Preparation Of Superhard Functionally Graded Tetrahedral Amorphous Carbon Coatings By Pulsed Laser Deposition

Abstract

AbstractThe internal compressive stress as large as 10 GPa has been the major stumbling block for preparation of relatively thick superhard tetrahedral amorphous carbon (Ta-C) films. We have successfully deposited Ta-C films as thick as 1000 nm by mechanical doping to reduce and alleviate the level of internal compressive stresses. In this paper, we reported the preparation of functionally graded Ta-C coatings by pulsed laser deposition. The thickness of the Ta-C films with significantly improved adhesion was measured to be up to 1500 nm. The concentration of foreign atoms such as silver, copper, silicon and titanium was decreased away from the coating/substrate interface, and the surface layer was pure Ta-C. Nanoindentation measurements were performed on the coatings. Nanohardness as high as 65 GPa and Young‘s modulus as large as 600 GPa were obtained for the functionally graded Ta-C films. Micro-Raman measurements and microstructural analysis by transmission electron microscopy was carried out to acquire information about the bonding environment and atomic structure of the coatings as a function of foreign atoms. The results were discussed in combination with theoretical models associated with the prediction of elastic properties of amorphous carbon networks.