  The kinetics of primary alpha-Ti colony/Widmanstatten plate growth from the
beta are examined, comparing model to experiment. The plate growth velocity
depends sensitively both on the diffusivity D(T) of the rate-limiting species
and on the supersaturation around the growing plate. These result in a maxima
in growth velocity around 40 K below the transus, once sufficient
supersaturation is available to drive plate growth. In Ti-6246, the plate
growth velocity was found to be around 0.32 um min-1 at 850 oC, which was in
good agreement with the model prediction of 0.36 um min-1 . The solute field
around the growing plates, and the plate thickness, was found to be quite
variable, due to the intergrowth of plates and soft impingement. This solute
field was found to extend to up to 30 nm, and the interface concentration in
the beta was found to be around 6.4 at.% Mo. It was found that increasing O
content will have minimal effect on the plate lengths expected during
continuous cooling; in contrast, Mo approximately doubles the plate lengths
obtained for every 2 wt.% Mo reduction. Alloys using V as the beta stabiliser
instead of Mo are expected to have much faster plate growth kinetics at
nominally equivalent V contents. These findings will provide a useful tool for
the integrated design of alloys and process routes to achieve tailored
microstructures.
