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Elastic constants relate technological, structural and safety aspects to various materials phenomena and to their fundamental interatomic forces. Hence, they are of fundamental importance in almost all engineering applications. Thus its determination is of utmost importance. The aim of the present investigation is to study the behaviour of elastic constants and the variation on heat treatment in a nickel base super alloy Nimonic 263 by ultrasonic velocity measurements. From the present study it is evident that the elastic moduli of the material are very sensitive to any minor compositional changes, resulting due to the formation of intermetallic phases on heat treatment and can be effectively monitored by ultrasonic.

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Samples of a decagonal quasicrystalline phase, located in the Al±Cu±Co system and synthesized by a slow cooling technique, have been mechanically milled in a high-energy planetary ball mill for 10, 20 and 30 h. The milled powders, as well as powders that had been annealed (after milling) for times ranging from 30 to 150 min at 600°C, were characterized by X-ray di raction, scanning electron microscopy and transmission electron microscopy. A phase transformation from the decagonal phase to a B2 crystalline phase during highenergy ball milling is reported here for the ®rst time. Powders milled for more than 10 h 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 milling for 30 h and also on subsequent annealing at 600°C. 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.

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