Snoek relaxation and ultrasonic shear-wave attenuation were studied in steels which contained 1.29at%Cu and were subjected to various isothermal aging treatments. The hardness increased with aging time and, after reaching a maximum, then decreased. The peak hardness was 17% higher than that of non-aged material. Aging embrittlement was caused by body-centered cubic Cu clusters which precipitated from the ferrite Fe crystal. By using a forced-vibration torsion-pendulum method, a study was made of the aging

 effect upon the internal friction spectrum (peak position and strength) and decay of the maximum internal friction after quenching from 723K. A broad asymmetrical peak was observed which was centered near to 0.1Hz at room temperature. It could be decomposed into 3 Debye peaks. The decay rate exhibited a correlation with hardness, in that a faster decay occurred in the harder steel. A monotonic decrease in ultrasonic attenuation was observed after quenching; thus indicating the diffusion of C atoms to dislocations. The Snoek relaxation results were explained in terms of the Nowick theory of interstitial/substitutional solute interactions. The Granato-Hikata-Lücke theory, and the Cottrell-Bilby t2/3 model, were used to analyze the decay measurements. They explained the measurements well and permitted an estimation to be made of the evolution of dislocation density with aging. The transmission electron microscopic observations supported these conclusions.

H.Ogi, H.Ledbetter, S.Kim: Snoek Relaxation and Dislocation Damping in Aged Fe-Cu-Ni Steel. Metallurgical and Materials Transactions A, 2001, 32[7], 1671-7