The Microstructure and Properties of Niobium-doped Diamond-like Carbon Thin films

Abstract

Doping diamond-like carbon (DLC) thin films with metals is an excellent way to reduce stresses in DLC films and improve their adhesion to artificial hip joint biomaterials. This improvement would translate to improving the implants' overall performance and ultimately extending their service life. However, limited investigation has been reported on Nb-doped DLC films in the literature. This research attempts to fill the research gap to understand the effect of Nb doping on the structure and properties of these films.

Nb-doped DLC films were deposited on silicon (100) and biomedical-grade CoCrMo alloy substrates by radio-frequency magnetron sputter technique with different Nb contents. The structure of the deposited films was characterized using X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Rockwell C indentation, nanoindentation, optical profilometry, and pin-on-disc wear testing were used to obtain the mechanical and tribological properties of the films. The corrosion behavior of the films in NaCl were also investigated using a potentiostat. It was found that the doped films show a nanocomposite structure with DLC as matrix and nanocrystalline Nb or Nb-C as the dispersed phase. As Nb incorporation decreases sp3 bonded carbon bonds in the thin films, the hardness of the doped DLC films is slightly reduced. Despite this slight reduction in hardness, Nb doping drastically reduces the compressive stress in the DLC films and thus enhances the films' adhesion to the substrate. Additionally, Nb-doped DLC films reduced the wear of polymer counterparts compared to the CoCrMo alloy without coating or DLC film without doping. Likewise, the corrosion resistance of the coated substrates, especially those with Nb-doped DLC, was at least 82 % higher than the uncoated ones.