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

高温形状记忆合金(HT-SMA)的特点是相变温度高于100°C。设想的应用是在高温条件下具有成本和资源效益的致动器和传感器。Co-Ni-Ga是最有前景的高温超导材料之一，它的特点是成本相对较低，在500℃左右的温度下具有优异的功能性能，并且相变应力对温度的依赖性很小。然而，Co-Ni-Ga具有很难加工的性能，并且表现出与颗粒尺寸和织构有关的功能性质的强烈依赖性。在应用项目的范围内，应使用基于3D激光的直接能量沉积(DED)，以克服先前可加工性的限制，并定制微观结构，从而实现功能梯度结构。通过局部叠加超声波，不仅可以在几层上创建不同的微结构，而且可以在一层内创建不同的微结构，从而为三维梯度结构铺平道路。后处理热处理可提高合金的塑性和相变温度。特别是，通过在基体中引入析出物来实现较低的相变温度，而通过改变短程序来实现较高的相变温度。全面的微观结构和功能表征，特别是通过原位方法，将使人们能够对加工、微观结构和功能性能之间的关系有初步的了解。

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.