High Temperature Mechanical Spectroscopy in Ordered Ni₃(Al, Ta)

Abstract

Mechanical loss measurements were performed on polycrystalline and single crystalline samples (of three different orientations) of a Nij(Al,l%Ta) alloy with the L12 ordered structure. Measurements were conducted in torsion pendula, on as-cast samples and samples predeformed either at 300 K or at 1300 K, and revealed the occurrence of two main phenomena: (a) The presence of a well-defined internal friction peak at a temperature of about 950 K for a frequency of 1 Hz. This relaxation peak has an activation energy of about 3 eV and its amplitude is strongly dependent on sample orientation and predeformation conditions. (b) An internal friction background, which amplitude at high temperatures (above 1100 K) mainly depends on strain amplitude and predeformation conditions. Both phenomena appear closely related to the presence of point defects, to the complex dissociation mode of s~erdislocations and to the change in dislocation mechanisms occurring at the peak temperature in flow stress (about 800 K) in relationship with a change in active slip systems.

Single crystal PWA 1483 superalloy: Dislocation rearrangement and damping phenomena

“…A peak with H and 0 close to those of peak 1 [2] has been observed by other investigators [1,3,4] who have given alternative interpretations. The peak was attributed by Gadaud et al [1] to Ni diffusion whereas Mourisco et al [3,4] considered it as a Zener peak.…”

“…The peak was attributed by Gadaud et al [1] to Ni diffusion whereas Mourisco et al [3,4] considered it as a Zener peak.…”

“…From the comparison of H values of the two peaks with the diffusion energies of Ni and Al obtained in a Ni 3 Al singlecrystal by the diffusion experiments of Frank et al [9], peak 2 was attributed to the diffusion of Ni in the sub-lattice of Ni sites. Peak 1, with higher activation enthalpy, was ascribed to the diffusion of Al atoms which jump into the nearest neighboring sites of Ni forming anti-site defects.…”

Probing diffusional jumps in ordered compounds by anelastic relaxation spectroscopy

“…Detailed experiments have been carried out on one of such effects: the relaxation effect in Ni 3 Al, which was interpreted to be due to stress-induced reorientation of antisite Al atoms in the Ni-sublattice (Numakura et al 1999), focussing on the effects of deviation of composition from stoichiometry. The relaxation strength has been found to increase sensitively with increasing Al concentration, supporting firmly the earlier interpretation.…”

“…The relaxation strength has been found to increase sensitively with increasing Al concentration, supporting firmly the earlier interpretation. The observed relaxation rates have been analysed on the basis of the mechanism of atomic diffusion ) to evaluate the diffusion coefficient of Al in Ni 3 Al for various compositions.…”