6 research outputs found
Interface characteristics in an {\alpha}+{\beta} titanium alloy
The alpha/beta interface in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) is investigated via
centre of symmetry analysis, both as-grown and after 10% cold work.
Semi-coherent interface steps are observed at a spacing of 4.5 +/-1.13 atoms in
the as-grown condition, in good agreement with theory prediction (4.37 atoms).
Lattice accommodation is observed, with elongation along [-1 2 -1 0]alpha and
contraction along [1 0 -1 0]alpha . Deformed alpha exhibited larger, less
coherent steps with slip bands lying in {110}beta. This indicates dislocation
pile-up at the grain boundary, a precursor to globularisation, offering insight
into the effect of deformation processing on the interface, which is important
for titanium alloy processing route design.Comment: Revised after revie
Interface characteristics in an α+β titanium alloy
The α/β interface in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) was investigated via center of symmetry analysis, both as-grown and after 10% cold work. Semicoherent interface steps are observed at a spacing of 4.5±1.13 atoms in the as-grown condition, in good agreement with theory. Lattice accommodation is observed, with elongation along [1210]α and contraction along [1010]α. Deformed α exhibited larger, less coherent steps with slip bands lying in {110}β. This indicates dislocation pile-up at the grain boundary, a precursor to globularization during heat treatment. Atom probe tomography measurements of secondary α plates in the fully heat-treated condition showed a Zr excess at the interface, which was localized into regular structures indicative of Zr association with interface defects, such as dislocations. Such chemo-mechanical stabilization of the interface defects would both inhibit plate growth during elevated temperature service and the interaction of interface defects with gliding dislocations during deformation
The Kinetics of Primary Alpha Plate Growth in Titanium Alloys
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.Comment: Revised version resubmitted to journa