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Krooß, P.; Lauhoff, C.; Langenkämper, D.; Paulsen, A.; Reul, A.; Degener, S.; Aminforoughi, B.; Frenzel, J.; Somsen, C.; Schmahl, Wolfgang W.; Eggeler, G.; Maier, H. J.; Niendorf, T. (March 2019): Impact of Heating-Cooling Rates on the Functional Properties of Ti-20Ta-5Al High-Temperature Shape Memory Alloys. In: Shape Memory and Superelasticity, Vol. 5, No. 1: pp. 95-105
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Abstract

Due to their ability to provide a shape memory effect at elevated temperatures, high-temperature shape memory alloys (HT-SMAs) came into focus of academia and industry in the last decades. Ternary and quaternary Ni-Ti-based HT-SMAs have been in focus of a large number of studies so far. Ti-Ta HT-SMAs feature attractive shape memory properties along with significantly higher ductility and lower costs for alloying elements compared to conventional Ni-Ti-based HT-SMAs, which qualifies them as promising candidate alloys for high-temperature applications. Unfortunately, precipitation of undesired phases, e.g., the -phase, leads to significant functional degradation upon cyclic loading in binary Ti-Ta. Therefore, additions of ternary elements, such as Al, which suppress the -phase formation, are important. In the present study, the influence of different heating-cooling rates on the cyclic functional properties of a Ti-20Ta-5Al HT-SMA is investigated. Transmission electron microscopy as well as in situ synchrotron analysis revealed unexpected degradation mechanisms in the novel alloy studied. Elementary microstructural mechanisms leading to a degradation of the functional properties were identified, and the ramifications with respect to application of Ti-Ta-Al HT-SMAs are discussed.