(a, b) Schematic of the processing route to bioinspired, multiscale HFL microstructure alloy. Insets I and III show continuous extrusion and rotary swaging, respectively; inset II illustrates the design philosophy of dendritic hierarchies. (c) Typical optical microscopy (OM) image revealing the as-cast bar sample with a highly-developed dendrite structure from millimeter to micron scales. (d) Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) images revealing multiscale HFL structure. (e) Yield strength and uniform elongation versus conductivity compared with previously reported CuCrZr materials. (f) Multifunctional radar map of diverse property values or trends of both UFG and HFL samples. The wear resistance is expressed by the reciprocal of the wear weight loss. Thermostability refers to the ratio of the hardness after annealing at 550 ? for 3 h to that before annealing. (g) Potential applications of HFL-reinforced CuCrZr alloys include high-speed railway contact wires.
(a, b) Schematic of the processing route to bioinspired, multiscale HFL microstructure alloy. Insets I and III show continuous extrusion and rotary swaging, respectively; inset II illustrates the design philosophy of dendritic hierarchies. (c) Typical optical microscopy (OM) image revealing the as-cast bar sample with a highly-developed dendrite structure from millimeter to micron scales. (d) Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) images revealing multiscale HFL structure. (e) Yield strength and uniform elongation versus conductivity compared with previously reported CuCrZr materials. (f) Multifunctional radar map of diverse property values or trends of both UFG and HFL samples. The wear resistance is expressed by the reciprocal of the wear weight loss. Thermostability refers to the ratio of the hardness after annealing at 550 ? for 3 h to that before annealing. (g) Potential applications of HFL-reinforced CuCrZr alloys include high-speed railway contact wires.

High-performance, engineering applications demand a combination of critical properties in materials that can be mutually exclusive such as high strength and toughness. Natural materials, however, pull off this feat using self-assembled, hierarchical architectures. However, it remains challenging to tailor bioinspired structural hierarchies in bulk engineering materials.

Now researchers report that dendrites in metal alloys, which are usually regarded as undesirable, can be exploited to create bioinspired hierarchical structures that allow different reinforcement mechanisms to interact, boosting performance, particularly the combination of strength, ductility, and conductivity [Shi et al. Materials Today (2023), https://doi.org/10.1016/j.mattod.2023.11.003].

“We report a counterintuitive strategy exploring… highly-developed dendritic hierarchies in as-cast bulk alloys,” says first author of the study, Peijian Shi.

Dendrites in as-cast bulk alloys are usually eliminated in a sequence of costly and lengthy high-temperature annealing treatments. Instead, the researchers at Shanghai University, City University of Hong Kong, Max Planck Institute for Solid State Research, ASTAR, Johns Hopkins University, Shenyang National Laboratory for Materials Science, Nanjing University of Science and Technology, and Nanyang Technological University used thermomechanical processing to tailor the deformation, elongation, alignment, and refinement of dendrites to create a hierarchical fibrous lamellar (HFL) structure over multiple length scales. The resulting Cu-1.0wt%Cr-0.1wt%Zr alloys demonstrate a simultaneous yield strength of 655 MPa and elongation of 6.8%, high impact toughness, high electrical conductivity, and thermal stability.

“The record-high combination of strength, ductility, and conductivity in our HFL-reinforced CuCrZr alloys is superior to other types of state-of-the-art bulk copper alloys,” points out Huajian Gao.

The researchers believe the shell- or bamboo-like HFL structure encourages the consecutive interaction of multiple reinforcement mechanisms, synergistically combining to avoid the various typical trade-offs between physical properties. The high proportion of low-angle grain boundaries, for example, leads to grain-boundary strengthening and an ultrahigh yield strength. Nanoprecipitates, meanwhile, interact with gliding dislocations during deformation, leading to entanglement and accumulation.

“A high level of dislocations and their efficient accumulation operating in our innovative HFL structure also contribute to exceptionally sustainable hetero-deformation-induced (HDI) strain hardening,” says Yuntian Zhu.

For bulk as-cast alloys, introducing HFL microstructure could reduce manufacturing costs without sacrificing properties. The novel multifunctional alloys could prove useful for railway contact wires and networks, electric vehicles, and heat exchangers in fusion reactors, suggest the researchers. The strategy could also be extendable to other alloy systems, potentially changing the concept of designing high-performance, next-generation structural and functional integrated bulk engineering materials.

“Our HFL materials [are] truly multifunctional, which is of great importance [for applications],” says C. T. Liu. “And apart from high figure-of-merit multifunctionality, a grander impact of our bioinspired, heredity-derived strategy is that many distinct, previously unattainable technological advantages become available,” adds Yunbo Zhong.