Nature of streaking and ordering in rapidly solidified Al–Co–Cu–Ni system

The two compositions Al70Co15Ni15 and Al65Cu20Co15 forming decagonal phases in both as-cast and rapid solidification conditions display subtle differences in their diffraction patterns. We present here the structural investigation of a series of alloys in Al–Co–Cu–Ni system under rapid solidification conditions. Many interesting structural features giving rise to subtle differences in the nature of streaking and also diffuse intensity will be discussed. An attempt will be made to correlate these effects with the chemistry of the alloy. The observation of diffuse intensity leading to the change in symmetry from P105/mcm to 10/mmm will be considered in terms of statistical occupancy of various components constituting the above systems.