Crystallographic Features of Phase Transformations during the Continuous Cooling of a Ti6Al4V Alloy from the Single-Phase β-Region

Crystallographic relationships between alpha- and beta-phases resulting from phase transformations, which took place during the continuous water quenching (WQ), air cooling (AC) and furnace cooling (FC) of a Ti6Al4V plates solution treated at 1065 degrees C, were investigated by methods of electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). WQ, AC and FC resulted in typical martensite, basket-weave and parallel-plate Widmanstatten structures, respectively. The experimental distribution of alpha/beta-misorientations deviated from BOR at set discrete angles close to 22, 30, 35 and 43 degrees. The experimental spectra of angles were confirmed by theoretical calculations of the possible misorientations between the alpha and beta phases through the beta(o)->alpha ->beta(II) -transformation path based on Burgers orientation relationship (BOR). Joint analysis of the experimental data and theoretical calculations revealed that the secondary beta(II)-phase was precipitated according to the sequence beta(o)->alpha ->beta(II) during continuous cooling from the single-phase beta-region. Similar spectra for alpha/beta-phase misorientations for all investigated cooling rates acknowledged the similar transformation mechanisms and dominant shear component of the phase transformations.

Automated summary

The crystallographic relationship between alpha- and beta-phases resulting from phase transformations during different cooling methods of Ti6Al4V plates were investigated through experimental data and theoretical calculations. It was found that the secondary beta(II)-phase occurred in a specific sequence during continuous cooling, and the orientations differences between alpha- and beta-phases showed a certain distribution pattern at discrete angles.