AVS 50th International Symposium
    Advanced Surface Engineering Tuesday Sessions
       Session SE-TuA

Paper SE-TuA1
Synthesis and High Temperature Performance of SiAlON Thin Film Coatings

Tuesday, November 4, 2003, 2:00 pm, Room 323

Session: High Temperature Protective Coatings
Presenter: R.J. Lad, University of Maine
Authors: J.I. Krassikoff, University of Maine
G.P. Bernhardt, University of Maine
M. Call, University of Maine
R.J. Lad, University of Maine
Correspondent: Click to Email
SiAlON ceramics made by alloying Al@sub 2@O@sub 3@ and Si@sub 3@N@sub 4@ possess oxidation resistance, high strength, and thermal shock resistance, which make them extremely attractive for high temperature coating applications. However, most work to date has emphasized bulk sintered SiAlONs rather than thin coatings. We have synthesized well-defined SiAlON thin films using rf magnetron sputtering of Al and Si targets in Ar / O@sub 2@ / N@sub 2@ mixtures on sapphire substrates. By manipulating the relative amounts of the deposition fluxes, homogenous versus multilayer or gradient SiAlON structures with a range of stoichiometries were produced. The films remain amorphous even with post-deposition annealing in vacuum or air up to 1000°C. Moreover, the film stoichiometries remain stable at high temperature in vacuum but lose nitrogen during air annealing. A thin film Ni-Cr corrosion sensor was embedded at the SiAlON / substrate interface, and the rate of oxygen penetration through the SiAlON film structures was measured in situ during accelerated thermal cycling tests in 1000°C oxidative environments. The time to failure ranges from hours to weeks depending on the exact SiAlON composition. Multilayer films with an Al@sub 2@O@sub 3@ overlayer exhibit the best oxidation resistance. Pin-on-disk wear tests indicate that the wear rate is also a function of the SiAlON stoichiometry. Our results yield important information that can be used to design and fabricate multifunctional SiAlON environmental barrier and thermal barrier coatings.@footnote 1@ @FootnoteText@@footnote 1@ Supported by AFOSR Grant #F49620-02-1-0323.