| Summary: | The article describes the effect of heat treatment on the structural-phase state and properties of a multilayer Cr-Al-Co-Y coating obtained by magnetron sputtering. Heat treatment was carried out at 400, 800 and 1000 °C. The study of the microstructure was carried out by electron microscopy with energy dispersive analysis and powder X-ray diffraction. The surface of the samples was studied by atomic force microscopy. The thickness of the Co-Cr-Al-Y coatings was 1.5–1.7 ± 0.2 µm. The obtained coatings are characterized by a hardness of 4.7–6.4 GPa. A distinctive feature of the layers is the absence of a crystalline structure in some areas of the coating. The main process occurring during the thermal treatment is the formation of a spinel-type phase. For a single-layer sample after heat treatment at 400 °C, it was not possible to fix extraneous reflections except for the reflections of the silicon substrate 111 and 220. For the rest of the samples, the appearance of reflections of a number of phases was noticed, such as: SiO<sub>2</sub>, CoO, AlSi<sub>0.5</sub>O<sub>2.5</sub> and CrAl<sub>0.4</sub>2Si<sub>1.58</sub>. An increase in the treatment temperature up to 800 °C did not lead to significant changes. In the case of the multilayer sample, the reflections of various impurity phases disappeared and the Co<sub>3</sub>O<sub>4</sub> phase was formed. For samples treated at 1000 °C, the formation of a spinel-type phase (Co<sub>3</sub>O<sub>4</sub>-CoCr<sub>2</sub>O<sub>4</sub>) was observed in all cases. Data on the structural-phase state and properties of the multilayer Co-Cr-Al-Y coating can be used to predict the nature of such coatings after heat treatment.
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