Residual Stresses 2018 – ECRS-10 Materials Research Forum LLC Materials Research Proceedings 6 (2018) 131-136 doi: http://dx.doi.org/10.21741/9781945291890-21 Content from this work may be used under the terms of the Creative Commons Attribution 3.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under license by Materials Research Forum LLC. 131 Evaluation of Residual Stresses in PVD Coatings by means of Tubular Substrate Length Variation Harri Lille 1,a,* , Alexander Ryabchikov 1,b , Jakub Kõo 1,c , Eron Adoberg 2,d , Valdek Mikli 2,e , Jakob Kübarsepp 2,f , Priidu Peetsalu 2,g 1 Institute of Forestry and Rural Engineering, Estonian University Life of Sciences, Kreutzwaldi 5, 51014 Tartu, Estonia 2 Department of Mechanical and Industrial Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia a harri.lille@emu.ee, b alexander.ryabchikov@emu.ee, c jakub.koo@emu.ee, d eron.adoberg@ttu.ee, e valdek.mikli@ttu.ee, f jakob.kubarsepp@ttu.ee, g priidu.peetsalu@ttu.ee Keywords: TiAlN Hard PVD Coating, Residual Stresses, Length Variation Abstract. The aim of the study was to determine macroscopic residual stresses in PVD coatings. The device for measurement of the length of the substrate was improved, where a change in tube length was reduced to the deflection of the middle cross-section of the elastic element whose deformation was measured by four strain gauges. The formulas for calculation of residual stresses are presented. For comparison a unilateral coating was deposited on a vertically fixed plate using the conventional curvature method. As an application, residual stresses in hard PVD TiAlN coatings were investigated. The microstructure and thickness of the studied coatings were investigated by means of scanning electron microscopy (SEM) in Zeiss EVO MA-15. The mean values of compressive residual stresses determined by both methods, for the studied coatings, were very high (3.1-6.5 GPa), irrespective of coating thickness, and practically equal with the measurement uncertainty of the method. The developed tube length variation method is reliable and applicable for determination of residual stresses in PVD coatings. Introduction Physical Vapour Deposition (PVD) coatings are used inter alia for blanking, punching and cutting applications and can be deposited both on plain and more complex surfaces [1, 2]. It is wellknown that residual stresses arising in coatings during the deposition process have an important effect on the service life of the coating through influencing its mechanical and tribological properties and adhesion. The aim of the study was to determine macroscopic residual stresses in coatings vapoured on a vertically fixed cylindrical surface, using the deformation method, through measurement of the longitudinal length variation of the thin-walled tube, as well as to validate the results obtained with the conventional curvature method using the plate as the substrate. One batch of vertically fixed plates was prepared by depositing a unilateral coating on the front surface and the other batch of plates, by depositing it on the back surface. Thus a considerable amount of the vapoured target material was deposited on the fixing device as well [3]. On the other hand, using the tubular substrate, most of the coating was deposited on the outer surface of the tube (a small part of the coating was deposited on the nozzle) it is possible to estimate the values of residual stresses in coatings on cylindrical surfaces (e.g. cutting tools [4]). The measuring device for determination of the longitudinal length change of the substrate was improved (Fig. 3), where tube length variation was reduced to the deflection of the middle cross- section of the elastic element whose deformation was measured by four strain gauges [5]. As an example of application, residual stresses were measured in hard PVD TiAlN coatings which are