Chapter 75 Dislocations and Twinning in Face Centred Cubic Crystals

Publisher This chapter describes the dislocation substructure in highly strained copper and copper alloy crystals initially oriented for single glide and have analyzed the consequences of passage through this complex structure of a twinning front. The relation among various types of dislocations in the parent and the twinned crystals and the nature of new lattice defects resulting from twinning is analyzed. Dislocation transformations can be classified into five groups, depending upon the character of the parent defect and its transformation product. The first group includes transformation of dislocations which are glissile in the matrix but sessile in the twin. The second group includes those dislocations, which are sessile in the matrix but become glissile in the twin. The next group, glissile to glissile transformations, includes all secondary dislocations having Burgers vectors in planes K1 and K2, which are undistorted by passage of the twinning front. These dislocations are important in the development of the three-dimensional dislocation substructure in the twin lattice. Next are the sessile to sessile transformations represented by faulted dipoles and their products. These defects have Burgers vectors normal to the K1 and K2 planes; they may or may not inherit similar structures in the twin lattice.