Generation of aligned precipitates in Cu-Zn-Al single crystals

Abstract
Several thermal treatments are known from literature to generate different distributions of y phase precipitates in Cu-Zn-Al alloys with martensitic transformation temperatures below room temperature. Some of these treatments are composed of a first quench followed by a flash heating to 670K for different times up to hundreds of seconds. The same type of treatments have been used in a Cu - 12.7Zn - 17.7Al ailoy (% at, e/a = 1.48) with a nominal Ms of 320 K, in order to study the influence of the precipitates on the martensite stabilization. In step-quenched specimens, the martensite stabilization by quenching was small and the precipitates obtained after the flash heating were homogeneously distributed, like in the alloys with low transformation temperatures. However, the specimens directly quenched to martensite exhibited a strong stabilization degree. After the subsequent flash heating, the distributions of precipitates clearly showed particular alignments along the boundaries of the martensite plates existing before the flash heating, as well as along the basal plane of certain martensite plates. In the present work the characteristics and mechanisms of formation of these particular distributions of precipitates will be discussed.