Oxidation of metastable single‐phase polycrystalline Ti0.5Al0.5N films: Kinetics and mechanisms
作者:
D. McIntyre,
J. E. Greene,
G. Ha˚kansson,
J.‐E. Sundgren,
W.‐D. Mu¨nz,
期刊:
Journal of Applied Physics
(AIP Available online 1990)
卷期:
Volume 67,
issue 3
页码: 1542-1553
ISSN:0021-8979
年代: 1990
DOI:10.1063/1.345664
出版商: AIP
数据来源: AIP
摘要:
Metastable single‐phase, NaCl‐structure, polycrystalline Ti0.5Al0.5N alloy films have been shown to exhibit much better high‐temperature (750–900 °C) oxidation resistance than polycrystalline TiN films grown under similar conditions. The Ti0.5Al0.5N alloys, &bartil;3 &mgr;m thick, were deposited at temperatures between 400 and 500 °C on stainless‐steel substrates by dc magnetron sputter deposition in mixed Ar+N2discharges with an applied negative substrate biasVsof either 0 or 150 V. Oxidation in pure O2initially occurred at a rate that varied parabolically with time. The oxide overlayers consisted of two partially crystalline sublayers, the upper one Al‐rich and the lower one Ti‐rich, with no measurable N concentrations in either. Inert‐marker transport experiments showed that oxidation proceeded by the simultaneous outward diffusion of Al to the oxide/vapor interface and inward diffusion of O to the oxide/nitride interface. The oxidation rate constant K increased with oxidation temperatureToxat a rate much higher than would be predicted from a simple exponential dependence due to changes in the oxide microstructure (increased crystallinity) with increasingTox. AtTox≥850 °C, O transport became the rate‐limiting step. After oxidation times, ranging from 6 h at 750 °C to 7 min at 900 °C, oxide crystallites, exhibiting a tetragonal rutile TiO2structure, were observed inVs=0 samples to grow at an accelerated rate up through cracks in the oxide overlayer. The formation of these crystallites was postponed until a much later stage in oxide‐overlayer development for samples grown withVs=150 V.
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