Short range order in copper-aluminium alloys

Abstract

In a slowly cooled copper-aluminium alloy containing 15 at.% Al a marked surge of energy absorption occurs in the range of temperature 226-290°C on continuous heating at 2°C/min; beyond 290°C energy is absorbed at a constant rate. The magnitude of the initial surge, the range of temperature of the surge and the constant rate of absorption of energy vary with the aluminium content of the alloy. The absorption of energy is attributed to the destruction of short range order. The magnitude of the initial surge increases on annealing specimens at 155°C and this is attributed to an increase in the degree of short range order by the annealing treatment. Quenched specimens evolve energy in two stages (stage 1 occurs below 150°C and stage 2 above this temperature) and these stages are accompanied by decreases in electrical resistivity. The magnitude of the stages varies with the quenching temperature for a constant composition of the alloy and with composition for a constant quenching temperature. The evolutions of energy and the decreases in resistivity in both stages 1 and 2 are attributed to the return of short range order, this process being assisted by quenched-in vacancies in stage 1. As the quenching temperature increases considerable reordering occurs during cooling from the quenching temperature and the variation in annealing behaviour with quenching temperature and composition is interpreted in terms of the degree of disorder and the concentration of vacancies retained by quenching. © 1963.