[en] Highlights: • Cr-CrN multilayers are deposited by MS-PVD under controlled condition; • Residual stress profiles were evaluated by FIB-DIC micro ring-core milling; • Scratch test shows dependence of adhesion on residual stress profile, without changes in overall hardness and microstructure Compressive residual stress in hard coatings can improve adhesion and in-service toughness, since they can inhibit crack nucleation and propagation. However, the role of through thickness residual stress profile is not fully understood. This is because of (a) lack of knowledge of stress evolution mechanisms and (b) limitations of experimental techniques used for stress profiling. The present work deals with design, deposition and characterization of Cr-CrN multilayer coatings, produced by Magnetron Sputtering Physical Vapour Deposition (MS-PVD), with the purpose to understand the effect of through thickness residual stress profile on coating adhesion. An automated optimisation algorithm was used to determine the desired residual stress through-thickness profile for a range of contact loading situations. On the basis of modelling activities, three different Cr-CrN multilayers were produced, with the aim of obtaining different stress gradients, as measured by incremental micro-scale focused ion beam (FIB) ring-core method, while keeping the same average stress value and same average hardness in the film. Results show a significant correlation between the observed residual stress profiles and scratch adhesion, where different optimal stress profiles are identified for different loading conditions. This is a major step with respect to previous literature, where scratch adhesion in hard coatings was only correlated to the average stress in the film, but not to the stress gradient within the film thickness. Here, we show that a lower interfacial compressive stress and a reduced through thickness stress gradient gives improved scratch adhesion, when using 10 μm and 200 μm sphero-conical indenters.

[en] Chemically inert coatings on Havar"® entrance foils of the targets for ["1"8F] production via proton irradiation of enriched water at pressurized conditions are needed to decrease the amount of ionic contaminants released from Havar"®. During current investigation, magnetron sputtered niobium and niobium oxide were chosen as the candidates for protective coatings because of their superior chemical resistance. Aluminated quartz substrates allowed us to verify the protection efficiency of the desirable coatings as diffusion barriers. Two modeling corrosion tests based on the extreme susceptibility of aluminum to liquid gallium and acid corrosion were applied. As far as niobium coatings obtained by magnetron sputtering are columnar, the grain boundaries provide a fast diffusion path for active species of corrosive media to penetrate and to corrode the substrate. Amorphous niobium oxide films obtained by reactive magnetron sputtering showed superior barrier properties according to the corrosion tests performed. In order to prevent degrading of brittle niobium oxide at high pressures, multilayers combining high ductility of niobium with superior diffusion barrier efficiency of niobium oxide were proposed. The intercalation of niobium oxide interlayers was proved to interrupt the columnar grain growth of niobium during sputtering, resulting in improved diffusion barrier efficiency of obtained multilayers. The thin layer multilayer coating architecture with 70 nm bi-layer thickness was found preferential because of higher thermal stability. - Highlights: • Diffusion barrier efficiency of niobium, niobium oxide and their multilayers was studied. • The intercalation of niobium oxide layers interrupted the columnar grain growth of niobium. • The bilayer architectures influenced the stability of the multilayer coatings. • The thin layer multilayer coating with 70 nm double-layer was found superior.