Effect of compositional heterogeneity on the mechanical properties of a single-phase Cu-9Al alloy with different grain sizes

Recent investigations have indicated that compositional heterogeneity, which is compositional undulation of alloying elements in single-phase solid solutions, can enhance the strength without sacrificing ductility, similar to cluster strengthening, of single-crystal nano-pillars and bulk nanocrystalline metallic materials. However, the impact of compositional heterogeneity on the mechanical properties of coarse-grained metallic materials is not yet fully understood. In this study, we examine the influence of compositional heterogeneity on the tensile mechanical properties of a Cu-9Al (at.%) alloy with a coarse-grained structure fabricated using wire arc additive manufacturing and with an ultrafine-grained structure after further processing. Our results demonstrate that the effects of compositional heterogeneity depend significantly on the grain size. Specifically, in ultrafine-grained samples, there is a remarkable improvement in strength with only a slight reduction in ductility. However, as grain size increases, the strengthening effect of compositional heterogeneity diminishes, resulting in softening with a significant loss of ductility. These phenomena can be attributed to the behaviour of dislocations in the materials. Overall, this study highlights the importance of understanding the relationship between compositional heterogeneity, grain size, and mechanical properties in metallic materials, which can inform the design of new materials with improved strength and ductility.