Microstructure, mechanical property and thermal stability of diamond-like carbon coatings with Al, Cr and Si multi-doping

Abstract

In this paper, AlCrSi atoms were co-doped into DLC coatings by using a high power impulse magnetron sputtering combining with an anode-layer linear ion beam. The doped AlCrSi contents were controlled via adjusting the Ar fraction in the sputtering gas mixture of Ar and C2H2. The influences of the AlCrSi multi-doping on the composition, microstructure, residual stress, mechanical property and tribological behavior of the as-deposited DLC coatings were studied systemically by using EDS, XPS, TEM, stress-tester, nanoindentation and ball-on-plate tribometer as a function of the Ar fraction. The thermal stability of the coatings was also researched by a vacuum heat treatment with various temperatures. The results show that the carbide former Cr preferred to form hard carbide components which were conducive to the hardness of the coatings, while the weak carbide former Al dissolved in the DLC matrix as metallic state, which can effectively released the stress of the DLC coatings. The doped Si would bond with sp2-C to form sp3 CSi, and thus maintained the sp3-C structure stability and improved the thermal stability of the coatings. Accordingly, the DLC coatings with AlCrSi multi-doping not only exhibited relatively low residual stress and high hardness, but also showed a high thermal stability over 500°C. It was believed that the AlCrSi multi-doping may be a good way for improving the comprehensive properties of the DLC coatings.