The strength of free-standing CVD diamond

Infra-red (IR) materials have an important role as protective “windows” to IR optical systems and sensors in high-speed flight. However, the transmission of an IR window can be seriously reduced by rain, dust, sand and ice impacts. Flaws and roughening produced by these impacts can affect both transmission and strength. The latter may ultimately lead to catastrophic failure. In this research, the strength of some IR materials, namely free-standing chemically vapour deposited (CVD) diamond, sapphire and zinc sulphide, were determined before and after solid particle erosion. The surface roughening caused by erosion is shown to be important with sapphire and zinc sulphide, because the flaws introduced are significantly larger than pre-existing intrinsic defects. However, the strength of CVD diamond is not affected by erosion, because the surface flaws introduced are less important than the intrinsic defects within the bulk. Despite the relatively large intrinsic flaws in CVD diamond it shown that the strength and erosion resistance are significantly higher than with other IR materials.