Thermomechanical Processing, Phase Transformations and Mechanical Properties of Ti-25Al-10Nb-3V-1Mo.

Increasing niobium content is known to increase strength, toughness and ductility of Ti{sub 3}Al-based alloys by stabilizing the orthorhombic phase (Ti{sub 2}AlNb), at the expense, however, of density. It will be shown, that the alloy Ti-25Al-1-Nb-3V-1Mo, having a relatively low content of {beta}-stabilizing elements, can be processed in a way to produce a high volume fraction of the orthorhombic phase with a fine microstructure. As a result, extremely high yield strength values close to 1,400 MPa at reasonable room temperature ductility of about 3% can be observed. To produce such microstructures, phase transformations needed to be known in Ti-25Al-10Nb-3V-1Mo and were investigated by TEM and XRD. A new TTT-diagram will be proposed and related to the observed microstructures and mechanical properties. Depending on the microstructure, an extreme variation of the tensile strength and deformation behavior can be obtained.