  Selective laser reaction sintering techniques (SLRS) techniques were
investigated for the production of near net-shape non-oxide ceramics including
SiC, Si$_3$N$_4$, and HfC/SiC composites that might be compatible with
prevailing powder bed fusion additive manufacturing processes. Reaction bonded
layers of covalent ceramics were produced using in-situ reactions that occur
during selective laser processing and layer formation. During SLRS, precursor
materials composed of metal and/or metal oxide powders were fashioned into
powder beds for conversion to non-oxide ceramic layers. Laser-processing was
used to initiate simultaneous chemical conversion and local interparticle
bonding of precursor particles in CH4 or NH3 gases. Several factors related to
the reaction synthesis process (precursor chemistry, gas-solid and gas-liquid
synthesis mechanisms, precursor vapor pressures) were investigated in relation
to resulting microstructures and non-oxide yields. Results indicated that the
volumetric changes which occurred during in-situ conversion of single component
precursors negatively impacted the surface layer microstructure. To circumvent
the internal stresses and cracking that accompanied the conversion of Si or Hf
(that expands upon conversion) or SiO$_x$ (that contracts during conversion),
optimized ratios of the precursor constituents were used to produce near
isovolumetric conversion to the product phase. The results demonstrate that
under appropriate processing conditions and precursor selection, the formation
of near net-shape SiC and SiC composites might be achieved through single-step
AM-compatible techniques.
