OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 2 2023 Introduction With the development of materials production technology for cutting tools, press molds, engine components, and other mechanical components, mainly hard coatings are used [1, 2]. Metal nitrides such as chromium, niobium, zirconium, tantalum, titanium, or its combinations are primarily used as coating materials [3–5]. Such coatings are able to withstand the high load and temperature that characterize the operation of the cutting tool. It is worth noting that coatings are used not only to provide the necessary characteristics of cutting tools; as studies show, some coatings such as CrN can be used as a coating for zirconium alloy for use in fuel accident-resistant materials [6, 7], and ZrC/TaC, Ru-Al/Ru-Si-Zr finds applications in the aviation industry and gas turbine blades [8, 9]. In this regard, the main methods of coating deposition can be named as reactive magnetron sputtering [3, 10], vacuum brazing [11], thermal spraying [12], high-speed physical vapor deposition [13, 14], and pulsed electro deposition [15]. In this work, the vacuum arc plasma deposition method is used [16]. Despite the wide use of nitride coatings in the cutting tools manufacture, the limits of its application, and properties acquired after exposure to certain conditions are being investigated. In most cases, corrosion resistance [17] and oxidation processes [10, 18] at temperatures above 1,000 °C are studied. The authors [17] found that multilayer Cr/CrN coatings on a Zr-4 zirconium alloy substrate exhibit good resistance to steam oxidation with a decrease in the thickness of the multilayer coating layers. In turn, the primary task of characterizing the coating process is not described in the literature. The problem lies in the complexity of depositing thick multilayer, multicomponent coatings with different physical characteristics. First of all, this concerns the coefficient of linear thermal expansion (CLTE) of the components of the multilayer coating. Since the process of deposition and operation of coatings involves temperature exposure, the components of the coating with different CLTEs will eventually be prone to cracking, further destruction, and failure of the products. The aforementioned works suggest that it is important not only to understand the characteristics and properties of nitride coatings, but also the kinetics of the structural behavior of multilayer coatings obtained through thermal action in air. Therefore, the purpose of this work is to in-situ study the patterns of structural changes in CrN/ZrN multilayer coatings deposited on a 92 wt.% Co-8 wt.% WC substrate by vacuum-arc plasma deposition after thermal testing in air with an exposure temperature of 30 to 750 °C. The conducted research will be useful for developing knowledge on the behavior of materials with various physical properties in multilayer coatings at elevated operating temperatures in engineering applications, such as cutting tools. The study is based on the task of investigating the structural-phase composition in CrN/ZrN multilayer coatings during the heating of the substrate of 92 wt.% Co-8 wt.% WC alloy with a multilayer coating consisting of alternating nitride layers of CrN and ZrN. The aim of this study is to conduct in-situ investigation of ZrN/CrN multilayer coatings using X-ray structural analysis with synchrotron radiation and to qualitatively assess the behavior of microstrains in multilayer coatings obtained by plasma-assisted vacuum arc method on a substrate made of 92 wt.% Co-8 wt.% WC alloy under temperature exposure up to 750 °C. The result is to provide the opportunity to determine changes in the characteristics of multilayer coatings during heating, such as the change in the lattice parameter of each component of the coating separately, the possibility of determining the coefficient of thermal expansion of the coating components, and the qualitative determination of microstrains, as well as the possibility of forming recommendations for further application of multilayer coating deposition technology with specified characteristics based on the conducted analysis. Methods and materials Experimental specimens subjected to heating during synchrotron investigations were used with ZrN/CrN multilayer coatings applied to a substrate of 92 wt.% Co-8 wt.% WC alloy using a plasma-assisted vacuum arc method, obtained at different rotation speeds of the table and substrate holder in the planetary coating deposition scheme shown in Fig. 1. For the experiment, two coating deposition modes were selected: table rotation speed of 0.5 rpm (ZrN/CrN-0.5 specimen) and 8.0 rpm (ZrN/CrN-8 specimen).
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