A novel approach to fabricate Si3N4 by selective laser melting

Difficulties in sintering refractory ceramics limit their potential high-demanding applications. Selective laser sintering/melting of ceramics is extremely challenging due to poor sinterability of refractories caused by a low thermal shock resistance and an insufficient electron conductivity blocking absorption of laser electron beam energy, etc. Here, we propose a new approach to fabricate Si3N4-based complex geometry parts by selective laser sintering. This is a two-step approach including (i) selective laser sintering of silicon powder providing a needed shape, and (ii) nitridation of the as-shaped silicon parts aimed at fabrication of the Si3N4 component. Parametric study of the process has been performed for optimization of the sintering parameters, such as laser current, point distance and exposure time. The silicon component of full Archimedes density, 12 GPa Vickers hardness and 432 MPa compressive strength has been produced by SLS technique. Effect of different catalysts (Ni-, Cr-, Co-based) on the nitridation of the shaped silicon parts has been thoroughly studied. The conversion degree of nitridation reaches 50% with Ni-based catalyst subjecting growth of Si3N4 nanofibers on the surface of the component.