Patterning of Hard Coatings for Incorporation of Solid Lubricant Microreservoirs
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Patterning of Hard Coatings for Incorporation of Solid Lubricant Microreservoirs Canan G Guleryuz, and James Krzanowski Mechanical Engineering, University of New Hampshire, 33 College Rd., Durham, NH, 03824 ABSTRACT Hard coatings containing microscopic reservoirs for solid lubricant storage have the potential to advance the development of dry, self-lubricating coatings. In the present study we have investigated several methods for fabricating hard coatings that incorporate microscopic reservoirs. These methods all involve the use of placeholders on the substrate surface that are later removed after deposition of the hard coating. One method uses a solution containing ceramic beads, while the second method uses conventional photolithography methods. Coatings using both of these methods were fabricated using TiN as the hard coating. The effectiveness of the microreservoirs for solid lubricant storage was examined by conducting pin-on-disk test using various solid lubricants, including graphite and indium. The performance of coatings with random arrangements of microreservoirs was scattered while samples with the ordered arrangements of microreservoirs all performed well. Optical microscopy examination of the wear tracks showed the microreservoirs were generally successful at trapping the graphite lubricant during wear. With a sufficient density and appropriate distribution of the microreservoirs, the significant improvements in tribological performance can be realized. INTRODUCTION The tribological coatings area has observed steady advances for the last several decades. Because of the limited ability of single layer/single phase coatings in arresting cracks, controlling residual stress, adhesion, carrying high-level loads, multilayered/multiphase, gradient, superlattice, nanostructured, and composite coatings have been investigated [1,2]. Endrino et.al. examined magnetron sputter-deposited coatings of carbides (WC and TiC) together with Ag to create a composite providing good wear life and solid lubrication. Separate carbide and Ag phases were obtained, and in a vacuum environment, friction coefficients were reduced compared to carbide coating alone case. There was also an optimum Ag content that provided the lowest friction coefficient for these conditions [3]. Voevodin et.al. [2] studied three-dimensional structuring of tribological coatings by IR laser technology. First a gradient Ti-TiC-TiC/DLC coating was deposited on steel substrates. This coating was designed to have enough load carrying capacity, good adhesion and to provide stress relaxation. Secondly, a groove was created in the coating using a laser, and MoS2 was deposited into this groove and on the whole surface. Ball-on-disk wear tests showed wear life of this coating architecture was at least two orders of magnitude higher than a MoS2 film on steel or on gradient film. Also, this structure
showed environmental adaptivity to dry and humid air environments. In a recent study [4] Voevodin and Zabinski created three dimensional reservoirs in
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