Strengthening of cast Ti-25Nb-3Mo-3Zr-2Sn alloy through precipitation of α in two discrete crystallographic orientations

A detailed study of the microstructural development during aging of a Ti-25Nb-3Mo-3Zr-2Sn alloy is presented. Transmission electron microscopy observations show the as-cast microstructure is comprised of large beta grains containing fine coherent omega precipitates. Fine scale a laths form in two different crystallographic orientations throughout the beta matrix when the alloy is aged directly from the as-cast condition. The alpha laths typically have habit planes close to {1 1 1}(beta) or {2 3 3}(beta). Aging at 450 degrees C doubles the yield strength as compared to that in the as-cast condition. We suggest that the differently orientated alpha laths may contribute to this significant increase in the strength of the alloy. Martensitic alpha '' phase, with its habit plane close to {4 3 3}(beta), was observed in the as-cast microstructure subsequent to deformation. (C) 2010 Elsevier B.V. All rights reserved.