BCC Refractory MPEAs for Laser Processing (and Additive Manufacturing)—From Computational Models to Additive Manufacturing

BCC refractory multi-principal element alloys (RMPEAs) exhibit significant potential for high-temperature structural applications (1000–2000 K) in fusion reactors, the space industry, and high-performance turbines. However, only a small fraction of their extensive and varied compositional design space has been explored, leaving many potentially valuable alloys undiscovered.<br/>This study investigates the design and manufacturing of RMPEAs for fabrication by beam-based additive manufacturing technologies, focusing on enhancing phase stability at high temperatures and refining grain structures without requiring extensive post-processing.<br/>The use of additive manufacturing (AM) techniques addresses challenges such as segregation and coarse grain formation during solidification, offering insights into RMPEA behaviour across various temperature regimes and cooling rates. Laser processing offers high cooling rates, which prevent the formation of highly segregated, dendritic structures commonly seen in arc melting or casting. It also shortens diffusion lengths, resulting in a more uniform chemical composition and smaller grains, thereby reducing the annealing time. Moreover, AM enables near-net zero-shape manufacturing, surpassing the potential problems of machining due to high hardness and material waste, which enhances sustainability.<br/>Employing CALPHAD-based alloy screening procedures (TC-Python) and computational models, promising candidates of 3-element alloys within the Hf-Mo-Nb-Ta-Ti-Zr master system with anticipated (?) properties are identified. Metastable phase transformations within RMPEAs are exploited through in situ X-ray diffraction at elevated temperatures (1273 K) and ex-situ heat treatment at 1623 K. To uncover the laser processing potential of the newly designed alloys, the arc-melted samples have been laser-treated to evaluate the potential for manufacturing crack-free parts. Arc-melted, heat-treated, and laser-processed bulks have been characterized by SEM, EDS, EBSD, XRD, and nanoindentation.<br/>Overall, this interdisciplinary approach combines computational modelling, alloy design strategies, and advanced manufacturing techniques to push the boundaries of RMPEAs. It contributes to the development of additive manufacturing technologies and paves the way for improved mechanical properties in extreme environments.