<title>Aluminum nitride coatings for protection of diamond at high-temperature in air</title>

Abstract

Diamond is an ultra-durable material with high thermal conductivity and good transmission in the visible, near IR and far IR wavebands. Advances in the performance of synthetic diamond made by chemical vapor deposition promise an expanding range of applications for the material. An example is in advanced airborne windows and domes for high- speed flight, either as a window or as a protective coating for other IR window materials. Diamond has sufficient durability to withstand high-speed impact by solid particles and raindrops and a high level of thermal conductivity to minimize the effect of thermal shock due to aerodynamic heating. However, diamond is subject to oxidation in air at temperatures greater than 750 degrees C. After only a few seconds exposure at such temperatures the diamond surface becomes severely etched, and the optical transmission is degraded. Very high-speed flight can lead to temperatures in excess of 800 degrees C. This means that, in high temperature applications, a coating is required which can protect the diamond surface from exposure to air. In addition the coating must have excellent adhesion and mechanical durability, and itself be resistant to impact. Using sputtered coatings based on aluminium nitride, we have demonstrated complete protection for extended exposures at temperatures up to 1000 degrees C. The coatings also have excellent mechanical durability as demonstrated by particle erosion test.