Effect of prior α2 phase on precipitation kinetics of O-phase in advanced Ti2AlNb alloy

To study the influence of prior a2 phase on O-phase formation kinetics in /3 matrix, different isothermal heat treatments were performed at 876 and 780 degrees C using an advanced Ti2AlNb alloy with varying fraction of a2 phase. The kinetics of phase transformations was followed by electric resistivity measurements coupled to multi-scale microstructure characterization using scanning and transmission electron microscopy, energy dispersive X-ray spectrometry (EDS) and quantitative X-ray diffraction. It is revealed that the effect of a2 phase on the formation of O-phase depends on transformation temperature: while at 876 degrees C prior a2 precipitates lead to significantly slower formation of O-phase, as compared to a2 free alloy, the kinetics of O-phase formation is faster at 780 degrees C in the presence of a2 phase. Using EDS data as well as accurate measurements of lattice parameter of /3 phase, the diffusion character of O-phase formation in /3 matrix with and without prior a2 is shown for 876 degrees C while at 780 degrees C the diffusionless character of the O-phase formation is revealed for the beginning of the transformation followed by the partitioning of the alloying elements for prolonged treatment durations.

Automated summary

Isothermal heat treatments at 876 and 780 degrees C were performed on a Ti2AlNb alloy with varying fraction of a2 phase to study the influence of prior a2 phase on O-phase formation kinetics in /3 matrix. The kinetics of phase transformations were investigated using electric resistivity measurements, scanning and transmission electron microscopy, energy dispersive X-ray spectrometry, and quantitative X-ray diffraction. The results showed that the effect of a2 phase on O-phase formation depends on the transformation temperature. At 876 degrees C, prior a2 precipitates led to slower O-phase formation compared to the a2 free alloy, while at 780 degrees C, the presence of a2 phase accelerated the kinetics of O-phase formation. Diffusion and diffusionless character of O-phase formation in /3 matrix with and without prior a2 were observed at 876 and 780 degrees C, respectively.