Low-temperature internal friction in quenched niobium

Abstract

Internal friction measurements (at 1 cycle/sec) have been carried out over the temperature range from 100 to 280° K on niobium specimens quenched to room temperature from 2350° C. Internal friction curves immediately after quenching exhibited irregular peaks which were practically removed by a 20 h anneal at room temperature. On subsequent isochronal annealing three well-defined peaks occurred at about 185°, 200°, and 220° K. The relaxation strength of the peaks increased with increasing annealing temperature up to about 140° C, remained practically constant between 140° and 220° C, and subsequently gradually decreased to negligibly low values at about 380° C.

The variation of the damping spectrum, as a result of quenching and subsequent room temperature and isochronal annealing, indicates the presence of an excess of quenchedin vacancies in the material. Most of the vacancies are probably trapped at dislocations, at interstitial impurities or in clusters.

The 185, 200 and 220° K relaxation peaks developed by post-quench annealing have been identified asβ-peaks observed in cold-worked BCC transition metals. The relaxation mechanisms causing these peaks have been shown to be vacancy clusters, which may also involve interstitial impurities.