Evaluation of residual stresses in PVD-coatings. Part 2

Abstract

The values of residual stresses in PVD-coatings of titanium, aluminum and niobium nitrides are determined by the flexible specimen method. An experimental-and-calculation procedure for separating the structural and thermal components of residual stresses is proposed that allows one to determine the thermal expansion coefficients of the coating materials and a general level of residual stresses in coatings on a substrate of any material. The dependence of the residual stress on the roughness of the substrate surface is established. The possibility of adjusting the level of residual stresses in coatings by the discrete surface topography formation is shown.Keywords: vacuum plasma coatings, residual stresses, roughness, thermal and structural components of the residual stresses, discrete topography.Introduction. Plasma vacuum deposited (PVD) nitride-based coatings exhibit high hardness and good adhesion to substrates. Owing to their considerable wear-and heat resistance, these are widely used to enhance the performance of cutting and deforming tools, friction pair components, gas turbine engine (GTE) blades. The analysis of the data given in the literature shows that these coatings exhibit considerable residual compressive stresses whose level is from hundreds of megapascals (MPa) to a dozen of gigapascals (GPa) [1-6]. The residual stresses are induced by both the difference in the thermal expansion coefficients of the substrate and coating materials (the thermal component) and the interaction between the growing crystallites (the structural component) [1,7].As argued by the authors of [2,8], the coating stresses due to the structural component (the coating growth stresses) are independent of the substrate material, and the difference between the level of residual stresses in coatings deposited on different substrates is dependent on the thermal component. It is the high level of residual compressive stresses that the crack growth resistance, wear-resistance and corrosion resistance of surfaces modified by vacuum plasma coatings can be related to [9][10][11]. As noted in [12], a high level of residual compressive stresses retards the crack formation processes in coatings during operation of cutting tools, especially under conditions of interrupted cutting. The presence of considerable residual compressive stresses affects positively the characteristics such as fatigue limit [13] and yield strength [14]. At the same time, owing to a high level of residual compressive stresses, the coatings become more brittle, which can result in their spontaneous delamination even prior to the beginning of the operation or to the breakage of adhesion between the substrate and coating during the operation [15][16][17][18][19][20].In this connection, it is necessary to determine the possibilities on the adjustment of the level of the residual compressive stresses in coatings. Attaining this goal is possible by way of improving the coating deposition process and creating the suitable surface architecture. Commonly used methods for adju...

Influence of the Thickness of a Nanolayer Composite Coating on Values of Residual Stress and the Nature of Coating Wear

“…The internal residual stress that forms in coatings during their deposition has been a subject of research for a long time. Detailed analyses of the methods for studying stress in coatings and thin films are contained, in particular, in [1][2][3][4]. The measurement of stress in a coating with a thickness of only several micrometers, which includes various phases that differ in their properties, presents a certain challenge.…”

Thermal Barrier Coatings—A State of the Art Review

“…The residual stress generated in the coating during the deposition phase can result in premature failure of the coating by spallation and cracking [93,94]. The initial stress state in the coating must be evaluated to predict the behavior of the coating under cyclic thermal or isothermal loading conditions [95,96]. Destructive and non-destructive techniques have been developed to measure the residual stress in metallic and ceramic coatings.…”

Tests for Applying Coatings Based on Aluminum and Silver on Alnico Alloys

“…Vapor deposition coating technology is a process that causes the formation of coating materials on the surfaces of solids as a result of specific exploitation of gaseous, vaporous or plasma states [1][2][3][4][5][6]. One of the unconventional techniques for producing coatings is the method of diffusion bonding of thin films with the base material, thereby producing coatings [7,8].…”