Heating-induced transformations of multicomponent alloys prepared by mechanochemical synthesis

Multicomponent (Cr, Fe, Co, Ni, Al, Ti, and Nb) powder alloys prepared by milling five- to seven-component equiatomic mixtures of elemental powders in a Fritsch (P-7) planetary mill have been characterized by differential thermal analysis and X-ray diffraction. The results demonstrate that, if the starting mixture contains Al, the BCC solid solution formed as a result of the milling undergoes heating-induced CsCl-type ordering (β-phase). If not only Al but also Ti are present in the starting mixture, further heating causes the β-phase to convert to an L21 phase with the composition (Ni,Co)TiAl. The elements Cr and Fe form a tetragonal σ-phase. The presence of Nb in the starting mixture suppresses the formation of the σ- phase and favors the formation of a hexagonal Laves phase of complex composition: (Fe,Co)CrNb.