Effect of Nb and Ta Addition on Deformation Mechanism and Tensile Properties of TiMoZr Alloys

Ti-8Mo-2Zr, Ti-8Mo-4Nb-2Zr and Ti-8Mo-4Nb-2Zr-2Ta (atom fraction/%) alloys were prepared by cold crucible induction levitation melting, rolling and solution treatment. The effects of Nb and Ta additions on the microstructure, tensile properties and deformation mechanism of the alloys were investigated. The results show that only one single β phase existed in all the three alloys. The β phase grain size decreased in turn with addition of Nb and Nb+Ta. Ti-8Mo-2Zr alloy deformed mainly by stress-induced α″ martensitic transformation and 332 twinning, while only dislocation slip appeared in the Ti-8Mo-4Nb-2Zr and Ti-8Mo-4Nb-2Zr-2Ta alloys. The change of deformation mechanisms led to the increase in alloy strength and decrease in ductility. The grain refinement strengthening effect and the solution strengthening effect produced by additions of Nb and Ta further improved the strength of the alloy; the tensile strength of the Ti-8Mo-4Nb-2Zr-2Ta alloy was as high as 970 MPa.