Fracture strength of hot-pressed silicon carbide at the microscale

Tensile strength is a critical design parameter to ensure reliability of silicon carbide devices. However, SiC's tensile strength depends on the dominant flaw subjected to maximum tensile stress. Typically, processing related flaws (i.e. voids or inclusions) dominate the tensile response thereby masking role of the underlying microstructure. To probe the intrinsic microstructural flaws in a hot-pressed SiC microscale tensile bars were machined using a custom femtosecond laser micromachining apparatus from thin sections. When tested in tension, the fracture strength was dramatically higher compared to bulk tensile strengths. An analysis of strength-size scaling suggested a transition in the dominant strength-determining flaw at the microscale. Analysis of fracture surfaces and critical flaw sizes suggest failure is governed by isolated large grains. These observations have important implications for parameterizing ceramic failure models.