Quenching C60 fullerene into diamond in the Fe-C alloy system by laser treatment
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I.
INTRODUCTION
A S the hardest material known, diamond is an ideal candidate for mechanical application to superhard and wearresistant surfaces. The difficulty in growing a large-size single crystal of diamond turns attention to other aspects of research. Among those, the deposition of diamond films has attracted extensive interest and made great progress. Diamond films have now been successfully grown on various substrates by many methods, including chemical vapor deposition (enhanced by hot filamentt~.2.3]), RF plasma, t41 microwave plasma, t5,6,7] shock compression,iS] and detonation and combustion flames,tg,t~ However, the slow growth rate (ordinarily at microns per hourt~2]) and weak binding strength between the deposited films and substrates at the interface hinder their industrial application. This article describes diamond deposited by laser treatment in an Fe-C alloy system, providing an effective way to put this scientific curiosity into industrial reality. C60 fullerene, a newly discovered form of ordered carbon, t~3j is a spherical molecule containing 60 carbon atoms to form a closed hollow cage. t~41 The unique structure ensures its stability under hydrostatic compression at low pressure; C60 fullerene with fcc structure remained stable up to at least 20 GPa of hydrostatic compressiont151 and required nonhydrostatic compression to change its structure.tt6~ However, it is possible that ambient shear stress may trigger diffusionless transition from fullerenes to other forms of carbon, such as the martensitic transition suggested by Yamada and Sawaoka,t~7] when they found tiny spherical crystallites of distorted diamond in the detonation product. We treated C60/C70 coatings (self-produced) on 45# carbon steel with CO2 continuous laser output. Experiments were designed to fit the real level of factories condition. The CO2 laser was chosen because it is quite obtainable and widely used in factories. As for the substrate 45# car-
CHANGPING LI, Postdoctoral Candidate, formerly with the Department of Mechanical Engineering, Tsinghua University, is with Department of Material Science and Engineering, Iowa State University, Ames, IA 50013. BINGQING WEI, WENJIN LIU, JI LIANG, ZHIDONG GAO, and DEHAI WU, Professors, and JIHONG ZHANG, Postdoctoral Candidate, are with the Department of Mechanical Engineering, Tsinghua University, Beijing 100084, People's Republic of China. Manuscript submitted August 29, 1995. METALLURGICALAND MATERIALSTRANSACTIONSA
bon steel, its excellent combination of strength and toughness makes it widely usable in mechanical workpieces, such as shafts, gears, bars, piston rods, etc. In a word, the aim of this work is to bridge a gap between fullerenes and ordinary metals in industry. II.
EXPERIMENT
A. Starting Material The C60 fullerene was prepared by the KriitschmerHuffrnan method in a homemade reactor~lsl and extracted with benzene. Full characterizationE~91 showed that the C60/C70 mixture is the main part of the product, occupying about 85 pct by weight, and the ratio of C60 to C70 i
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