Enhanced Sinterability of Complex-Shaped 3D Printed Silicon Nitride

Multiple stereolithography 3D printer OEMs offer silicon nitride (SN) particulate loaded resins claiming to achieve full densification and mechanical properties approaching 80% of traditionally processed material.  However, repeatable printing of complex-shaped parts without warping and cracking is a significant challenge, which must be addressed in order for practical application of 3D printed silicon nitride for DoD applications such as conformal heat exchangers, microwave lenses, radomes, and propulsion components.  Technology Assessment and Transfer, Inc. proposes to build on its legacy of DLP 3D printing to demonstrate a photocurable resin loaded with at least 50 v% SN particulates, compared to the more typical 40 v% offered by foreign-based printer OEMs.  Higher solids loading has the clear benefit in producing green bodies with less organic content to burn out as well as higher green density to promote sintering.  TA&T will build on past demonstrations of DLP printable 50 v% solids resins with viscosity <10,000 cP, focusing on tailoring the particle size distribution, particle morphology, and matching appropriate dispersants and plasticizers for achieving desired print rheology.  Given the high refractive index and absorbance of SN compared to oxide technical ceramics such as Al2O3 at the UV wavelengths, curing behavior of a 50 v% SN resin will be limited.  Thermal oxidation of the SN particle surfaces will be used to reduce these effects.  The phase I effort will focus on SN-filled resin trials leading to printing and sintering demonstrations.  In phase II, the team will partner with US-based printer OEM 3D Fortify to scale printing operations and demonstrate a device, such as a high-temperature meta-structured radome.