Metastable Structures in a-b' 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 alpha-beta' (face centred cubic-B2 ordered) region of this binary system. Thermal treatments were also carried out to induce further changes and transformations to more stable states starting from the conditions attained with the mentioned non-equilibrium processes routes. In the rapidly solidified material, a body centred cubic structure was observed. At this stage the presence 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' mixture could be induced. A similar condition could also be achieved by grinding the starting melt-spun ribbons in a high energy ball-mill. The remarkable difference was that in this case the fee alpha -phase had a non-equilibrium composition, which is compatible with that of the parent beta'-phase. After heat treatment, the milled specimen has the same composition of the alpha -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 alpha-beta' mixture. Phase evolution and compositions were evaluated using X-ray diffraction analyses.