Additive manufacturing of refractory metals and carbides for extreme environments: an overview

Refractory metals and their carbides possess extraordinary properties when subjected to high temperatures and extreme environments. Consequently, they can act as key material systems for advancing many sectors, including space, energy and defence. However, it has been difficult to process these materials using the conventional routes of manufacturing. Additive manufacturing (AM) has shown a lot of potential to overcome the challenges and develop new material systems with tailored properties. This review provides a fundamental understanding of the challenges in the processing of refractory metals and their carbides, including microcracking, formation of brittle oxide phases and high ductile to brittle transition temperature (DBTT). We also highlight some of the novel approaches that have been taken to improve the processability of these challenging material systems using AM. These include in-situ reactive printing, ultrasonic vibration, laser beam shaping, multi-laser deposition and substrate pre-heating with a focus on microstructural changes to improve the properties of printed parts.