TiSiN(Ag) films deposited by HiPIMS working in DOMS mode: Effect of Ag content on structure, mechanical properties and thermal stability

TiSiN(Ag) coatings with Ag contents ranging from 0 to 29 at.% were designed as promising materials to allow long term solid lubrication during dry machining operations. Here, we report the influence of Ag additions on the properties of TiSiN(Ag) films deposited by high power impulse magnetron sputtering- HiPIMS, working in deep oscillation magnetron sputtering mode -DOMS. Introduction of silver pellets on the target progressively increases the Ag concentration on the films, influencing the deposition rate, structure and morphology of the films. All the coatings display crystalline peaks assigned to a TiN fcc NaCl type structure. Ag additions to the reference TiSiN film, significantly broadens the TiN diffraction peaks and abruptly decreases the grain size of the TiN crystallites from 24 nm to 11-7 nm. Grain size was then found to be independent of the silver content on the films. Hardness and Young's modulus of the coatings decreased with increasing Ag additions mainly due to the increase of this soft phase on the microstructure. An increase in the peak power was observed when 6 at.% Ag was added which revealed a transition from a columnar to a very compact morphology, a decrease of the deposition rate and an increase of the lattice parameter for this coating. A reverse in the morphology is then perceived for the higher Ag concentration (29 at.%). Annealing treatment didn't present any significant changes in the structure/phase composition or mechanical properties of the coatings. Elemental maps and profiles allowed perceiving the formation of a very thin dual layer where a top Ag rich layer is formed due to the diffusion of silver from the Ag deficient TiSiN layer below.