Influence of Al and Y content on the oxidation resistance of CrAlYN protective coatings for high temperature applications: New insights about the Y role

• Published in: Journal of alloys and compounds 2019-01, Vol.773, p.1172-1181
• Main Authors: Rojas, T.C., Domínguez-Meister, S., Brizuela, M., Sánchez-López, J.C.
• Format: Article
• Language: English
• Subjects: Aluminum; Catalytic oxidation; Chemical compounds; Diffusion coating; Direct current; High speed tool steels; High temperature; High temperature corrosion; Microstructure; Nitride materials; Oxidation resistance; Protective coatings; Rare earth elements; Scale (corrosion); Sputteered films; Substrates; Thermal resistance; Thermal stability; Transmision electron microscopy techniques; Yttrium
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2018.09.280

CrAlYN hard coatings with two different average Al contents: ∼16 at.% and ∼25 at.%, and Y concentration varying between 1.2 and 5.7 at.% were deposited by direct current reactive magnetron co-sputtering of mixed Cr-Al and Y targets on commercial M2 steel substrates. The samples were heated to 1000 °C in air during 2 h to study their oxidation resistance and thermal stability. The Y content is critical and the coatings present different behaviour depending on the Al content. The best oxidation resistance and thermal stability are obtained for the coating with ∼16 at.% Al and 3.4 at.% Y. The initial film microstructure and the cubic phase (fcc-CrAlN) were retained, and a thin (Cr,Al)2O3 oxide protective scale was formed. At lower Y content (1.2 at.%) iron, from the substrate crosses the coating, while a higher content (4.6 at.%) avoided the iron diffusion at the expense of a thicker oxide scale with new oxide phases. The coatings with higher Al content (∼25 at. %) were not thermally stable at 1000 °C. A good oxidation resistance was obtained for 2.6 at.% of Y although new phases (hcp-AlN and Cr-Fe) were formed. Higher amount of yttrium (∼5.7 at. %) led to the complete oxidation of the coating. [Display omitted] •Y atoms diffuse and segregate at the scale grain boundaries and interface (RE effect).•Y diffused to the column boundaries hindering the Fe migration from the substrate.•CrAl (16%)Y(3%)N presents good oxidation resistance and stability at 1000 °C/2 h.•Al (25%) shows higher degree of fcc-CrAlN decomposition and oxidation (Y > 3 at.%).•Excess of Y favors oxygen inward penetration through Y2O3 and Al5O12Y3 and AlYO3.