Polytypism in alloys

Abstract This paper summarizes polytypes in alloys having layer structures such as Laves phases and Sm-Ni intermetallics which were studied by X-ray diffraction and electron microscopy. In the Mg-base pseudo-binary Laves phases, many stacking variants were found as a function of electron concentration. They are 4H, 6H, 3C, 4H, 21R, 10H, 16H, 9R, 6H', 14H, 8H and 2H in order of increasing e/a from 0.67 to 2.0. Many polytypes were also observed in the specimens of Sm2Ni7 and Sm5Ni19 compounds. Polytypes found in Sm2Ni7 are 2H, 3R, 4H, 5T, 9R, 12R, and for Sm5Ni19 2H, 3R, 4H, 5T, 6H, 7T, 9R, 12R, 15R, 18R were recognized. Stacking faults, intergrowth and many defect structures were observed under the electron microscope.