“Additive manufacturing of ultra-high temperature ceramics by digital light projection”

Matthew Thompson, MSE PhD Candidate 

Advisors: Professor Rod Trice and Dr. Gregory Scofield

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ABSTRACT

Ultra-high temperature ceramics (UHTCs) are promising materials for hypersonic vehicles due to the harsh aerothermal environment experienced during hypersonic flight. Additive manufacturing techniques, such as digital light projection (DLP), allow net shaping of ceramic components with the tight tolerances and fine feature sizes required for hypersonic applications. DLP printers cast a photosensitive slurry under a doctor blade, expose the slurry to UV light in the form of a 2D bright-dark contrast pattern, and build a ceramic part layer-by-layer from the bottom up by embedding ceramic particles in a cured polymer matrix. While advantages of DLP printing include low surface roughness, small feature size, and complex geometries, wider adoption of DLP technology is limited by poor printability of ultra-high temperature ceramics. In particular, a large difference in refractive index between the ceramic powder and the UV curable monomer causes low cure depths in DLP slurries. This critical review will analyze strategies in the open literature to improve the cure depth of ceramic-loaded suspensions consisting of silicon carbide, silicon nitride, and zirconium diboride by coating the surface of the powder with an oxide shell (a lower difference in refractive index would be expected to increase cure depth). At the same time, approaches to modify the surface chemistry of ceramic powders to control particle interactions in suspensions will also be discussed for the development of DLP slurries demonstrating a printable rheology. Knowledge gaps and opportunities for further investigation are presented to formulate well-dispersed suspensions of UHTCs and UV curable resins that are additively manufacturing through DLP to produce dense, high-performance sintered ceramic parts suitable for hypersonic applications.