Influence of the addition of silicon on the structure and properties of chromium nitride coatings deposited by reactive magnetron sputtering assisted by RF plasmas

Abstract

CrN and Cr–Si–N films have been deposited by means of reactive magnetron sputtering in an Ar + N 2 mixture (20 and 10 sccm respectively) at a constant RF bias voltage of − 200 V. The silicon content of the films was controlled thanks to silicon coupons placed in the erosion track of the chromium target. The influence of the addition of silicon on the properties and on the structure of Cr–Si–N coatings is presented. It is shown that the high RF bias considered in this study favours the implantation of argon atoms into the coatings, associated to the re-sputtering of nitrogen atoms leading to the formation of very hard understoichiometric CrN and to internal compressive stress between 1 and 1.5 GPa. Then, the evolution of the composition and of the structure of the deposited coatings versus their silicon contents are presented thanks to GDOES and XRD analysis. The evolution of the hardness and of the Young's modulus versus the silicon content of the films exhibit a peak for a critical percentage of silicon (2.2 at.%), which is attributed to the formation of a nanocomposite structure. For this critical content of silicon, a basic model based on the Cr–Si–N ternary phase diagram and on an ideal 2D nanocomposite structure is proposed to calculate its fraction of amorphous phase. It is shown that the model calculations are in perfect agreement with the structure observed by means of high resolution transmission electron microscopy and that only a small amount of silicon (between 2 and 3 at.%) is needed for the formation of a nanocomposite structure in the Cr–Si–N system.