Hard and dense diamond like carbon coatings deposited by deep oscillations magnetron sputtering

Abstract

Recent developments in the automotive industry to improve engine efficiency and minimize pollutant emissions are driving the need for higher operating temperatures and loading densities in internal combustion engines. Future engines for internal combustion engines will require coatings with increased temperature stability (up to 500°C) and wear resistance as compared to present day solutions. Hard tetrahedral DLC coatings (ta-C coatings) very low coefficient of friction and performed very well under mixed and boundary lubrication, and, thus, they are very attractive for automotive industry. In this work, DLC coatings were deposited by deep oscillations magnetron sputtering (DOMS), a variant of high power magnetron sputtering (HiPIMS). The main objective is to increase the sp3 content in the films, as compared to d.c. magnetron sputtering (DCMS), and thus extend their operating range to higher temperatures. Increasing the bias voltage results in denser and smoother films with increasing hardness, as measured by nano-indentation, and increasing mass density, as measured by x-ray reflectivity. Accordingly, the UV Raman spectroscopy analysis of the films shows that the sp3/sp2 ratio in the films increases with increasing substrate biasing. However, the sp3 bonds convert back to sp2 upon annealing. Never the less, a significantly higher amount of sp3 bonds is formed in the DLC films deposited by DOMS, as compared to the DCMS ones, showing that DOMS is a promising path for the development of hard DLC films.