Hierarchical structured Zn-Cu-Li alloy with high strength and ductility and its deformation mechanisms

Abstract

Although Zn-based alloys exhibit great potential as biodegradable implants due to their moderate degradation rate and acceptable biocompatibility, the mechanical property is insufficient to meet medical applications. In this study, a Zn-2Cu-0.8Li (wt%) alloy with both high strength and high ductility is developed via a unique hierarchical structure. The alloy is composed of a hard micron-sized β-LiZn4 matrix, a soft submicron η-Zn phase and dispersive ε-CuZn4 nanoprecipitates. The ε-CuZn4 nanoprecipitates grow along the specific direction and exhibit a coherent interface with the matrix. During the room-temperature tensile deformation, continuous dynamic recrystallization (CDRX) related to dislocation absorption and preferential misorientation increase near grain boundaries, as well as 〈c + a〉 dislocations, are observed. The excellent strength of the alloy is mainly attributed to the hard β-LiZn4 matrix with fine grains and the dispersive ε-CuZn4 coherent nanoprecipitates. Simultaneously, favorable ductility is ensured by the deformable matrix with fine grains, and further improved by the activated CDRX, 〈c + a〉 slip and soft submicron η-Zn phase. Owing to the unique hierarchical microstructure, Zn-2Cu-0.8Li alloy exhibits a yield strength of 426.2 MPa, ultimate tensile strength of 472.2 MPa, uniform elongation of 43.7% and fracture elongation of 63.7%, showing great prospects for broader biomedical applications. This research proposes a significant strategy for the design of Zn alloys with excellent combination of high strength and ductility.