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）的特点是转变温度高于100℃。设想的应用是在高温状态下的成本和资源效率高的执行器和传感器。其中最有前途的ht - sma是Co-Ni-Ga，其特点是成本相对较低，在500°C左右的温度下具有优异的功能特性，并且转变应力对温度的依赖性较低。然而，Co-Ni-Ga具有难以加工的特性，并且在晶粒尺寸和织构方面表现出很强的功能特性依赖性。在应用项目的范围内，应该使用3D激光直接能量沉积（DED）来克服以前的可加工性限制，并定制微结构，从而实现功能梯度结构。通过局部叠加超声波，不仅可以在多层上，而且可以在单层内创建不同的微结构，从而为三维梯度结构铺平道路。通过后处理热处理，可以提高合金的塑性和相变温度。其中，通过在基体中引入析出相可以实现较低的转变温度，通过改变短阶可以实现较高的转变温度。全面的微观结构和功能表征，特别是通过原位方法，将使人们对加工、微观结构和功能特性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.