Criteria for fast and selective α precipitation at β grain boundaries in Ti-alloys Consequence for in-service microstructures

The potential for β grain boundaries (GBs) to give rise to large Widmanstätten colonies was determined through the observation of a large amount of precipitates at β GBs in a β-metastable titanium alloy using electron backscatter imaging and diffraction. The most critical boundaries are those which transform early and where a type of Variant Selection (VS) called double Burgers VS occurs. This mechanisms take place at ‘special’ β boundaries misoriented so that an α precipitate can be related to both grains through the Burgers relation. It was shown that the most critical GBs have a disorientation at an angle of less than 10° from 49.5°/ or 60°/ . A simulation study allowed those boundaries to be quantifed in crystallographic textures typical of industrial products. Those texture have then been discussed as a function of their potential to form large Widmanstätten colonies.