THE LIQUID IMPACT RESISTANCE OF A RANGE OF IR-TRANSPARENT MATERIALS

The IR-transparent windows on high velocity aircraft have, to date, been fabricated from materials notable for their poor resistance to erosion. It is therefore essential that the effect on rain erosion resistance of applying protective coatings to these materials be accurately assessed. The Cavendish Laboratory multiple impact jet apparatus (MIJA) has produced accurate liquid impact data on a large number of materials and coating systems, the bulk of which are on IR window candidate materials. This study has revealed the care that must be taken to produce an optically acceptable coating system which will provide anything greater than a marginal improvement in rain erosion damage threshold velocity. MIJA has also been used to characterise chemically vapour-deposited diamond samples of different types and from various sources from which, it is hoped, the next generation of IR windows will be constructed, providing a component with high strength and high thermal shock and erosion resistance.