Effect of Cryogenic Treatment on Film-substrate Bonding Strength of DLC Film/High-speed Steel

Abstract

In order to investigate the effect of cryogenic treatment (CT) on film-substrate bonding strength, 2µm thick DLC film was deposited on quenched W9 high-speed steel by unbalanced magnetron sputtering technique followed by CT at-196℃ for 30 hours. Samples before and after CT were characterized respectively by using AFM, indentation, scratch, SEM combined with EDS and XRD analysis. The results show that the film-substrate bonding strength of DLC film/quenched W9 high-speed steel is improved by CT for 30h. Additionally, the structure of substrate is refined and carbon content in substrate surface of interface significantly increases. Moreover, CT allows the occurrence of martensitic transformation and decomposition increasing substrate grain boundary which facilitate the interface diffusion of carbon from DLC to the substrate. The element C diffusing to grain boundaries of the substrate surface is proposed to form new carbides which enhance the pinning effect of DLC film on the substrate.