X-RAY AND ELECTRON-DIFFRACTION INVESTIGATIONS ON THE STABLE DECAGONAL PHASE IN CO-NI-AL ALLOYS

The stable decagonal phase in alloys with compositions of Co15Ni15Al70, Co11.5Ni16Al72.5, Co16.5Ni11Al72.5 and Co2ONi7.5Al72.5 was investigated by X-ray and electron diffraction. All important projections of the reciprocal lattice of the decagonal phase were obtained by electron diffraction. The tilt angles between the individual zone axes were measured and compared with calculated angles. From the diffraction patterns the reciprocal lattice could be reconstructed. A simple method for the indexing of the reciprocal lattice is introduced. The indexing scheme is based on five linearly independent vectors. The indices for the reflections in the electron diffraction as well as the X-ray powder diffraction patterns are tabulated. The indices of the zone axes studied by electron diffraction could also be determined. In the X-ray diffraction studies a substantial variation of the number and of the position of the diffraction lines with alloy composition was found. The results are compared with results from the stable decagonal phase in the system Co - Cu - Al.