Duanjie Li

Advanced protective coatings providing high resistance to solid particle erosion as well as corrosion require system designs that combine the controlled dissipation of impact energy with the suppressed diffusion of corrosive media. In the present work, we propose and investigate a coating architecture benefiting from a “trampoline” energy-damping effect in which a hard TiSiC:H layer on top of an elastic a-SiC:H underlayer is prepared by plasma enhanced chemical vapor deposition on aerospace-grade titanium (Ti6Al4V) alloy and stainless steel 410 (SS410) substrates provided with a Cr adhesion layer. In the first part of the work, we study the effect of hydrogen in the individual a-SiC:H films (determined by elastic recoil detection) on their morphology (using scanning electron microscopy) and the mechanical and tribological properties. The films exhibit a highly advantageous combination of properties such as high hardness (>20 GPa), high elastic recovery of up to 80%, low friction coefficient (μ = 0.15 against alumina counterpart), and excellent resistance to plastic deformation and elastic resilience, expressed by the hardness (H), reduced Young's modulus (Er), and the H/E, H3/Er2, and H2/Er ratios. In particular, the measured elastic strain-to-failure of the coatings reached an unusually high value of H/Er > 0.2, thus exceeding the super-elastic limit. Simultaneously, the a-SiC:H films provided an excellent corrosion and wear protection documented by a corrosion current that was found 103–104 times lower and a wear rate that was 34 times lower compared to the values for the bare SS410 substrate. When a top TiSiC:H layer (H = 30 GPa) was applied to complete a total thickness of 25 μm, the TiSiC:H/a-SiC:H system reduced the solid particle erosion rate (Al2O3 microparticles 50 μm in diameter, speed of 36 m/s, and 90° impact angle) by a factor of 37 for films exhibiting a composite H/E ratio of 0.26. The results of the present work show that hard and highly elastic a-SiC:H-based multilayer coating systems with selectively controlled mechanical, tribological, and corrosion properties are promising candidates for the protection of metallic materials in harsh environments.

The nanocomposite TiC/a-SiC:H/a-C:H (presented as Ti-Si-C) coatings attract considerable interest due to their possible applications such as wear protective coatings, diffusion barriers, and materials for solar cells and electrical contacts. In order to explore new film properties and open new opportunities, in the present work, we prepare a series of C-rich Ti-Si-C coatings with different Si and C concentrations using plasma enhanced chemical vapor deposition, and we systematically investigate the effect of elemental composition on the microstructure, and on the mechanical, tribological and electrochemical properties. XRD and XPS analyses demonstrate that the Ti-Si-C coatings mainly consist of nanocrystalline (nc-) TiC embedded in amorphous (a-) SiC:H and a-C:H matrices. Ti-Si-C coatings with a high Si concentration possess enhanced mechanical properties (high hardness), while those with additional C exhibit superior tribological behaviors. The increase of Si and/or C concentrations leads to a grain size refinement of the TiC nanocrystals and to an expansion of the amorphous phase. This in turn substantially enhances their corrosion resistance. Ti-Si-C coatings with the highest Si or C contents exhibit the best corrosion performance among the tested samples by improving the corrosion resistance of the SS410 substrate by a factor of ∼400.