AVS 46th International Symposium
    Vacuum Metallurgy Division Wednesday Sessions
       Session VM-WeM

Paper VM-WeM4
Tribological Performance and Initial Finite Element Modeling of Reactively Sputtered Single and Multi-layer Chromium Nitride Thin Films

Wednesday, October 27, 1999, 9:20 am, Room 620

Session: Advanced Surface Treatments and Coatings
Presenter: S.L. Rohde, University of Nebraska, Lincoln
Authors: S.L. Rohde, University of Nebraska, Lincoln
D. Mihut, University of Nebraska, Lincoln
S. Kirkpatrick, University of Nebraska, Lincoln
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This work examines the tribological properties of CrN and Cr@sub 2@N thin films both as single-layers and in a number of different multilayer structures combining CrN, Cr@sub 2@N and Cr. The overall program goal was to test the feasibility of "building-in" load support, by alternating hard/soft film layers to optimize performance on hard materials, such as hardened tools steels, as well on compliant materials like Al-alloys. The first phase of this program centers on the deposition and evaluation of an array of coating structures on various substrates. Thin films were deposited in a mixed Ar-N@sub 2@ discharge, using a single unbalanced magnetron cathode with a Cr-target operating in a metallic-mode. Three differing substrate materials were coated; 52100 bearing steel, A2 tool steel and 2024-alloy aluminum. The adhesion of the thin film/substrate couples was evaluated using scratch adhesion and Rockwell C indentation testing. Scratch adhesion values were found to range from 2 to 8 kg depending on the hardness of the substrate material; with the lowest values occurring on the most compliant substrates (i.e. 2024 Al). The wear behavior was assessed using pin-on-disk and high frequency Cameron-Plint testing. The pin-on-disk tests were performed without additional lubrication at 40 to 50% humidity using alumina and/or tungsten carbide balls as the pin materials. . The wear was reduced in most cases, with the multi-layered structures performing best on all substrate materials. The lubricated Cameron-Plint tests run on coated 52100 steel substrates favored the Cr@sub 2@N-based films, although the hardness of these multilayers is frequently lower than the corresponding CrN-based structures. While on the A2 tool steel substrates, the hardest thin film structures yielded the best PoD wear performance, these same films did not perform as well on the more compliant Al-substrates. For the Al-substrates, neither the stiffest nor the most compliant films excelled, instead multi-layer film with alternating hard/soft structures designed to provide a more graded compliance from the substrate up to the rigid top layer yielded the best results. In this case, wear rates were reduced by as much as much as three orders of magnitudes over uncoated 2024 Al. Finite element modeling studies have been initiated to try to understand the behavior of these multilayered coating/substrate combinations under specific loading conditions. While still in it's earliest stages, the ultimate goal of the modeling program will be to facilitate design and optimization of application specific coating structures into the original component design stage. To accomplish this models are being developed for previously tested film structures on various substrates, and these models will then be used to guide the development of second generation coatings, that will be used to verify and improve the efficacy of the models.