Bio-Mimic Ti-Ta Composite with Hierarchical 'Brick-and-Mortar' Microstructure

Abstract

Nature materials, such as bones and nacre, achieve excellent balance of toughness and strength via a hierarchical "brick-and-mortar" microstructure, which is an attractive model for engineering materials design. Here, we produced nacre-like Ti-Ta metallic composites via a powder metallurgy process, during which milled powders were sintered by spark plasma sintering, followed by hot rolling and then annealing. The structure consists of soft Ta-enriched regions and hard Ti-enriched regions in a hierarchical and laminated fashion. The microstructural heterogeneity spans several scales due to the diffusion between Ti and Ta. This yields a novel metal-metal composite with a balanced combination of strength and ductility (1226 MPa ultimate tensile strength and 20.8% elongation), outperforming most of conventional Ti based alloys and composites. Via complementary in situ synchrotron X-ray diffraction and electron microscopies, it is found out that multiple micromechanisms are active, including nano-particle and dislocation localized strengthening as well as a "phase transformation induced plasticity. The manufacturing route developed here is versatile, capable of making high performance bio-mimic metallic composites.