Low cycle fatigue behaviour of a superplastic aluminium bronze

Abstract

Low cycle fatigue behaviour of a superplastic aluminium bronze (9.5 wt.-%Al and 4.0 wt.-%Fe) has been investigated over the temperature range from ambient to 1073 K. The results fit the Coffin-Manson law, δε_pN_f ^β = C, where ∆ε_p is the plastic strain range, N_f the number of cycles to failure, and β and C are constants. There were, however, certain deviations from the usual behaviour of non-superplastic metallic materials. These deviations may be summarized as: (1) an increase in fatigue life with increase in temperature above ∼773 K; (2) a decrease in the magnitude of the exponent β to values <0.5 with increase in temperature above ∼773 K; (3) a square-shaped mechanical hysteresis loop at 1073 K, the temperature of optimum superplastic deformation; and (4) specimen shape instability at 1073 K. These features have been explained in terms of the rapidly increasing sensitivity of the flow stress to strain rate and the rapidly decreasing flow stress as the temperature is raised.