the HT80 TiNbZr specimen. Since a longer heat treatment time followed by quenching (with larger grain size) is in favor of the formation of athermal to phase, we suggested that the fine athermal to phase may be attributed to the decrease of thermodynamic driving force of martensitic transformation. Filially, perfect shape memory effect is obtained after heating when the maximum pre-strains loading up to 6% in the precipitate free HT10 TiNbZr specimen. (C) 2012 Elsevier B.V. All rights reserved.