AVS 50th International Symposium
    Advanced Surface Engineering Tuesday Sessions
       Session SE-TuM

Invited Paper SE-TuM4
Self-adaptation Processes in Nanostructured Hard Coatings

Tuesday, November 4, 2003, 9:20 am, Room 323

Session: Nanostructured, Nanocomposite, and Functionally Gradient Coatings
Presenter: C. Mitterer, University of Leoben, Austria
Authors: C. Mitterer, University of Leoben, Austria
P.H. Mayrhofer, University of Leoben, Austria
E. Badisch, Materials Center Leoben, Austria
M. Stoiber, Materials Center Leoben, Austria
G. Gassner, Materials Center Leoben, Austria
Correspondent: Click to Email
Hard coatings deposited by plasma-assisted vapor deposition are widely applied to reduce tool wear. In the last decade, nanocomposite coatings have attracted increasing interest, due to the possible design of superhard coatings. Recently, it has been shown that nanostructured coatings also allow the realization of self-adaptive properties. This work summarizes recent developments in this field. The unavoidable Cl impurities in TiN coatings deposited by PACVD using TiCl@sub4@ as precursor is known to deteriorate mechanical coating properties when exceeding several at.-%. However, small and tolerable Cl concentrations of about 3 at.-% cause a reduction of the friction coefficient against various steels and alumina from 0.8 to 0.15. This is due to the formation of an interfacial lubricant film on top of the coating caused by Cl-stimulated rutile formation in humid air. These coatings have been shown to improve the lifetime of metal forming tools significantly. Low-friction behavior at elevated temperatures, which is a pre-requisite for dry cutting operations, can be achieved by liquid oxide lubrication. This can be realized by various nitride phases, e.g. VN, WN, Mo@sub2@N or MoN, which form low-melting oxides in the temperature range between 400 and 550°C. Melting of these phases occurs between 650 and 850°C. Using a nanoscaled arrangement of these phases in a hard matrix results in a self-adaptation of the friction coefficient to values of 0.18-0.4 at 700°C. Self-hardening to increase the wear resistance can be observed in metastable (Ti,Al)N coatings due to spinodal decomposition into fcc TiN and AlN domains. These nanoscaled coherent domains introduce additional stresses into the coating resulting in a hardness increase in the temperature range between 600 and 1000°C. These nanoscale design approaches allow the utilization of functional properties facilitating the development of next generations hard coatings.