Enhanced mechanical properties and structure stability induced by Si in Ti-8.5Al-1.5Mo alloys

The crystalline microstructures, mechanical properties and structural stability of Ti-8.5Al-1.5Mo-xSi (wt%, x=0%, 0.2%, 0.4%, and 0.6%) alloys were comprehensively investigated. It is shown that with the addition of certain amount of Si, Widmanstatten microstructure was refined and high density of dislocation lines was accumulated in β film and at the grain boundaries between α and β phase. The addition of 0.2% and 0.4% Si induced suppression of the transformations of α→α2, α2→α and α→β in heating process and slow-down of the coarsening tendency of Widmanstatten microstructure during the annealing process. It has been found that the addition of Si results in enhanced tensile mechanical properties and overcomes the strength-ductility trade-off, e. g. the fracture strength and elongation of the alloy with 0.2% Si were increased by 10.5% and 68.5%, respectively, as compared with those of Si free alloy. The strengthening and toughening mechanism are attributed to the solid solution strengthening of Si in α and β phase, the grain boundary and Cottrel atmosphere strengthening, and remaining β phase induced toughening.