Study of microstructure and mechanical properties of oriented single colony crystals of a near-alpha titanium alloy at room temperature

Two phase alpha/beta titanium alloys have been widely reported to deform by primary creep at low homologous temperatures (T/Tm < 0.2) and at fractions (as low as 0.6) of the 0.2% yield strength. There exists little understanding of the mechanisms of creep deformation in these alloys. The mechanism of slip transmission across the alpha/beta interfaces is also not well understood.;Three distinct interfaces are commonly observed in these alloys---the prior beta grain boundary, the colony boundary and the alpha/beta interface. Interfacial sliding along the three boundaries has been reported in the literature under both constant strain rate deformation and also during primary creep deformation. The mechanism of interface sliding in these alloys is also not well understood.;Single colony crystals containing a single variant of alpha in a prior single crystal of beta were grown using a float zone technique. The single colony crystals were then oriented so that one particular slip system in the alpha phase has the highest resolved shear stress. Four different colony orientations have been tested in this study. Two colony crystals have the highest resolved shear stress on a <a> - prismatic slip plane, while the other colony orientations had the highest resolved shear stress on a <a> - basal slip plane. The two colonies oriented for <a> prismatic slip show an anisotropy in their deformation behavior under both constant strain rate and creep conditions. The two colonies oriented for <a> basal slip show a smaller anisotropy under constant strain rate testing. These colonies are more anisotropic in their creep behavior. The alpha/beta interfaces play a significant role in understanding the anisotropy in the mechanical deformation. The relative misalignment of the slip systems in the alpha and the beta phases and the differences in the lengths of the Burgers vector in the two phases has been used to explain the anisotropy in the deformation behavior. A possible explanation for the observed alpha/beta interface sliding has also been presented in this work.