Crystallite size and lattice strain determination of NiAl-Al2O3 nanocomposite from x-ray diffraction line broadening
Dariusz Oleszak, Andrzej Olszyna Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa
Annals 4 No. 11, 2004 pages 284-287
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abstract Nanostructured materials are intensively studied due to their good properties, in many cases better than properties of their conventional polycrystalline counterparts, exhibiting micrometer-range grains. Nanocrystalline materials are fabricated by different techniques, including mechanical alloying or reactive milling. The resulting powders usually have particle size of several micrometers, but they consist of nanometric crystallites. X-ray diffraction seems to be a simple technique for determination of crystallite size and lattice strain from the broadening of the diffraction lines. The aim of this work was to determine crystallite size and lattice strain of nickel aluminide and alumina. Both phases were formed during reactive milling of NiO+Al powder mixture. The average crystallite size and lattice strain were calculated from X-ray line broadening, applying different profiles of diffraction lines. The first method assumes that diffraction line broadening from microstructure refinement and that arising from strain are both described by Cauchy function. This approach is known as Williamson-Hall method. In the second method both contributions are of Gauss type. Finally, the last one asumes that size-broadening is Cauchy type, while strain induced broadening is Gaussian. The obtained values of crystallite size and lattice strain for alumina were in the range 27÷58 nm and 0.3÷0.48%, respectively, depending on the method of calculation. For all methods the correlation coefficient of fitting was reasonable. In the case of NiAl the calculated values of crystallite size and lattice strain were in the range 13÷29 nm and 0.29÷0.77%, respectively, depending on the calculation method. However, significant scattering of experimental data was observed due to the anisotropy of this compound. As a consequence, the fitting parameters were rather poor. Key words: X-ray diffraction, crystallite size, lattice strain, nanocomposites, NiAl, alumina