Multifunctional Silicon Aluminum Oxynitride (SiAlON) Ceramic Coatings for High Temperature Applications

摘要

This project has demonstrated how controlled synthesis of nanostructured SiAlON thin films with varying composition yields an outstanding class of wear resistant and oxidation resistant coatings. SiAlON thin films spanning the full range of O/N and Al/Si ratios were deposited by RF magnetron co-sputtering of Al and Si targets in Ar/O2/N2 mixtures onto bare sapphire and Pt coated sapphire substrates. The films are amorphous and very smooth when deposited at 200 degrees C and remain amorphous even after extended post- deposition annealing in vacuum, N2, or air up to 1500 degrees C. Nitrogen rich film compositions are extremely wear resistant when measured in sliding contact with steel or sapphire pins. The film stoichiometry remains unchanged at high temperature in vacuum or N2 but the films lose nitrogen during air annealing. A thin film interfacial oxidation sensor was developed and embedded at the SiAlON / substrate interface, and the oxygen penetration rate through the SiAlON film was inferred during isothermal annealing experiments at 1000 degrees C in air. Film exposure to O* and O2(+) species produced by an electron cyclotron resonance (ECR) source leads to rapid surface oxidation and corresponding nitrogen loss. Gradient film compositions offer the possibility of improved oxidation resistance.