On the formation of vacancy clusters in aluminium

Abstract

The formation of vacancy clusters in a single crystal of zone-refined aluminium with a dislocation density 500 to 1000 lines per cm², was studied during furnace heating and cooling between 218°C and 374°C by x-ray diffraction topography. The heating and cooling rate was approximately ½°C per sec. Black dots on the topographs, interpreted as dislocation loops in the crystal, were formed subsequent to both down-quenching and up-quenching when the vacancy supersaturation or inverse sub-saturation was sufficiently high. The critical supersaturation was 2·5±10% within the experimental uncertainty, and the critical inverse sub-saturation was somewhat higher. The clusters developed during growth into a dislocation network. When clusters were not formed, dislocation loops in rows were formed.