Abstract
Titanium–tantalum shape memory alloys (SMAs) are promising candidates for actuator applications at elevated temperatures. They may even succeed in substituting ternary nickel–titanium high temperature SMAs, which are either extremely expensive or difficult to form. However, titanium–tantalum alloys show rapid functional and structural degradation under cyclic thermo-mechanical loading. The current work reveals that degradation is not only governed by the evolution of the ω-phase. Dislocation processes and chemical decomposition of the matrix at grain boundaries also play a major role.
Highlights
Titanium–tantalum shape memory alloys (SMAs) are promising candidates for actuator applications at elevated temperatures. They may even succeed in substituting ternary nickel–titanium high temperature SMAs, which are either extremely expensive or difficult to form
Buenconsejo and co-workers showed that binary Ti–Ta alloys are prone to rapid degradation due to the evolution of the !-phase and a concomitant stabilization of the β-parent phase.[8,10,11]
Transmission electron microscopy (TEM) using a FEI Tecnai F20 operating at 200 kV was employed to study the microstructural evolution in thin foils prepared from the gauge section of the samples
Summary
Titanium–tantalum shape memory alloys (SMAs) are promising candidates for actuator applications at elevated temperatures. Procedure like employing a higher number of cycles at higher temperatures or long-term creep testing can lead to severe functional degradation.[12,13,19] In case of cyclic thermo-mechanical loading, the rate of degradation was strongly reduced by Al additions, but qualitatively a similar degradation behavior was found.[13] In addition, it was shown that transformation strain capability can be restored by short-time annealing treatments.[12,13] the microstructural evolution in Ti–Ta–X alloys associated with thermo-mechanical cycling and thermal recovery treatments was not addressed.
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