Twinning in monoclinic beta-phase plutonium

Abstract

Twinning has been investigated in body-centered monoclinic beta-phase plutonium by Transmission Electron Microscopy (TEM). A triode sputtering System was used to produce single-phase thick films of room temperature stabilized beta-phase metal. General examination of the microstructure revealed a very fine grain size (~100 nm) and the presence of twins. As expected in a fine grained metal, the dislocation density was low. Morphologically the twins appeared much like annealing twins observed in many melais and alloys, however, the formation of twins may have been due to deformation, growth or transformation processes. The definitive mode of formation has not been established, although classical deformation twinning theory was used to interpret the crystallography of the observed twins. Close inspection of the twins using microdiffraction revealed the individual parent/twin orientations. Crystallographic analysis of the electron diffraction patterns showed that Type II twinning appears to predominate, with a common orientation relationship between parent and twins described as a two-fold rotation axis about the [110] shear direction (η 1). Further work is in progress to theoretically predict the complete twinning Systems for beta-phase plutonium.