DC-MSIP/HPPMS (Cr,Al,V)N and (Cr,Al,W)N thin films for high-temperature friction reduction

The application of high-strength steel and aluminum alloys entails increasing demands on the surfaces of tools used for forming processes. A promising approach towards the reduction of friction forces and thus towards the wear of tools is the application of self-lubricating coatings. Due to the high number of crystallographic shear planes and a partially low melting temperature, the so-called Magneli-phases offer excellent possibilities for the reduction of friction in tools at application temperatures between 600 degrees C and 800 degrees C. In order to achieve the aforementioned gliding planes vanadium (V) and tungsten (W) containing (Cr,Al)N thin films deposited via a combination of Magnetron Sputter Ion Plating (MSIP) and High Power Pulse Magnetron Sputtering (HPPMS) Physical Vapor Deposition (PVD) were activated in a high-temperature environment. In this context, the (Cr,Al)N matrix provides for wear protection while vanadium and tungsten are developing friction-reducing oxides under temperature influence. Hence, a diffusion of these metals to the surface during application is necessary for a continuous generation of dry or liquid lubricants. Within this paper a scanning electron microscope (SEM) was used for the analysis of the cross-section fractures of the coatings in order to allow statements about the coatings' morphology and thickness; further, annealing tests in an atmosphere furnace at 600 degrees C, 800 degrees C and 1000 degrees C were carried out. X-ray diffractometry (XRD) served for documentation of phase transformations. With an electron probe micro analysis (EPMA) the diffusion of elements was observed. To investigate the friction reduction high-temperature pin-on-disk (PoD) tribometer measurements (room temperature (RT), 600 degrees C and 800 degrees C) using a 100Cr6 counterpart were, moreover, carried out in atmosphere. Within these investigations we could show a reduction in the friction coefficient from 0.6 at room temperature to 0.05 at 800 degrees C for the (Cr,Al,V)N coating. Furthermore, a diffusion of V to the surface of the coating was demonstrated. However, a positive effect by using (Cr,Al,W)N cannot be verified. (C) 2010 Elsevier B.V. All rights reserved.