Zhang Jie-Wen, Beyerlein Irene J, Han Wei-Zhong
Center for Advancing Materials Performance from the Nanoscale, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
Mechanical Engineering Department, Materials Department, University of California, Santa Barbara, California 93106-5070, USA.
Phys Rev Lett. 2019 Jun 28;122(25):255501. doi: 10.1103/PhysRevLett.122.255501.
Nanolayered, bimetallic composites are receiving increased attention due to an exceptional combination of strength and thermal stability not possible from their coarse-layered counterparts or constituents alone. Yet, due to their 2D planar, unidirectional arrangement, they are highly anisotropic, which results in limited strain hardening and ductility. Therefore, like many high-performance, ultrastrong materials of our time, they succumb to the usual strength-ductility trade-offs. Here we present the formation of a novel hierarchical microstructure, comprised of crystals consisting of 3D nanolayered α/β-Zr networks. By direct comparison with coarse-layered material of the same chemistry, we show that the unusual hierarchical 3D structure gives rise to high strain hardening, high strength, and high ductility. Using TEM analysis and hysteresis testing, we discovered that the 3D randomly oriented biphase boundaries result in progressively dispersive rather than localized slip with increasing strain. Dislocation activity in the α-Zr lamellae transitions from single slip to multislip and eventually to multimodal slip as strain increases. The diffusive slip-promoting properties of 3D layered networks can potentially invoke simultaneous high strength, strain hardening, and ductility, and reveal a new target in the microstructural design of high performance structural materials.
