DEPOSITION AND ANALYSIS OF IR-AL COATINGS FOR OXIDATION PROTECTION OF CARBON MATERIALS AT HIGH-TEMPERATURES

The use of Ir-Al coatings to protect carbon materials from oxidation in high-temperature environments has been investigated. A coating process was developed using a three-gun magnetron sputtering system with a single focal-point geometry to deposit Ir-Al coatings up to 5 μm in thickness. By elevating the substrate temperature, uniform, non-porous coatings were achieved on graphite and sapphire substrates. The stability of two Ir-Al phases (IrAl3 and IrAl) in vacuum was studied as a function of annealing temperature. Both phases were found to decompose in vacuum via aluminum vaporization: IrAl3 was converted completely to IrAl at 1200 °C, and IrAl converted completely to iridium at 1400 °C. Evidence of these decompositions was observed using several analytical techniques: Auger electron spectroscopy, energy dispersive spectroscopy, scanning electron microscopy and X-ray diffraction. © 1989.