Flow behaviour of Nickel Aluminium Bronze under hot deformation

Flow behaviour of a Nickel Aluminium Bronze (NAB) alloy under hot compressive deformation was investigated using a deformation dilatometer. Temperatures of 1023, 1073, 1123 and 1173 K and strain rates of 0.1, 1.0 and 10 s−1 were used as the forming parameters. The experimental results showed that true stress–strain curves of the alloy exhibited dynamic recovery and dynamic recrystallisation with single-peak stress. Dynamic recovery was dominant at higher temperature and lower strain rate. The peak stress increased as the strain rate and temperature increased. The peak strain also increased with increasing strain rate. However, it was independent of temperature. The flow curves can be represented by the hyperbolic-sine law Arrhenius equation with activation energy of 514.25 kJ/mol. Comparisons between predicted flow stresses and experimentally determined results showed that the developed constitutive models were sufficiently accurate to demonstrate flow behaviour at high temperatures of the NAB alloy. This was supported by a correlation coefficient R of 0.981 and an average relative error of 13.42% for the particular test conditions. Dynamic material modelling approach has been used to describe flow stability/instability. For the NAB alloy, the criterion of the strain rate sensitivity, the criterion with regard to the variation of strain rate sensitivity with log ε̇ and the criterion of the temperature sensitivity were always satisfied. The critical criterion is the rate of change of the temperature sensitivity with respect to log ε̇.