Order-disorder phenomena in α -brass II. Influence of quenching

The transformation from disorder to partial order which occurs during slow cooling α-brass (part I) may be suppressed by quenching. The return of order in specimens water-quenched from 300 and 600 °C on heating from room temperature to 300 °C has been studied by differential calorimetry and by measurements of electrical resistivity, density, lattice parameter and hardness. The results indicate that specimens quenched from 600 °C reorder rapidly below 160 °C to a higher degree of order than that in slowly cooled specimens. For specimens quenched from 300 °C the initial degree of disorder is greater and reordering slower, the state characteristic of slowly cooled specimens being reached only at 245 °C. The activation energies for reordering are 1⋅2 and 1⋅7 eV for specimens quenched from 600 and 300 °C, respectively. The different behaviour after quenching from 600 °C is attributed to a higher concentration of quenched-in vacancies. Neither set of specimens exhibits appreciable co-operative disordering. However, in specimens quenched from 600 °C, reordered by heating to 160 °C and then quenched, further ordering followed by equivalent disordering takes place on reheating to 170 °C. This process is probably vacancy assisted. The excess vacancies appear to anneal out between 160 and 245 °C, but any accompanying changes in properties are masked by order-disorder phenomena. No changes in hardness are found to accompany reordering in quenched specimens.