A comprehensive study of CrN/AlCrN-based monolayers and architected multilayers

• AlCrN monolayers were optimized by varying temperature and bias voltage. • Multilayers were optimized by varying interfaces number and bilayer thickness. • The optimized coatings exhibit low and similar thermal conductivity. • Both the interfaces number and thickness influence coatings performance. Cr, CrN, and AlCrN monolayers and Cr/CrN/AlCrN multilayers were deposited on rough/mirror-polished tungsten carbide and silicon substrates by Direct Current magnetron sputtering. The multilayers were developed based on the optimized monolayers. In this paper, we introduce and discuss the optimization steps and performances of the AlCrN monolayers and the CrN/AlCrN-based multilayers. The influence of the deposition temperature and substrate bias voltage on the coating properties, the number of interfaces, and the thickness of CrN/AlCrN pairs were systematically studied for the monolayers and multilayers, respectively. The composition of the monolayers was determined by energy dispersive x-ray spectroscopy and verified by x-ray photoelectron spectrometry. Scanning electron microscopy observations permitted to define the microstructure and thickness of the coatings. Ball-on-disc tests were realized to determine the coefficient of friction and wear rate. The hardness and elastic modulus were calculated from nanoindentation tests. The adhesion was quantified by scratch-tests. The thermal conductivity measurement was obtained by Modulated Photo Thermal Radiometry. The optimized coatings have a dense and homogeneous surface morphology on WC Co substrates, are well crystallized, present a grain size lower than 10 nm, a friction coefficient of 0.5, and low wear rates. The results indicate that the optimal AlCrN monolayers are obtained at 300 °C/-250 V. The optimized AlCrN monolayers also have tensile and mostly compressive stresses, a hardness of 25.8 GPa, an elastic modulus of 170 GPa, and a Lc2 critical load of 58 N. The optimal multilayers are the one with decreasing CrN/AlCrN pairs thickness from substrate to top layer and the one with a doubled number of interfaces. The multilayers have low residual stresses from -47.7 MPa to 44.8 MPa, a hardness from 16.1 to 24.8 GPa, an elastic modulus from 429 to 670 GPa, a Lc2 critical load from 47 to 52 N, a low and similar thermal conductivity from 1.95 to 2.42 W·m -1 ·K -1 .