Rapid solidification and mechanical grinding of Cu-Zn alloys

Rapid solidification was used to prepare metastable Cu-Zn alloys having a composition close to the β-brass interval. In the as-spun condition ribbons had a body centred cubic (bcc) crystal structure, typical of β-brass. After isothermal heat treatments at 400°C such a structure was turned into a mixture of the initial bcc one plus the α phase of brass, having a face centred cubic (fcc) structure. A similar transformation could be also induced by ball-milling. Indeed the mentioned mixture was evolved from the same initial cubic phase by milling the as-spun ribbons in a high energy planetary mill From x-ray diffraction data it was not only possible to follow the phase evolution, but also to evaluate the composition of the two Cu-Zn phases from lattice parameters data. The α phase obtained by ball-milling was estimated to have off equilibrium compositions. Equilibrium conditions were established by heat treating the milled powders at selected temperatures. The stability of the different structures obtained in the course of the present investigation was checked using Differential Scanning Calorimetry (DSC) measurements. In the milled samples, when heated up in the calorimeter, it was noticed the occurrence of exothermic irreversible transformations, to be ascribed to recrystallisation and recovery.