Enhanced mechanical and tribological properties of hydrogen-free DLC coating by introducing SiAl interlayer

This study investigated the effects of various Si, Al, and SiAl interlayers on the mechanical and tribological properties of hydrogen-free DLC coatings deposited on 316L stainless steel (316LSS). Using a Si single-interlayer resulted in high oxygen concentration at the DLC interface , adversely increasing residual stress and degrading adhesion. However, the SiAl interlayer significantly enhanced the mechanical properties of DLC , increasing its hardness from 14.5 to 17.8 GPa. In addition, the SiAl interlayer drastically reduced the high compressive stress of non-interlayered DLC from 0.68 GPa to 0.23 GPa, while the Si interlayer only slightly decreased it to 0.61 GPa. The Si and SiAl interlayers improved the tribological properties of DLC to withstand loads at 5 N, 7 N, and 10 N. In contrast, non-interlayered DLC and Al/DLC coatings peeled off under 7 N. Notably, SiAl/DLC illustrated better tribological properties than Si/DLC. Under 10 N, Si/DLC coating showed the coefficient of friction COF, wear rate, and Hertzian pressure at 0.13, 4.43 (10 −7 mm 3 /N.m), and 1.45 GPa, respectively, while those of SiAl/DLC coating were 0.12, 3.41 (10 −7 mm 3 /N.m), and 1.39 GPa. Meanwhile, the SiAl/DLC coating also maintained a high lubrication effect of the tribo-film, which favored excellent tribological properties. These findings identified that introducing SiAl interlayer could be a strong strategy to improve both the mechanical and tribological properties of hydrogen-free DLC coatings on 316LSS. • Incorporating SiAl interlayer improved the hardness and elastic modulus of DLC coating. • Introduced SiAl interlayer benefited robust bonding interface between DLC and 316 L stainless steel substrate. • SiAl/DLC coating demonstrated a superior tribological behavior under load of 10 N. • Formed thick tribo-film under higher load of 15 N favored a low COF despite the severe wear track in SiAl/DLC coating.