Effect of Ordering on Monovacancy and Divacancy Formation inβ-Brass Observed by Positron Annihilation

Measurements of the trapping of positrons in $\beta$-brass have shown that the vacancy formation energy dramatically increases with the ordering of the alloy below the order-disorder transition temperature. Based on predictions from our trapping-model analysis of the monovacancy behavior, we have searched for, and found above 430°C, direct evidence for the cusp-shaped rise in the trapping of positrons by divacancies that is characteristic of the rapid growth in the thermal divacancy population as the order parameter goes to zero.