Local Atomic Arrangements and Anomalous Behavior in αCu–Al Alloys

Abstract

The anomalous specific heat of quenched alpha Cu–Al alloys with 15.5 at% Al has been investigated together with anomalies in electrical resistivity and micro Vickers hardness. The former anomalies take place in three stages; namely, the first two (stages I and II) are a heat evolution occurring below and above 150°C, and the other (stage III) is an absorption in the temperature range between 240 and 300°C. An attempt is made to elucidate the origins of the experimental results, which are interpreted as follows:(1) The anomaly in stage I is due to the formation of short range order in the process of disappearance of quenched-in vacancies and to the aggregation of solute atoms to defects.(2) The anomaly in stage II is due to the further development of short range order associated with the dispersion of solute atoms which have been trapped to defects in stage I, in addition to the ordering by migration of vacancies towards a thermal equilibrium state.(3) The anomaly in stage III is due to the destruction of short range order, which has been formed in the process of quenching as well as in stages I and II.