Heterogeneous distribution of isothermal ω precipitates prevents brittle fracture in aged β-Ti alloys

Isothermal omega (omega(iso)) precipitates in beta Ti-alloys can increase the yield strength of the material, but unfortunately at a dramatic cost of the ductility. The embrittlement is mainly attributed to the suppression of twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects, as well as the formation of dislocation channels associated with localized deformation. To address this issue, we propose a heterogenous microstructure in Ti-15Mo-3Al alloy using conventional rolling method, in which the heterogeneous distributions of both Mo element and omega(iso)precipitates are realized after aging. Both the nano-hardness and elastic modulus of omega(iso)rich (Molean) regions are larger than that of omega(iso)depleted (Mo-rich) regions. A four-time increase in tensile ductility is achieved in the heterogeneous microstructure without a loss of tensile strength, compared with the homogeneous counterpart. The ductility improvement can be ascribed to the blocking effect of omega(iso)depleted regions against the propagation of dislocation channels which later evolve into micro-cracks.

Automated summary

A heterogeneous microstructure in Ti-15Mo-3Al alloy with heterogeneous distributions of Mo element and omega(iso) precipitates has achieved a four-fold increase in tensile ductility without a loss of tensile strength, by blocking the propagation of dislocation channels and preventing the formation of micro-cracks.