Investigation of the mechanical and structural properties of Ti-Hf-C-N arePVD coatings

Nowadays, a few coating systems are commercially available (TiN, TiCN, CrN, TiAlN, WC/C, ADLC). These coating systems are used for various application s, In the range of cutting procedures, TiN-coated tools are widespread. Fur ther developments have led to coatings based on the systems Ti-C-N and Ti-A l-N possessing improved properties. In interrupted cut machining, for examp le, the lifetime of Ti-C-N-coated cemented carbides is four times higher th an that of TiN-coated ones (O. Knotek, F. Loffler, G. Kramer. Vacuum 43 (5- 7) (1992) 645-648). This is a result of the favorable thermophysical and tr ibological properties of Ti-C-N (O. Knotek, E. Lugscheider, F. Loffler, G. Kramer. H. Zimmermann, Surf. Coat. Technol., 68-69 (1994) 489-493; E. Lugsc heider, O. Knotek, H. Zimmermann, in T.S. Srivatsan, J.J. Moore (eds.), Pro cessing and Fabrication of Advanced Materials IV, TMS Warrendale, PA, 1996) . The high hardness of TIC is the reason for the excellent low flank wear. TIN possesses higher formation enthalpies than TIC and therefore a batter r esistance to crater wear. The binary combinations of HM and HfC possess sim ilar properties to TIN and TiC, but their thermal stability is better. Thus HM and HfC possess higher melting points than TiN and TiC, respectively (R . Keiffer, F. Benesovsky, Hartstoffe, Springer, Vienna, 1963; W. Konig, Fer tigungsverfahren, Band 1, 4. Auflage, VDI. Dusseldorf, 1990). Because of th is, the substitution of Ti atoms by Hf atoms can be expected to lead to an improvement of wear behavior. First coatings from the system Ti-Hf-N were deposited with the are PVD proc ess. Based on these investigations, coatings in the quaternary system Ti-Hf -C-N were developed. Beside the number of layers (Ti-Hf-N/Ti-Hf-C-N), the c omposition of the reactive gas comprising nitrogen and the carbon carrier g as ethane was varied. During deposition with a high carbon carrier gas flow share (total pressure=constant), the coatings chipped off. Lower shares of carbon carrier gas, e.g. C2H6:N-2 = 1:4, led to smooth and dense coatings with good mechanical properties. With regard to different number of layers, the values of microhardness were around 2900 HV 0.05. (C) 1999 Elsevier Sc ience S.A. All rights reserved.