Additive manufacturing of functionally gradient refractory coatings using substrate dilution and in-situ carbide formation

Abstract

Enabling operations in extreme environments remains a top priority for the space, defense, and energy sectors, driving the demand for ultra-high-temperature materials. Traditional materials employed in these sectors have limited operating temperatures and thus novel alternatives are of interest. Refractory metals and carbides have excellent high-temperature properties, however, their high melting points and susceptibility to cracking during solidification make them challenging to process, especially through additive manufacturing (AM) technologies. In this work, Directed Energy Deposition (DED) was used to create a functionally graded refractory coating (W-WC-Nb system on a titanium substrate) by integrating titanium into the refractory matrix through substrate dilution. By developing a new W-based alloy then adding titanium from the substrate along the build direction, a crack-free microstructure was formed within layers closer to the substrate. Additionally, an in-situ carbide formation strategy was explored, creating titanium carbide and niobium carbide phases that could improve the high-temperature and corrosion properties without the need to overcome processing difficulties associated with these high-melting carbides. These strategies allow for the development of new material systems with tailored properties and improved processibility of refractory material systems.