Co-Printing of SiC Components Using Vibration Assisted Printing and Fused Filament Fabrication

Additive manufacturing (AM) of ceramics provides unique opportunities for volumetric control of part geometries and material gradients. Aerospace applications can benefit from these approaches that can combine high-temperature resistance with enhanced thermal diffusivity and low weight. Current AM methods for ceramics produce precursors that undergo significant shrinkage during the sintering stage and suffer from design limitations on feature sizes to minimize warping. The mixtures of ceramic powders with preceramic polymers are viable candidates for minimizing these effects to produce net-shape high-density parts, as the particles are already in contact at &gt;55 vol.% packing that resists shrinkage. However, the high solids loaded mixtures are extremely viscous due to particle contact points, making it challenging to use them in direct-write (DW) and stereolithography techniques.<br/>Vibration assisted printing (VAP) is a new DW AM method that has been demonstrated to process highly viscous high solids loaded mixtures such as polymer clays and solid propellants at rapid print rates (&gt;100 mm/s) and sub-mm resolution. In this work, VAP has been used to 3D print parts with mixtures of 84 wt.% (62 vol.%) silicon carbide (SiC) crystalline powder with a commercial polycarbosilane that forms SiC upon pyrolysis. The extruded mixtures exhibited creep that caused slumping as the parts were printed beyond a height of 3 mm. To alleviate this effect, a fused filament fabrication (FFF) print head was used concurrently with the VAP nozzle to print the outer walls using PLA and water-soluble PVA filaments that provided support. An initial infill was produced using a polymer clay to determine optimum settings followed by the SiC mixtures for subsequent prints. The ceramic parts were then cured at 523 K and pyrolyzed at 1573 K after removal of the thermoplastic components. The processed parts did not show any shrinkage and retained their original shapes with approximate porosities of 25 vol.% due to the mass loss and density change in the preceramic polymer.