Creep behaviour of a rapidly solidified Al-5Cr-2zr alloy between room temperature and 823 K

摘要

The flow behaviour of the rapidly solidified Al-5Cr-2Zr alloy investigated in this study is well described by the power law creep. Based on the stress sensitivity and the activation energy for creep encountered, three temperature ranges were defined: a low temperature range from 298 to 523 K with n > 20 and Qc = 77 kJ mol-1, an intermediate temperature range from 573 to 673 K with n close to 8 and Qc = 167 kJ mol-1, and a high temperature range from 723 to 823 K with n close to 8 and Qc = 273 kJ mol-1. In the low temperature range, creep rate is controlled by aluminium pipe diffusion. The high value of n > 20 could not be associated with any diffusion controlled dislocation creep mechanism. This behaviour can be rationalized using a substructure invariant model with a stress exponent of 10 and a threshold stress. In the intermediate temperature range, creep rate is controlled by aluminium lattice self-diffusion. The stress exponent and the activation energy obtained are consistent with the substructure invariant creep model. In the high temperature range, although the stress exponent suggests that creep may be explained by the substructure invariant model, the apparent activation energy is much higher than the activation energy for self-diffusion of pure aluminium, which may be attributed to the coarsening of dispersoids.