Laser additive manufacturing is a technology that utilizes a laser beam to melt and mold powders layer by layer based on a 3D model. It has made outstanding progress in the molding of metallic structural materials such as large and complex structural parts in the aerospace industry. Laser additive manufacturing has also achieved remarkable progress in the fabrication of metallic functional materials. Shape memory alloys are a type of metallic functional materials that exhibit shape memory, superelasticity, and elastocaloric effects. Through design and optimization of the process strategy, shape memory alloys with excellent functional properties and complex shapes could be fabricated by laser additive manufacturing. Laser additive manufacturing offers an effective method to research metallic functional materials with outstanding performance that can meet the application requirements.

In this paper, we systematically summarize the research on laser additive manufacturing of metallic functional materials and their characterization by in-situ synchrotron radiation. We further introduce the research progress on laser additive manufacturing of high-performance shape memory alloys as well as the latest progress of metal L-PBF and L-DED technologies for synchrotron radiation-based in-situ X-ray diffraction (XRD) research. In the first part of this paper, the dominant types of laser additive manufacturing and their basic principles are introduced. On this basis, the relationship between the functional properties of shape memory alloys and the parameters of the process strategy is revealed. This relationship offers a guideline for how to fabricate a shape memory alloy with targeted properties. In the next part, the research progress on high-density shape memory alloys fabricated through laser additive manufacturing is introduced. The guidance of results predicted by computer is convenient for selecting the combinations of parameters that could be used to fabricate shape memory alloys with high density. The final part presents the research progress on synchrotron radiation-based in-situ X-ray characterization in the laser additive manufacturing process. This part introduces the characterization platform and typical applications of in-situ XRD in the laser additive manufacturing process of metallic materials. We describe some scenarios involving the phase transition dynamics measurement and in-situ characterization methods of single crystals in additive manufacturing. We also present the future development trends.

The molten pool in L-PBF and L-DED metal additive manufacturing processes has the characteristics of non-equilibrium and rapid solidification, and the microstructure of metallic functional materials can be controlled by adjusting the parameters of these processes. The additive manufacturing process may produce micro-defects such as keyholes and lack of melting, and it also tends to form columnar crystals with a certain orientation. Based on the Eager-Tsai model, a fabrication-quality distribution map can be predicted, with the parameters as the coordinates. On this basis, the process strategy can be adjusted to obtain a columnar crystal alloy with high orientation and high quality, and the mechanical properties can be further optimized. Synchrotron radiation-based in-situ XRD can effectively characterize the phase transition dynamics, texture evolution, and grain size changes in the additive manufacturing process, which provides insights into the control of the process parameters in additive manufacturing of metallic functional materials. The application of synchrotron radiation-based in-situ XRD can provide a key reference for additive manufacturing in terms of improving the functional characteristics and optimizing the component quality. By delving deeper into the microscopic evolution of the additive manufacturing process, researchers can better understand the properties of metallic materials, so that they can precisely manipulate the process parameters to achieve precise controlling of metal functional materials.