Boron Phosphide satisfies many of the material requirements for a coating suitable for use on high velocity IR windows. Such coatings have to be robust, resistant to abrasion and to rain erosion, and also capable of surviving thermal shock. Films of BP of several tens of microns in thickness have been produced by plasma assisted chemical vapour deposition on a variety of feedstocks. Growth has been achieved on a wide range of substrate materials, with no apparent limitation in film thickness, suggesting low levels of stress. The degree of optical transparency is high, covering 0.8 μm to 12 μm and beyond, with absorption levels being an order of magnitude lower than found for typical diamond-like carbon (DLC) films. The ability to survive severe erosive conditions is also significantly improved compared with DLC in wiper tests, water jet impact experiments are in whirling arm rain erosion tests.
|