Overcoming silicon embrittlement in ultra-high-Si β-21S composites via solution treatment

For titanium matrix composites (TMCs), controlling the content of reinforcing phases is one of the key factors affecting mechanical properties. In this study, β-21S alloy (Ti-15Mo-2.7Nb-3Al-0.2Si) with excellent comprehensive properties was selected as the matrix. β-21S-based composites with different compositions were fabricated via hot pressing sintering by incorporating high contents of Si and a certain amount of TiB. Microstructural characterization and mechanical property evaluation of the as-sintered composites revealed that the volume fractions of precipitated α-phases and silicides increased with increasing Si content. Specifically, the TiB/β-21S-0.7Si composite exhibited a high strength of 1400 MPa, while its ductility was merely 2% due to the presence of continuous grain boundary silicides. Subsequent solution heat treatment at 1300 °C for 2 h was performed on the as-sintered composites. Results showed that complete dissolution of intragranular silicides and α-phases was achieved, and the number of thin shell-like S1-type silicides at grain boundaries was reduced with a discontinuous distribution. Notably, the ductility of the solution treated TiB/β-21S-0.7Si composite was dramatically improved from 2% to 24%. Fracture analysis confirmed distinct ductile fracture characteristics of the solution-treated composite. Thus, rational heat treatment processes can effectively optimize the properties of high-Si-content TiB/β-21S-xSi composites, providing a feasible strategy for the development of high-performance TMCs.