Internal-friction study of solute segregation to dislocations

Internal Friction (IF) techniques operating at a frequency of 1.3 kHz were used to measure the solution hardening component of the flow stress as a function of temperature, static aging time, and solute concentration in single crystal alloys of Al-Mg and Cu-A1. During the IF tests most of the dislocations remained in their aged condition. A small fraction of the dislocation density was set free from their solute cloud by the application of a sufficiently large periodic stress. The kinetics of solute segregation to the freed dislocations was then monitored with the IF method. The experimental results were interpreted in terms of recent computer-modeling calculations for IF losses in random alloys. The kinetics of solute segregation shows three regimes. At low temperatures the dislocations interact with a fixed population of solutes. At intermediate temperatures solutes segregate to stationary dislocations mostly from the region surrounding the dislocation cores, without the assistance of an excess concentration of vacancies generated by plastic deformation. At high temperatures the segregation reaches a saturation value because the solutes tend to remain in solution, rather than segregate to dislocations.