Origin of dislocations within tensile and compressive twins in pure textured Zr

Dislocations and twins play an important role in the plastic deformation and hardening response of Zr. At 77 K, rolled Zr deforms by {1 1 over(2, ̄) 2} 〈 1 1 over(2, ̄) over(3, ̄) 〉 compressive twins and {1 0 over(1, ̄) 2} 〈 1 0 over(1, ̄) over(1, ̄) 〉 tensile twins, depending upon the orientation of the compressive axis with respect to the basal pole texture of the specimen. Here, for the first time, detailed transmission electron microscopy characterization of dislocations within the twins themselves - with an emphasis on the question of their origin - has been performed for pure Zr samples compressed to ∼4% at 77 K. The possible transformation of matrix dislocations by twin-associated reorientation was considered and tested using dislocation transformation matrices. This analysis shows that, while the above-mentioned mechanism generates sessile c- and a-type dislocations inside twins, a large number of dislocations inside the twins are glissile a-type and are generated after the twin has formed. The type and proportion of these dislocations vary, depending on the type of twin.