Bending strength increase of silicon carbide by density gradient structure design by direct ink writing

In this study, density-gradient silicon carbide (SiC) was fabricated using direct ink writing with alumina and yttria as sintering additives. The structure in which a high-density layer is sandwiched between low-density layers exhibited a 48% increase in bending strength compared to a monolithic high-density structure. High-speed camera imaging revealed that cracks in all bending tests consistently initiated on the bottom surface of the specimen, where tensile stress is applied. In the structure in which a high-density layer is sandwiched between low-density layers, the compressive stress in the low-density layer suppressed crack initiation, and the residual stress was highest at the interface between high- and low-density layers. This design concept suggests that using a relatively low-density structure on the SiC surface, where cracks are likely to initiate, and minimizing the distance from the SiC surface to the interface between high- and low-density layers can enhance crack initiation suppression and improve bending strength.