Crack closure in the fatigue crack propagation of a Cu-2wt.%Be alloy in dry air and ammoniacal solution

Abstract

Fatigue cracking was investigated by measuring the crack closure of unaged and peak-aged Cu-2wt.%Be alloy specimens in 0.05 M Cu2+ -containing 1 M ammoniacal solution using an unloading elastic compliance technique and by comparing the results with those obtained in dry air. The anodic behaviour of both kinds of specimen in the ammoniacal solution was also investigated by potentiodynamic polarization and potentiostatic current transient experiments. In dry air, a plateau in the fatigue crack propagation (FCP) rate vs. Delta K-eff plot was observed for both kinds of specimen at relatively high Delta K-eff values. This can be accounted for in terms of the retardation of FCP due to the accumulated strain released by the formation of a shear band at the crack tip. The intrinsic FCP rate of the unaged specimen in the ammoniacal solution exceeded that of the peak-aged specimen; however, the apparent value showed the opposite trend. The anodic dissolution of the unaged specimen in the ammoniacal solution was slightly larger than that of the peak-aged specimen. The unaged specimen showed a higher crack closure in the ammoniacal solution than the peak-aged specimen. The high crack closure of the unaged specimen in the ammoniacal solution is due to the relatively inhomogeneous deformation and severe corrosion attack compared with the peak-aged specimen.