Effect of dislocation substructure on the primary creep behavior of alpha titanium at elevated temperature
Constant stress creep tests were performed in vacuo on alpha titanium in various thermomechanical treatments.
At 500°C and 527°C annealed alpha titanium exhibits an anomalous creep arrest in the initial portion of the creep curve. After this creep arrest the creep curves swept up to a true steady state creep rate. This anomalous behavior is attributed to dynamic strain aging. The effect vanishes due to interstitial solute depletion as the interstitials are swept from the lattice by moving dislocations.
The prestrained and recovered samples tested at 60006 did not show a creep arrest. This is attributed to even distribution of interstitials on the recovered dislocation substructure making dynamic strain aging less effective. Additionally, transmission electron microscopy indicates that the tilt boundaries of the recovery structure can break down during the initial portion of the creep curve releasing mobile dislocations.
In steady state all conditions tested developed a dislocation subgrain substructure. The tendency for dislocation subboundaries to inhabit specific planes is not as marked as it is in the recovered structure.