Structure of nanocrystalline WC-10%Co powder
(1. General Research Institute for Nonferrous Metals,
Beijing 100088, P.R.China；
2. Centre d'Etudes de Chimie Métallurgique/CNRS,
94407 Vitry-sur-Seine, France)
Beijing 100088, P.R.China；
2. Centre d'Etudes de Chimie Métallurgique/CNRS,
94407 Vitry-sur-Seine, France)
Abstract: Nanostructured WC-Co powders obtained by mechanical milling were investigated by combination of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) techniques. Rietveld analysis indicates that the experimental XRD patterns cannot be satisfactorily explained with the hexagonal WC structure. HRTEM image analysis shows that in the as-milled nanostructured powder, many WC grains contain stacking faults lying on the plane {10·0}. Analysis of phase images show that these defects are nearly periodically ordered along the ［10·0］direction. Based on these observations, a structural model was proposed for the WC grains with ordered stacking faults, which is in fact equivalent to a superstructure of WC with space group Amm2. When this model describing the faulted fraction of WC is introduced together with the normal WC structure (space group P 6￣m2) into the Rietveld refinement, a much better agreement between the calculated and experimental XRD profiles was obtained. This study allows to obtain the lattice parameters, grain size, microstrain and other structural information on the as-milled powders.
Key words: structural properties; mechanical milling; WC-Co