Diffraction contrast images of interphase boundaries in cobalt

Abstract

The boundaries between HCP and FCC phases in cobalt are generally expected to be of the type {111}FCC ‖ {001}HCP. Observations carried out by the authors indicate that the contrast exhibited by this type of boundary is very similar to the contrast exhibited by twin boundaries, as discussed by Sheinin and Corbett. These authors showed that images of twin boundaries consist of two intersecting sets of fringes with the possibility that one set is suppressed under certain diffraction conditions. The purpose of the work presented in this paper is to investigate the contrast exhibited by boundaries between the same two phases but which lie in a different habit plane.Experimental observations were carried out on boundaries in wedge crystals of cobalt, as shown schematically in Fig.1. The orientations of the crystals on either side of the boundary were obtained from selected area diffraction. For the bright and dark field images in Figs. 3a and 4a the orientations were found to be (12 )FCC on the left of the boundary and (100)HCP on the right. The boundary was found to be of the {111}FCC ‖ {312}HCP type. In the diffraction pattern obtained from the region containing the boundary shown in Fig. 2, the reflections (111)FCC and (002)HCP are identified.