Constructing a core-shell structure in Ti-based alloys with exceptional mechanical properties through semi-solid sintering

In this work, we developed a semi-solid sintering method for constructing a core-shell architecture in Ti68.8Nb13.6Co6.8Cr5.1Al6.5 alloy and revealed the underlying mechanism of microstructure evolution and deformation behavior. Fundamentally, the semi-solid state was achieved by sintering amorphous powders at temperatures between the melting point of the CoTi2 phase and the β-Ti matrix. During the process, the liquid CoTi2 phase was squeezed towards the β-Ti boundaries due to the sintering pressure and the growth of β-Ti grains. Subsequently, it transformed into a hard ultrafine CoTi2 phase distributed along the β-Ti boundaries, constructing a core-shell structure. The resulting core-shell structure exhibited a high compressive yield strength of 1560 MPa, an ultimate strength of 3006 MPa, and a remarkable compressive strain of 40.1%, surpassing typical Ti-based alloys under compressive loading. The high strength was attributed to dislocation-impeding effect of the CoTi2 phase, while the activation of multiple slip systems triggered by the CoTi2 shell contributed to plasticity. The results provide fundamental insights into the fabrication of Ti-based alloys with exceptional mechanical properties for structural materials applications.