Thermal Stability of Athermal ω-Ti(Fe) Produced upon Quenching of β-Ti(Fe)

Abstract

This work shows the formation of the athermal ω phase in alloy Ti–4 wt% Fe. The alloy under study, heat treated at 800 °C for 100 h and subsequently water quenched, is investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The thermal stability of ω-Ti(Fe) is investigated by differential scanning calorimetry (DSC). The DSC measurements show a cascade of several thermic events between 160 and 450 °C, and one strong and sharp exothermic DSC peak at ∼480 °C. The phase transformations and other microstructural changes behind these events are explained by complementary use of XRD, electron backscatter diffraction (EBSD), and TEM analyses that are performed on samples heated stepwise in the DSC apparatus. These experiments indicate that the embryos of athermal ω-Ti(Fe) grow up to ∼400 °C and start to decompose into an α-Ti(Fe) + β assemblage already at 450 °C. At ∼480 °C, the decomposition of the athermal ω-Ti(Fe) phase is practically finished. Thermal stability of athermal ω-Ti(Fe) is compared with the thermal stability of ω-Ti(Fe) produced in a high-pressure torsion (HPT) process, indicating a higher thermal stability of ω-Ti(Fe) in the non-deformed alloys.