Effect of composition on the streaking and diffuse intensity in decagonal phase in Al70-XCo15CuX+YNi15-Y system

We report here the transmission electron microscopic examination of alloys of three compositions in the system Al70-XCo15CuX+YNi15-Y. They have been c hosen on the basis of: (a) Ela ratio lying between Al65Co15Cu20 (ACC) and A l70Co15Ni15 (ACN) and (b) a possible observation of change in order from AC N to ACC, the end members. The selected area diffraction studies of the mel t-spun ribbons of the above compositions have revealed the presence of stre aking around some spots and also diffuse rows. These have led to the transf ormation of a basic P10(5)/mmc structure to that of P10/mmm having a period icity of similar to8 Angstrom. Such a transformation has been explained bas ed on the SD model earlier proposed by us. The chemical ordering in the lay ers is shown to accomplish the transformation. However, streaking arises ow ing to the presence of planar faults with a fault vector having periodic an d quasiperiodic components. (C) 2000 Elsevier Science B.V. All rights reser ved.