An investigation on the transformation of the decagonal phase to a B2 phase in Al-Cu-Co alloy during mechanical milling

Al65Cu20Co15 decagonal phase, synthesized by a slow cooling technique, were mechanically milled in a high energy planetary ball mill for 10, 20 and 30 h. X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques were used for characterization of phases. The phase transformation from the decagonal phase to a B2-crystalline phase (ordered CsCl type phase) during mechanical milling is reported here for the first time. Powders milled for more than 10 It contained predominantly the B2 type crystalline phase with a lattice parameter of 0.29 nm. This crystalline phase was found to be quite stable after 30 h of milling and also on subsequent annealing at 600 degreesC. These experimental results lend support to an earlier suggestion that the decagonal phase in Al-Cu-Co is actually less stable than the B2 phase at low temperatures. (C) 2002 Elsevier Science B.V. All rights reserved