Mechanical loss spectrum of Ni3(Al, Ta) single crystals

Mechanical loss measurements were performed by means of torsion pendula on polycrystalline and single crystalline specimens of a Ni-3(Al,1%Ta) alloy with the Ll(2) ordered structure. Measured internal friction spectra are characterized by the occurrence of two main phenomena: a well-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 of superdislocations on the primary octahedral (resp. cube) planes below (resp. above) the peak temperature in flow stress. (C) 1997 Elsevier Science S.A.