Functionally graded Co-Ni-Ga high-temperature shape memory alloys manufactured via ultrasound assisted 3D laser-based directed energy deposition

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High-temperature shape-memory alloys (HT-SMAs) are characterized by transformation temperatures above 100 °C. Envisaged applications are cost- and resource-efficient actuators and sensors in a high temperature regime. One of the most promising HT-SMAs is Co-Ni-Ga, which is characterized by comparatively low costs, excellent functional properties up to temperatures of about 500°C and a low dependency of transformation stresses on temperature. However, Co-Ni-Ga possess a difficult workability and shows a strong dependency of functional properties with respect to grain size and texture. Within the scope of the applied project, 3D laser-based direct energy deposition (DED) should be used to overcome previous limitations of workability and to tailor microstructural and, thus, functionally graded structures. By locally superimposed ultrasonic waves, it will be feasible to create different microstructures not only over several layers but also within a single layer, thus paving the way for three-dimensionally graded structures. The ductility of the alloy as well as the transformation temperatures will be improved by post processing heat treatments. In particular, lower transformation temperatures will be realized by introducing precipitates into the matrix and higher transformation temperatures will be realized by changing the shortrange order. A comprehensive microstructural and functional characterization, in particular by means of in situ methods, will enable elementary insights in the relation between processing, microstructure and functional properties.