Protective coatings of nanophase diamond deposited directly on stainless steel substrates
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Protective coatings of nanophase diamond deposited directly on stainless steel substrates F. Davanloo, H. Park, and C. B. Collins Center for Quantum Electronics, University of Texas at Dallas, P.O. Box 830688, Richardson, Texas 75083-0688 (Received 27 December 1995; accepted 18 March 1996)
Composed of sp3 bonded nodules of carbon, nanophase diamond films are deposited in vacuum onto almost any substrate by condensing carbon ions carrying keV energies. These multiply charged ions are obtained from the laser ablation of graphite at intensities in excess of 1011 W cm22 . The high energy of condensation provides both the chemical bonding of such films to a wide variety of substrates and low values of residual compressive stress. Coatings of 2–5 mm thickness have extended lifetimes of materials such as Si, Ti, ZnS, ZnSe, and Ge against the erosive wear from high-speed particles by factors of tens to thousands. In this research emphasis has been placed on studies of the bonding and properties realized by the direct deposition of nanophase diamond films on stainless steel substrates. Examinations of interfacial layers showed deep penetrations of carbon atoms into steel substrates. Resistances to low and high impact wear estimated by a tumbler device and a modified sand blaster, respectively, and results indicated significant increases in the lifetime of stainless steel samples. The characterization studies in this work demonstrated nanophase diamond as an attractive material for use as a protective coating in current industrial applications.
I. INTRODUCTION
Nanophase diamond films have been produced by accelerating and quenching an intense laser plasma of C31 and C41 onto a cold substrate.1–8 Microstructural studies of nanophase diamond films have shown them to be composed of hard dense nodules with grain sizes on the order of 10 –50 nm. The diamond characteristics of this material have been evaluated by several analytical methods. Measurements agree in supporting sp3 contents of better than 75%.3–5 No other source has been reported for this material and, to date, the quenching of C1 ion beams onto a substrate has been shown to produce only i-C or defect graphite.4–7 The importance of this nanophase diamond material has been suggested by recent reports of its unique mechanical properties.5,6 It was shown that a combination of low internal stress and high bonding strength produced coatings with exceptional resistance to wear and erosion. Analyses of the interfaces of nanophase diamond film on several substrates showed significant interfacial layers.5,6 These were caused by the highly localized but intense levels of energy density created by impacts of C31 and C41 ions. Nanophase diamond seems to be a unique product of laser plasma processing. Original samples of this material were called amorphous ceramic diamond, an appellation contracted to “amorphic diamond” for convenience.1–7 However, the recent improvements have succeeded in bringing the hardness of such films above 80
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