Synthesis of diamond films on Hastelloy
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We have developed a two-step hot filament chemical vapor deposition method to form polycrystalline films of diamond on Hastelloy substrates. The first step at a lower temperature results in the deposition of a composite layer of carbon, diamond-like carbon, and diamond, which provide nucleation sites for diamond growth in the second step at a higher temperature. To obtain a cleaner amorphous carbon-free diamond film, we introduced an intermediate hydrogen etching step. Using this procedure, we have obtained high quality polycrystalline diamond film on Hastelloy substrates, as characterized by scanning electron microscopy and Raman measurements.
I. INTRODUCTION Diamond films have been deposited on various elemental as well as alloy substrates such as silicon (Si), copper (Cu), silicon carbide (SiC), silicon oxide (SiO2), and tungsten carbide (WC) using the hot filament chemical vapor deposition (HFCVD) method.1^5 The extent of diamond nucleation, in many cases, is found to be related to the carbide-forming ability of the substrate material. Abrading the substrate surface with submicron size diamond grit is also known to enhance diamond nucleation in many cases, wherein it is established that polishing residues provide nucleation sites for the diamond phase.6'7 However, in the context of deposition of diamond film on some other types of substrates such as iron and its alloys and Hastelloy, many difficulties are encountered, particularly those related to the high diffusivity of carbon into the substrate. It is also found that diamond and diamond-like residues introduced via scratching/abrasion by diamond grit are unstable on iron and iron alloys above a typical deposition temperature —800 °C, and as such are ineffective in providing nuclei for diamond growth. Recently, we have investigated the use of laser treatment for enhancing nucleation and adhesion of diamond films on various substrates.8 In this paper, we report a two-step deposition method using HFCVD to form diamond film on Hastelloy, which is a nickel-based superalloy9'10 containing chromium (16%), molybdenum (17%), and iron (6%) as major alloying elements. Due to its high mechanical strength and excellent corrosion resistance at elevated temperatures, Hastelloy is a technologically very important material having applications10 ranging from aircraft gas turbines to metal processing. Since diamond exhibits a
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'On leave from Department of Physics, University of Poona, Pune 411007, India. J. Mater. Res., Vol. 7, No. 10, Oct 1992
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high degree of hardness, corrosion resistance, and also biocompatibility with human body tissues, its coating is expected to enhance many applications as mentioned above, including medical applications of prosthesis components. The two-step method basically involves HFCVD initially at lower temperature (—700 °C), which leads to formation of diamond-like carbon and diamond residue. This is followed by a deposition at higher temperatures to form diamond film. An intermediate step
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