AVS 50th International Symposium
    Advanced Surface Engineering Monday Sessions
       Session SE-MoA

Paper SE-MoA6
DLC and CNx Coatings Produced by Pulsed Laser and Filtered Vacuum Arc Techniques

Monday, November 3, 2003, 3:40 pm, Room 323

Session: Hard Coatings: Preparation, Properties, Wear, and Nanotribology
Presenter: A.A. Voevodin, Air Force Research Laboratory
Authors: A.A. Voevodin, Air Force Research Laboratory
J.G. Jones, Air Force Research Laboratory
T.C. Back, Air Force Research Laboratory
J.S. Zabinski, Air Force Research Laboratory
V.E. Strelnitzki, Kharkov Physical Technical Institute, Ukraine
I.I. Aksenov, Kharkov Physical Technical Institute, Ukraine
Correspondent: Click to Email
Unhydrogenated amorphous diamond-like carbon (DLC) and fullerene-like carbon nitride (CNx, N/C ratio ~ 0.2) are rival surface protection coatings with exceptional mechanical and tribological properties. A comparative study was performed on their benefits for sliding wear protection. The coatings were grown in the same deposition system, using similar substrates, surface preparation procedures, functionally graded interlayers (Ti-TiC-C), and top layer thicknesses. They were produced using pulsed laser deposition (PLD) and filtered cathodic arc deposition (FAD). Samples of laser-DLC, laser-CNx, arc-DLC, and arc-CNx coatings were prepared. Comparisons of coating chemistry, structure, hardness, elastic modulus, internal stress, coefficient of friction (c.o.f.) against steel and SiC balls, wear rate, and wear mechanism in humid and dry environments were performed. PLD and FAD provided very similar coating chemistry, structure and properties. Independent of the growth technique, DLC coatings had hardnesses within 52-57 GPa and elastic moduli within 490-560 GPa. The CNx coatings offered a reasonably high hardness of 28-30 GPa, while their elastic modulus was as low as 160 GPa. There was a clear difference in tribological behavior of DLC and CNx, which depends on the environment humidity. In humid air, DLC coatings had a c.o.f. of 0.1, a very low wear rate, and formed a graphitic transfer film in friction contact. In the same tests, CNx coatings had a c.o.f. of 0.3-0.4, a higher than DLC wear rate, and did not form a transfer film. In this environment, wear tracks on CNx coatings were polished by abrasion wear. In dry nitrogen, DLC coatings had a c.o.f. of about 0.15 and a higher wear rate, while CNx coatings had a c.o.f. 0.03-0.04 and a lower wear rate with formation of a graphitic-like transfer film. The observed difference in mechanical response and tribological performance can be used to optimize selection between DLC and CNx, depending on application requirements.