Achieving high strength and toughness by engineering 3D artificial nacre-like structures inTi6Al4V-Ti metallic composite

Abstract

Bio-inspired mimicking natural structures generally duplicate the three dimensional “hard brick-and-soft mortar” structure that may overcome the intrinsic brittleness of the brick, resulting in an improved mechanical performance. Here for the first time, we proposed an anti-bioinspired strategy of designing metallic composite with soft bricks (pure Ti) confined by hard mortars (Ti6Al4V alloy). The three-dimensional minority of hard mortar (with a volume fraction of ∼14%) is fabricated by using selective laser melting (SLM), while the bricks are introduced by filling the pure titanium powders followed by the hot isostatic pressing. The resulting nacre-like structured composite reveals a distinct periodic distribution of “soft-brick” and “hard-mortar” domains by a well-bonded interface with a well-bonded interface between them. This unique composite structure exhibits a combination of high strength and high fracture toughness that both exceed the respective value calculated using the rule of mixtures (ROM). Three dimensional heterogenous plastic deformations between the two domains induce the mechanical incompatibility, which has been confirmed by the presence of higher density of geometrically necessary dislocations (GNDs) in front of the interface. The large amount of GNDs was believed primarily responsible for the extraordinary strengthening and toughening beyond the ROM. This novel strategy of designing artificial three dimensional “soft brick-and-hard mortar” structure could be further applied to other metals and alloys, shedding lights on the development of innovative heterogeneous materials relevant to industry.