Effects of Postdeposition Treatments on the Mechanical Properties of a Chemical‐Vapor‐Deposited Silicon Carbide

The influence of different postdeposition treatments such as water quench and thermal heating in air, nitrogen, and vacuum on mechanical properties of chemical‐vapor‐deposited (CVD) silicon carbide was investigated. The results showed that these postdeposition treatments increased the flexural strength by as much as 60% but did not significantly change other properties such as hardness and fracture toughness. The strength increase was achieved by treatments performed in both the oxidizing and nonoxidizing environments. Compressive residual stresses in CVD SiC increased because of these treatments, but this increase was not large enough to explain fully the observed increase in the flexural strength. It is proposed that these thermal treatments led to strength increase via healing of surface machining flaws. Thermal treatments in nonoxodizing environments reduced or blunted the flaws through the rearrangement of atoms and restoration of damaged crystal structure in SiC, while in oxidizing environments, passive oxidation may have served as an additional flaw healing mechanism.