Tribomechanical Properties of Ion-Beam-Densified Sol-Gel Zirconia Thin Films on Cubic Zirconia
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TRIBOMECHANICAL PROPERTIES OF ION-BEAM-DENSIFIED SOLGEL ZIRCONIA THIN FILMS ON CUBIC ZIRCONIA Timothy E. Levine, Peter Revesz, James W. Mayer, and Emmanuel P. Giannelis Cornell University, Department of Materials Science and Engineering, Ithaca, NY 14853 *Presently at Arizona State University, Tempe, AZ 85278-1804
ABSTRACT We have investigated the tribomechanical properties of ion-beam-densified sol-gel zirconia overlayers on bulk zirconia. Ion irradiation of the sol-gel films leads to hydrogen, oxygen, and carbon losses as indicated by Rutherford backscattering spectrometry and forward recoil energy spectroscopy. Ellipsometry measurements show that the film thickness decreases with increasing dose. The microhardness exhibits an increase and subsequent decrease with dose. Friction measurements along with profilometry measurements indicate that severe abrasive wear of the film takes place in the first 1000 cycles after which point the substrate is in direct contact with the pin.
INTRODUCTION Fully stabilized cubic zirconia (FSZ) is a technologically important structural ceramic because of its high strength, corrosion resistance, and refractory nature. However under some loading conditions FSZ exhibits brittle behavior. Furthermore many potential mechanical applications of FSZ make fluid lubrication impossible, thus creating the potential for excessive wear of mating surfaces. The optimum tribostucture consists of a fracture tough substrate and a lubricious surface that together would endure impact loads and yield minimum wear of mating surfaces.
Fleischer et al. attempted to create such a structure through an ion implantation process where the near-surface is amorphized via a lower energy implant and a deeper region is toughened by a more energetic implant. Their efforts to amorphize the near-surface of FSZ via implantation of various species and energies yielded a highly damaged yet crystalline structure [1]. In another study, investigations of excimer laser processed metal films on FSZ improved the wear properties but reduced thenear-surface hardness [2].
In this paper we present the results of an investigation in which an amorphous overlayer is
deposited via sol-gel methods onto single crystal FSZ substrates and subsequently implanted with inert gas ions. We have shown previously that the sol-gel zirconia films deposited on silicon densify under the action of an inert gas ion beam [3]. Electron diffraction of the implanted films has shown that the films retain their amorphous character. In this scheme the implanted substrate can provide fracture toughness and the amorphous overlayer can provide a lubricious wear surface. Ion implantation of noble gas ions into FSZ has been shown to simultaneously increase hardness, reduce wear, and lower the sliding friction coefficient [4]. The microhardness varies with the total damage energy (TDE), which is simply the number of vacancies produced per incident ion times the dose times the energy of each ion. The effects of implantation of several species at various energie
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