Antiphase boundary energies and the transition from shearing to looping in alloys strengthened by ordered precipitates

The critical particle diameter for the transition from shearing to looping, <d>_max, during deformation of alloys strengthened by strong ordered coherent precipitates is related to the antiphase boundary (APB) energy on the {111} planes of the precipitate phase. Theoretical analysis of this process predicts average APB energies of 0.112± 0.030 and 0.161 ±0.024 Jm^-2 for the δ' (Al₃Li) and γ' (Ni₃Al) phases respectively. The value for the δ' phase is about 25% lower than those determined by nearly all other methods, while that for the γ' phase is about 15% higher. The present method of analysis is more reliable than that of a recent theory proposed by Glazer and Morris. However, because <d>_max cannot be measured with the same degree of precision as other quantities, it is argued that more accurate APB energies can be extracted from the analysis of other data on precipitation hardening of alloys containing ordered coherent precipitates.