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.