Effect of molybdenum content on phase transformations during continuous heating of metastable β Ti-Mo alloys

Abstract

Three metastable $β$ titanium alloys with different molybdenum contents, Ti-12Mo, Ti-15Mo and Ti-18Mo (wt.%), were investigated to determine the influence of $β$-phase stability on phase transformations during continuous heating. Electrical resistance measurement, dilatometry and differential scanning calorimetry were performed during linear heating at 5 °C/min up to 750 °C. The in-situ experiments were complemented by electron microscopy observations of specimens heated to selected temperatures and subsequently water-quenched. All alloys exhibited a sequence involving partial dissolution of athermal $ω$ phase, stabilization and growth of isothermal $ω$ phase, subsequent $ω$ dissolution and precipitation of $α$ phase. Increasing molybdenum content progressively suppressed $ω$ phase evolution and subsequent $α$ precipitation and narrowed the temperature interval associated with $ω$-related transformations. The excellent agreement between electrical resistance measurements, DSC, dilatometry and electron microscopy enabled a consistent description of phase evolution during heating and demonstrated the benefits of combining complementary experimental techniques for investigation of complex transformation pathways in metastable $β$ titanium alloys.