Alpha phase precipitation in Ti-30Nb-1Fe alloys - phase transformations in continuous heating and aging heat treatments

Microstructure and mechanical properties of β metastable Ti-30Nb and Ti-30Nb-1Fe alloys subjected to different aging heat treatments were investigated. Various temperatures and heating rates were employed in order to determine their influence on α phase precipitation. The alloys were characterized by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning and transmission electron microscopy. Several mechanical properties were evaluated, such as Vickers hardness and elastic modulus, and tensile tests were also performed. The results indicate that the addition of Fe reduces the α phase precipitation and ω dissolution temperatures, although ω phase was still detected in Ti-30Nb-1Fe aged at 400 °C. The addition of Fe caused refinement of α phase precipitates, probably due to the higher diffusion coefficient of Fe. As for the influence of the heating rate, 2 and 30 °C/min did not cause significant microstructural changes. Finally, α phase refinement in Ti-30Nb alloy was favored by aging at 550 °C, at a heating rate of 600 °C/min.