High-temperature oxidation of CrAlYN coatings: Implications of the presence of Y and type of steel

• Published in: Surface & coatings technology Vol. 354; pp. 203 - 213
• Main Authors: Rojas, T.C., Domínguez-Meister, S., Brizuela, M., Sánchez-López, J.C.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.11.2018; Elsevier BV
• Subjects: Aluminum oxide; Austenitic stainless steels; Chromium nitride; Coatings; Columns (structural); Corrosion; Electron energy; Electron energy loss spectroscopy; Energy transmission; Grain boundaries; High temperature; High temperature corrosion; Microstructural analysis; Mixed oxides; Oxidation; Oxidation resistance; Phase transitions; Rare earth elements; Scale (corrosion); Sputtered films; Steel; STEM; Structural steels; Substrates; Thermal stability; Trace elements; Transmission electron microscopy; Oxidation; Sputtered films; Rare earth elements; Steel; High temperature corrosion; STEM
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2018.09.020

Nanolayered CrAlN and CrAlYN/CrAlN (average contents of Al ≈ 25 at.% and Y ≈ 1.6 at. %) coatings are deposited on M2 and 316 steel substrates and heated to 1000 °C in air for 2 h to study their oxidation mechanism, the thermal stability and the reactive element (RE) effect of yttrium. CrAlN on M2 develops a Cr2O3/Al2O3 passivation layer that preserves in high degree the fcc-CrAlN structure however iron ions leave the substrate and travel to the surface along the column boundaries. The CrAlYN/CrAlN coatings deposited on steels are not stable at 1000 °C, and the initial fcc-CrAlN phase is partially transformed to hcp-Al(O)N and Cr-Fe phases (M2) and Cr2N and Al2O3 (316). The addition of Y changes the predominant scale growth direction. Inward oxygen diffusion becomes dominant but a reduction of the oxide scale thickness as compared to CrAlN is not observed. The advanced microstructural analysis made by transmission electron microscopy combined with electron energy-loss spectroscopy determined that yttrium migrates mainly to the oxide scale (forming mixed oxides with substrate elements - V and Mo, either as dispersed particles or segregated at the grain boundaries) in M2, and to the oxide interface and column boundaries (forming Al-Y oxides and YN, respectively) in 316 steel. The benefits of addition of Y in improving the oxidation resistance are discussed comparatively with literature data. The RE effect of yttrium is thus observed to be dependent on the substrate, film architecture and composition. [Display omitted] •The RE effect of Y in CrAlN films has been demonstrated using advanced TEM techniques.•Corrosion products, yttrium location and chemical state depend on the type of steel.•Y diffuses preferentially to the oxide scale and gets oxidized in M2 steel.•YN formed at the column boundaries blocks the iron outward diffusion in 316 steel.•CrAlYN transforms to hcp-Al(O)N in M2 and hcp-Cr2N + Al2O3 in 316 steel.