Investigation of the effect of Si content on the structural, mechanical, and tribological properties of TiAlN/AlSi protective multilayers

Abstract Titanium aluminum nitride and aluminum silicon alloys (TiAlN/AlSi) or for simplicity (TAN/AS) bilayer system were deposited on glass and piston aluminum substrates by following three steps. First, AlSi films realized by thermal evaporation with different Si content (7, 10, 13, 22) %. Then, TiAl films were deposited on AlSi layers using a reactive DC magnetron sputtering system, and finally the realization of TAN/AS multilayers were done by nitriding via Direct Current Plasma Nitriding (DCPN) in a custom setup, with pure nitrogen gas. For each sample, the structural properties like phase’s formation and vibration modes were investigated by X-ray diffraction and Raman spectroscopy, while AFM microscopy investigated surface topography. The mechanical and tribological properties in terms of hardness and friction coefficient were determined using the nanoindentation technique and tribometer. It has been found that all the coatings TAN/AS have crystalline structures with the presence of TiAlN, TiN, AlN, TiAl, and α-Al phases. Raman spectroscopy reveals the appearance of TO/LO, 2O, and 2TO/LO modes for all layers. AFM images show that the coatings have low roughness, Ra values decrease from 17.3 nm for 7 % Si to 5.5 nm for 13 % Si and increases to 9.9 nm at 22 % Si. The grain size exhibits a reversed behavior compared to that of roughness. The hardness and Young modulus reach their optimum values at 13 % Si with no respect to Hall–Petch law. The friction coefficient of TAN/AS coatings decreases with Si content and reaches its lowest value (<0.1) at 22 % Si as a potential protective layer.