Preparation and Mechanical Properties of Nanostructured Tungsten Carbide Alloys Strengthened by Carbon Nanotubes
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L8.41.1
Preparation and Mechanical Properties of Nanostructured Tungsten Carbide Alloys Strengthened by Carbon Nanotubes 1)
G. L. Tan1), X. J. Wu2), Z. Q. Li2) Department of Materials Science & Engineering, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA19104 2) Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China ABSTRACT
A novel approach for the synthesis of carbon nanotubes strengthened nanostructured tungsten carbide was investigated, in which nanophase tungsten powders are carburized by C2H2 instead of CO and a fraction of decomposed carbons were in situ converted to nanotubes. In this way, the composite powders of nanocrystal WC-Co and carbon nanotubes have been in situ prepared. The composite WC-Co powders were then hot pressed into bulk alloy which shows a exceptionally high microhardness up to 3307 kg/mm2. It is proposed that carbon nanotubes with extra high Young’s modulus (1.8 Tpa) play both roles on strengthening the composite matrix and prohibiting growth of WC grains, which results in the great improvement of the mechanical properties of the samples. The average grain size of the prepared WC-Co hard alloys was estimated to be less than 100 nm. The effect of hot press temperature on the mechanical properties of the prepared alloys was also studied in detail.
1. Introduction Carbon nanotubes are predicted to have interesting mechanical properties, in particular, high stiffness and axial strength, as a result of their seamless cylindrical graphite structure [15]. The Young's modulus of the carbon nanotubes is measured by M.M.J.Treacy to be as exceptionally high as 1.8 TPa [6]. Meanwhile, nanostructured WC-Co alloys exhibited much higher microhardness than the conventional counterpart with coarse grains [7]. WC-Co alloy is a kind of widely used engineering material. It is well known for a long time that the finer crystalline microstructure is favor to its mechanical properties. Although a lot of efforts have been made to improve the alloy properties, their microhardness still keeps at a level of 1700 kg/mm2 and little progress was achieved in this aspect. It was until 1989 that L. E. McCandlish [9] created a new chemical process, called spray-fluid bed conversion, with which he successfully synthesized homogenous nanophase WC-Co powders. These powders were sintered at a temperature of 1300°C, the sintered hard alloys shown a high microhardness up to 2260 kg/mm2. That was a great progress for the WC-Co hard alloys, but it is very difficulty to make more advances because of the intrinsic characteristics of WC-Co hard alloys and the rapid growth of the grain size during the sintering. Under this consideration, we propose a novel approach to synthesize the composite materials of nanostructured WC-Co and carbon nanotubes, which greatly break the limit of mechanical properties for the pure nanostructured WC-Co alloys through the reinforcement of carbon nanotubes. In this new process, nanophase tungsten powders are carburized by C2H2 instead of CO and a fr
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