Microstructural and Mechanical Property Development in Metastable Beta Titanium Alloys

The increased usage of titanium in aerostructural applications in recent years has necessitated a deeper understanding of microstructural-property relationships, along with the process dependence of these microstructures. Of particular interest are metastable beta titanium alloys, which have been the focus of this study. These alloys are destined for structural applications in civil and military aircraft owing to their relatively high strength and low density, coupled with good corrosion resistance (at low temperatures). The microstructural effects on key mechanical properties have been investigated, and the influence of thermomechanical processing on microstructure has been simulated.

This paper will present the morphological and volume fraction changes in both the primary and secondary alpha, together with the beta substructure evolution, providing insight into the observed variation in mechanical properties. In order to assess the effect of thermomechanical variables (strain, strain rate, strain path and temperature), hot torsion tests were carried out using an in-house ‘Arbitrary Strain Path’ test rig. Using this, the onset of various microstructural phenomena were observed, including the breakup of alpha ‘nodules’ and misorientation of beta subgrains. This microstructural evolution has been correlated with changes in mechanical properties. Ultimately, an appreciation of this behaviour should facilitate the manipulation of processing in order to yield superior performance and greater production efficiency.