MECHANICAL LOSS SPECTRUM OF NI-3(AL, TA) SINGLE-CRYSTALS

Mechanical loss measurements were performed by means of torsion pendul a on polycrystalline and single crystalline specimens of a Ni-3(Al,1%T a) alloy with the Ll(2) ordered structure. Measured internal friction spectra are characterized by the occurrence of two main phenomena: a w ell-defined internal friction peak at a temperature of similar to 950 K, for a frequency of 1 Hz and an internal friction background, which exponentially increases at higher temperatures. The internal friction peak with an activation energy of 2.97 +/- 0.1 eV was interpreted as a point defect relaxation peak induced by the presence of Al-Al elastic dipoles on octahedral planes, while the internal friction background was found to well reflect the decreasing (resp. increasing) mobility o f superdislocations on the primary octahedral (resp. cube) planes belo w (resp. above) the peak temperature in flow stress. (C) 1997 Elsevier Science S.A.