The shear modulus at room temperature of191 GPa for CVD SiC has been determined by the four-point bend­ing technique. This value was also derived from the elastic modulus and Poisson’s ratio (n), using the con­ventional formula for isotropic solids: G = E/2(1 + n). The temperature dependence ofshear modulus can be estimated from E by applying this formula.

2.12.2.1.3 Hardness23

There appears to be no significant difference between Vicker’s and Knoop hardness: H~ 20.7-24.5 GPa has been reported for CVD p-SiC. By contrast, slightly higher values were obtained by nanoindentation. Nanoindentation is known to yield local values which depend on microstructural features. The afore­mentioned exponential function ofporosity for elastic modulus can be extended to the hardness evaluation:

Hv = 27.7exp(-5.4Vp) [3]

where HV is the Vicker hardness.

Currently, there is no high-temperature data reported for high-purity CVD SiC.