Phase transformations of NbCr2 intermetallics produced by mechanical alloying followed by hot-pressing consolidation

Mechanical alloying followed by hot-pressing consolidation has been used to produce NbCr2 intermetallics under different conditions. High-purity Nb and Cr crystalline powders, in the relative (molar) ratio of 13:1, were milled for periods up to 100 h. This powder was vacuum-sintered at temperatures ranging from 1423 to 1573 K for 0.5 h under a pressure of 45 MPa, The phase transformations of the NbCr2 were investigated by X-ray diffraction and scanning electron microscopy; several different phase transformations were observed. Increasing the milling time up to 100 h transforms into a mixture of C14, Nb, Cr and C15. The experimental results show that new evidence based on X-ray diffraction measurements further establishes the existence of a high-temperature C14 Laves polytype; an intermediate C36 structure for NbCr2, reported in the literature, was not detected in this study. The relationship between the various phase transformations, based on the atomic radii and different preparation techniques, is discussed. (C) 2007 Elsevier Inc. All rights reserved.