Study on the substrate surface micro-texturing/carburizing regulating the film-substrate adhesion and wear behavior of DLC coatings

Abstract

The diamond-like carbon films (DLC) coated on medical titanium alloy suffer from the problem of insufficient coatings adhesion due to thermal expansion mismatch, different wetting properties at the film/substrate interface. In order to enhance DLC coatings adhesion, the titanium alloy substrate surface was pretreated by laser texturing and carburizing with different texture densities and different laser carburizing powers. The adhesion and tribological properties of the laser textured (LTC), laser carburized (LCC), and hybrid laser textured and carburized (LTCC) DLC coatings were evaluated by scratch test, indentation test and wear test, compared with the only polished DLC coatings (PC). The results showed that the bonding strength of LTC, LCC and LTCC samples was about 1.52, 1.62 and 2.14 times higher than that of PC samples, and the best tribological properties were obtained for LTCC samples. Meanwhile, the density of micro-dimples and the power of laser carburizing significantly affect the adhesion and tribological properties. Among the dent densities studied, textured samples with a density of 30 % showed the lowest mean friction coefficient and wear rate. The critical force of the carburized DLC coatings was first rising and then falling as the laser carburizing power increased, and the bond strength of the film base reached the maximum at a carburizing power of 10 W. The texturing treatment results in an improvement of the specific surface area of the substrate and the laser carburizing treatment results in an increase of the coating nucleation density and decrease of coatings graphitization degree, both improving the coatings adhesion and triboligical behavior.