Interaction Mechanism Between Dislocation/Deformation Twinning And Interface In Titanium Alloys

{332}<113>twins and dislocation slips are very popular in deformed metastable βtitanium alloys and grain boundaries act as strong barrier to them in titanium polycrystals.Experimental results indicate that the misorientation angle on both sides of grain boundaries play an important role in the interaction between dislocations,twins and grain boundaries.Dislocations and twins can transfer at low angle grain boundaries while are mostly blocked by grain boundaries with high misorientation angle.However,slip or twin transmission at high angle grain boundaries can also be observed in deformed titanium alloys but there is still a lack of systematic research on this phenomenon.Besides,cross twins are very popular in slightly deformed Ti-15Mo alloys,which is much different from hcp metals,but the theoretical explanation for this phenomenon is still insufficient.Research on these interface coordinate issues is extremely important for understanding plastic deformation mechanism of titanium polycrystals.In this paper,the interaction between dislocations and {332}<113>twins and grain boundaries with different misorientation angle in Ti-5553 and Ti-15Mo are studied by scanning electron microscope and electron backscatter diffraction.The phenomenon of twin and slip transmission as well as twin and slip blocked were analyzed by combining residual Burgers vector,geometric compatibility factor and Schmid factor.The research results about the interaction between dislocations and grain boundaries in Ti-5553 indicate that dislocation slip can not only pass through low angle grain boundaries but also the high angle grain boundaries.However,geometric compatibility factor will decrease while residual Burgers vector magnitude increase,which indicates that slip transmission at high angle grain boundaries may cause strain concentration on one side of the grain boundary.The geometric compatibility factor can be used to induce the orientation of adjacent grains that is most conducive to slip transfer.The research results about the interaction between {332}<113>twins and grain boundaries in Ti-15Mo indicate that twins that transferred at grain boundaries have a good geometric alignment relationship,twins blocked by grain boundaries mostly due to the absence of potential twin variants that align well with twins in neighboring grains.Even if there are potential twinning variants in some neighboring grains,the Schmid factor of these variants are usually very small and the nucleation of twins in neighboring grains is very difficult.Finally,it is difficult for twins to pass through grain boundaries and this condition mostly appear at high angle grain boundaries.The statistical results show that the difference between twin transmission and twin blocked at large angle grain boundaries is largely caused by the difference in Schmid factors of twinning in neighboring grains.Except for grain boundaries,twin boundaries are also observed inside almost every grain.The formation of {332}<113>cross twins in Ti-15Mo alloys are a little different from which in HCP metals and no secondary twins were observed at the intersection of {332}<113>twins.Besides,the orientation of the intersection is close to one of the cross twins.The formation mechanism was found after observing cross twins after biaxial deformation.After that,the mechanical properties of Ti-15Mo after unidirectional and bidirectional predeformation were tested and the discrepancy in three directions were analyzed from the viewpoint of detwinning,twin-twin interaction,dislocation-twin interaction,stress-induced martensitic transformation and so on.