Metastable structures in alpha-beta ' brass

Rapid solidification and mechanical grinding were used to induce metastable structures in a Cu-Zn alloy with a composition falling in the two phase al pha-beta' (face centred cubic-B2 ordered) region of this binary system. The rmal treatments were also carried out to induce further changes and transfo rmations to more stable states starting from the conditions attained with t he mentioned non-equilibrium processes routes. In the rapidly solidified ma terial, a body centred cubic structure was observed. At this stage the pres ence of long-range order could be inferred. Nonetheless, upon heat treating the material at 500 degreesC for 15 min the formation of the alpha-beta' m ixture could be induced. A similar condition could also be achieved by grin ding the starting melt-spun ribbons in a high energy ball-mill. The remarka ble difference was that in this case the fee alpha -phase had a non-equilib rium composition, which is compatible with that of the parent beta'-phase. After heat treatment, the milled specimen has the same composition of the a lpha -phase as the one found in the melt-spun heat treated materials. These results indicate a diffusionless transformation was induced by the milling process into the as-spun material from the parent beta'-phase into the alp ha-beta' mixture. Phase evolution and compositions were evaluated using X-r ay diffraction analyses. (C) 2001 Elsevier Science B.V. All rights reserved .