Influence of Ag additions on the structure, mechanical properties and oxidation behaviour of Cr-O coatings deposited by HiPIMS

• Published in: Surface & coatings technology 2018-04, Vol.339, p.167-180
• Main Authors: Fernandes, F., Yaqub, T.B., Cavaleiro, A.
• Format: Article
• Language: English
• Subjects: Agglomerates; Annealing; Composite structures; Cr-O-Ag self-lubricant coatings; Crystal structure; Crystallinity; Crystallization; Deposition; Diffusion coating; Diffusion coatings; Diffusion layers; In-situ high-temperature XRD; Magnetic properties; Magnetron sputtering; Mechanical properties; Morphology; Oxidation; Oxidation resistance; Oxide scale; Reaction kinetics; Recrystallization; Silver; Structure; Thermogravimetric analysis
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2018.02.025

Here, we investigate the influence of Ag additions on the properties of Cr-O coatings deposited by magnetron sputtering. The deposition rate of Cr-O coating is 1.6 times higher than a single Cr coating, taken as reference, deposited with identical conditions. Incorporation of Ag in the Cr-O coating increases the deposition rate. Transition from a dominant columnar to a very compact morphology, as well as from crystalline to amorphous structure, was observed with the O addition. However, no morphological changes were observed with Ag additions. Annealing at temperature ≥ 500 °C promotes the crystallization of Cr-O and Cr-O-Ag coatings, i.e. the formation of a crystalline composite structure, formed by: Cr, Cr2O3 and Ag phases, the later in the case of Cr-O-Ag coatings. The increase of coatings crystallinity improved the mechanical properties. Thermogravimetric analysis showed that O and Ag additions to Cr have no influence on the onset point of oxidation. The oxidation kinetics of the Cr-based coatings is controlled by the outward diffusion of Cr ions through a top Cr2O3 layer. A dual oxide layer was formed for Cr-O and Cr-O-Ag coatings, when exposed to a continuous increase of the temperature up to 1200 °C. A compact layer of Cr2O3 grows on top of the coating, due to the Cr ions outwards diffusion, leaving behind a porous layer formed by Cr2O3 grains resulting from the recrystallization process, together with Ag agglomerates inside the empty porous zones. [Display omitted] •Effects of Ag additions on CrO coatings deposited by HiPIMS were investigated.•Compact, non-stoichiometric and amorphous CrO(Ag) coatings were deposited.•Ag additions to CrO coating did not change its microstructure nor the mechanical properties•Crystallization of the coatings was attained for annealing temperatures ≥500 °C•Oxidation of these coatings was controlled by Cr ions diffusion though a Cr2O3 layer.