X-ray studies on NiAl-Cr3C2-Al2O3 composite powder with nanocrystalline NiAl phase

The X-ray diffraction studies were performed on NiAl-Cr3C2-Al2O3, composite powder prepared by self-propagating high-temperature synthesis (SHS) method. As-prepared powder was milled by attritory mill for up to 10 h. The Rietveld method was applied for the analysis of whole diffraction patterns whereas the Toraya procedure was useful for the profile analysis of the individual diffraction lines. The contents of NiAl, Cr3C2 and Al2O3 phases were found to be 78.8, 13.9 and 7.3 wt.%, respectively. From the detailed analysis of the width of diffraction lines for all phases it was stated that during milling the significant decrease of crystallite size is observed only for NiAl phase. Moreover it was found that the crystallite size of this phase diminishes to nanoscale after 2 h milling. Prolonged milling time to 10 h results in further decrease of NiAl crystallite size to 36 nm. The crystallite size of Cr3C2 and Al2O3 phases is still above 100 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the sample milled for 10 h show that the size of the agglomerates of NiAl nanocrystallites changes in a broad range and that Cr3C2 and Al2O3 particles can be immersed in larger agglomerates or occur separately.