Processing and Functional Stability of Ti-Ta-based High Temperature Shape Memory Spring Actuators

Ti-Ta shape memory alloys (SMAs) are attractive for applications as high temperature SMAs due to their high M_S temperatures and excellent workability. We provide results on processing and fabrication of spring actuators. We show how high quality Ti-Ta alloys can be produced through arc melting and subsequent thermal and thermomechanical treatments. A processing route involving rotary swaging, wire drawing and thermal treatments was developed. Although the workability of Ti-Ta is relatively good, the production of thin wires is not trivial. Most importantly, the oxidation-related formation of brittle α-Ti layers in surface regions promotes the formation of a high density of cracks. Therefore, thermal exposure during processing needs to be minimized. We present a processing route which yields wires with defined microstructures. We also provide results on cyclic functional testing of Ti-Ta spring actuators using a new high temperature SMA test system where the effects of different thermomechanical parameters were identified.