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The influence of transformation temperature on microtexture development associated with a precipitation at b/b grain boundaries (GB) in the near-b Ti17 alloy was studied using electron backscatter diffraction and considering isothermal treatments. For the alloy studied and the temperature range considered, decreasing the transformation temperature decreased the local microtexture strength within each prior b grain because of a larger number of a WGB colonies (standing for a Widmanstätten GB) formed per b grain, each colony increasing by one the number of a orientations inside each prior b grain. This larger number of a WGB colonies was a consequence of faster formation along b/b GB of their precursors, the allotriomorphic a GB grains (standing for a-GB) at lower transformation temperatures, as evidenced by detailed examination of the first stages of a GB formation. a GB crystallographic orientations frequently followed a variant selection (VS) criterion based on the alignment of (0 1 1)b//(0 0 0 1)a GB //(0 1 1)b. From a statistically relevant number of observations, VS was found to be more frequent at a lower transformation duration and a lower temperature, but the effect was not significant enough to influence the final a microtexture, considered at the scale of one prior b grain. a GB grains that followed the VS criterion emitted two a WGB colonies on either side of the b/b GB more frequently than those with no particular orientation.

International audienceWe have investigated the microstructure evolutions in the Ti17 near Click to view the MathML source titanium alloy during heat treatments. The phase transformation has first been studied experimentally by combining X-ray diffraction analysis, electrical resistivity and microscopy observations. From a series of isothermal treatments, a IT diagram has been determined, which takes into account the different morphologies. Then, a Johnson–Mehl–Avrami–Kolmogorov (JMAK) model has been successfully used to describe the phase transformation kinetics during either isothermal or cooling treatments. Finally, the coupling of the JMAK model to the finite element software ZeBuLoN allowed us to investigate the evolution of the spatial distribution of the different morphologies during the cooling of an aircraft engine shaft disk after forging

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