Structural characterization of the {11■2} twin boundary and the corresponding stress accommodation mechanisms in pure titanium

Bingqiang Wei，Song Ni，Yong Liu，Min Song

State Key Laboratory of Powder Metallurgy, Central South University

摘 要：{11-22} compression twin plays an important role in accommodating deformation along the c axis of HCP metals.However,the studies on the interface structure of {11-22} twin boundary（TB）,especially the twin tip,and the corresponding local stress release mechanism are still limited.This work studied the interface characters of {11-2 2} TB of a deformed pure titanium by transmission electron microscope.The {11-2 2} TB presented serrated character,consisting of coherent twin boundary（CTB） and（0002）_T//（11-2-2）_M or（11-2-2）_T//（0002）_M steps,and the twin tip was fully composed of the basal-pyramidal（BPy）and pyramidal-basal（PyB） steps.The twin tip presents asymmetric morphology and the step height at the twin tip is much larger than that away from the twin tip.Two types of local stress accommodation mechanisms were observed:zonal dislocation emission and hexagonal close packed structure to facecentered cubic structure transformation.The zonal dislocation was produced by the dissociation of the1/3 <11-2-3><c+a> dislocation that was nucleated at the twin tip and the phase transformation was introduced by emission of Shockley partial dislocations from the {11-22} twin boundary.

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