Immiscible nanostructured copper-aluminum-niobium alloy with excellent precipitation strengthening upon friction stir processing and aging

A ternary immiscible nanostructured Cu-Al-Nb alloy was fabricated by friction stir processing of mechanically compacted pellets. Subsequently, aging was carried out at 563 K for various times. The material exhibited hardness of similar to 43 +/- 0.1 GPa in the peak-aged condition (aging for 6 h), which is remarkable among Cu-based ternary immiscible alloys. The excellent strength of the material is attributed to Hall-Petch strengthening due to the extremely refined nanocrystalline structure, coupled with precipitation strengthening due to a uniform distribution of nano-scale Al- and Nb-rich precipitates or clusters, as confirmed by X-ray diffraction and microstructural characterization. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.