Influence of sintering temperature and pressure on crystallite size and lattice defect structure in nanocrystalline SiC
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. Nauyoks Department of Physics and Astronomy, Texas Christian University, Fort Worth, TX 76129
L. Balogh Department of Materials Physics, Eötvös Loránd University, H-1518 Budapest, Hungary
J. Labar Department of Materials Physics, Eötvös Loránd University, H-1518 Budapest, Hungary; and Research Institute for Technical Physics and Materials Science, H-1525 Budapest, Hungary
T.W. Zerdaa) Department of Physics and Astronomy, Texas Christian University, Fort Worth, TX 76129
T. Ungár Department of Materials Physics, Eötvös Loránd University, H-1518 Budapest, Hungary (Received 20 September 2006; accepted 19 January 2007)
Microstructure of sintered nanocrystalline SiC is studied by x-ray line profile analysis and transmission electron microscopy. The lattice defect structure and the crystallite size are determined as a function of pressure between 2 and 5.5 GPa for different sintering temperatures in the range from 1400 to 1800 °C. At a constant sintering temperature, the increase of pressure promotes crystallite growth. At 1800 °C when the pressure reaches 8 GPa, the increase of the crystallite size is impeded. The grain growth during sintering is accompanied by a decrease in the population of planar faults and an increase in the density of dislocations. A critical crystallite size above which dislocations are more abundant than planar defects is suggested.
I. INTRODUCTION
Silicon carbide is frequently used as a functional and structural material at high temperatures. Nanocrystalline SiC (nc-SiC), offers very high strength in structural applications even at high temperatures.1 For this reason, silicon carbide often serves as a binding phase in composites, for example in diamond composites. Improvements in mechanical properties of SiC resulting from grain size reduction are expected.2,3 To modify the grain size of bulk SiC sintered from nanopowders, we varied the manufacturing pressure and temperature. It is expected that the microstructure of sintered SiC can be tailored by the proper selection of these two parameters.4 The influence of defects on mechanical properties of ceramics has been thoroughly investigated experimentally,5 but no theoretical model describing the relationship between deformations in the lattice, hardness, and a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0162 1314 J. Mater. Res., Vol. 22, No. 5, May 2007 http://journals.cambridge.org Downloaded: 09 Feb 2015
grain size dependence exists. The lattice defect structure in microcrystalline SiC has been studied by microscopic and x-ray diffraction (XRD) methods.6,7 The appearance of planar faults in SiC has been reported, and the density of these defects were estimated by comparing intensities of different x-ray reflections.6,8 However, results of that procedure become uncertain when other lattice defects, such as dislocations, are abundant and the microstructure consists of nanograins. Recently, the convolutional multiple whole profile (CMWP) fitting procedure9 worked out for the determination of cry
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