Designing shell-layer-core architecture in Ti-based composites to achieve enhanced strength and plasticity

Abstract

Developing novel high-strength titanium structural materials to achieve lightweight contributes to reducing CO2 emission. In by the multilayered structure of three-piece golf balls, we design a multimodal shell-layer-core microstructure in Ti68.8Nb13.6Co6Cu5.1Al6.5 composites and reveal the underlying mechanism of their microstructure evolution and mechanical properties. Herein, the multimodal shell-layer-core microstructure was attained via semi-solid sintering caused by the melting of CoTi2 phase with appropriate sintering process. Specifically, the ultrafine CoTi2 twins distributed along micron-sized β-Ti matrix form a shell structure around the β-Ti layer, while the nanostructured α' martensite is embedded and agglomerated in the center area of β-Ti matrix to construct a core region. Fundamentally, the unique structure stemmed from the appropriate sintering temperature, rapid cooling rate, and the suitable holding pressure during the sintering process. Such composites exhibited high compressive yield strength of 1614 MPa, ultimate strength of 3119 MPa with a large compressive strain of 38.6%, representing the highest values reported thus far in the literature. The high yield strength was attributed to the dislocation-blocking effect of CoTi2 twins and nanostructured α' martensite, while the improved ductility results from the micro-sized β-Ti matrix and the strain-hardening effect of α' martensite. This work provides fundamental insight into developing and fabricating strong-yet-ductile Ti-based composite materials for demanding structural applications.