The solid particle erosion of free-standing CVD diamond

Modern aircraft employ sophisticated electro-optic sensors. It is essential to protect these sensitive optical systems from relatively high-speed impacts with airborne dust particles. A loss in transmission caused by such an event can impair guidance, and catastrophic failure may occur. Protection is afforded by the installation of a hard cover that is transparent in the relevant regime. Diamond is potentially by far the most attractive window material due to the excellent optical and mechanical properties, but is expensive and difficult to shape. Chemical vapour deposited (CVD) diamond is a polycrystalline synthetic with properties that approach those of single crystal diamond, and it can be more easily shaped. The aims of the present research were to quantify the erosion and transmission losses of CVD diamond, and to understand the material removal mechanisms involved. Steady-state erosion rates were obtained for CVD diamond of different grain sizes, using 300–600 μm quartz erodent at velocities between 60 and 140 m s−1. Images of CVD diamond at various stages of erosion, obtained using an optical microscope and an environmental scanning electron microscope (ESEM), reveal that erosion initially occurs at grain boundaries and that so-called “micro-features” also have some influence on erosion.