Single crystal PWA 1483 superalloy: Dislocation rearrangement and damping phenomena

The structural stability of the single-crystal PWA 1483 superalloy has been investigated by internal friction (IF) and dynamic modulus measurements from room temperature to 1073 K. The examined samples were in the solubilized state.The vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibrations has been employed. Frequency was ∼350 Hz.IF spectra recorded in successive test runs on the same samples show a Q−1 maximum (M1) above 623 K, whose intensity and position change from one run to another; in correspondence with M1 the modulus undergoes a slow decrease followed by a sudden increase. Sometimes another maximum (M2) has been observed at lower temperature (∼523 K).After each run the values of the modulus and of Q−1 change indicating that a progressive irreversible transformation occurs. Damping phenomena have been attributed to the rearrangement of dislocation structures in the disordered matrix. This rearrangement modifies the density and the average distance of pinning points. This explanation is supported by transmission electron microscopy (TEM) observations.