Thermal stabililty and oxidation resistance of TiAlN/CrN multilayer coatings

• Published in: Surface & coatings technology Vol. 94-95; no. 1-3; pp. 315 - 321
• Main Authors: Wadsworth, I, Smith, I J, Donohue, L A, Munz, W-D
• Format: Journal Article
• Language: English
• Published: 21-04-1997
• ISSN: 0257-8972

TiAlN/CrN multilayer films with superlattice characteristics were deposited onto M2 high-speed steel and 304 stainless steel by reactive unbalanced magnetron sputtering involving three TiAl targets and one Cr target. The wavelength of the multilayer structures (ranging from 2.4 nm to 4.8 nm) and Cr content (from 10% to 30%) was controlled by varying the power supplied to the Cr target (P sub Cr ) from 2 kW to 12 kW. These coatings were then heated in an ambient atmosphere at temperatures ranging from 500 to 1000 deg C and for times up to 16 h. Breakdown of the multilayer structure was studied using such techniques as hardness measurements, x-ray diffraction (XRD) and cross-sectional TEM (XTEM). The results show that both the multilayer structure and hardness can be maintained for as long as 16 h at 700 deg C. This was found to be independent of the Cr content (multilayer wavelength) of the coatings. Oxidation behaviour involving isochronal thermogravimetric analysis (TGA), XRD and SEM revealed that all coatings exhibited weight gains of as little as 5% of that of TiN under similar conditions at 1000 deg C. The resistance to oxidation was found to be dependent on the Cr content, with the greatest effect occurring in the P sub Cr = 12 kW samples. Two very distinct regimes of oxidation were observed. Up to approx900 deg C, the rate of oxidation was very low (approx0.2 gm exp -2 in the case of the P sub Cr = 4 kW samples and 0.1 gm exp -2 in the case of the P sub Cr = 12 kW samples). Above this temperature, the oxidation rates increased markedly for all samples, with that of the P sub Cr = 12 kW being the least severe.