Abstract and subjects
The beta -> alpha transformation in plutonium is discussed in terms of the crystallography of the two phases and the resulting topological modeling of the beta/alpha interface. There has been little microscopy work on the transformation, but it is probably martensitic. beta-Pu is monoclinic I2/m, while alpha-Pu is monoclinic P2(1)/m. alpha-Pu has been described as a hexagonal close-packed pseudostructure with AB stacking of the (0 2 0)(alpha) planes with pseudo-close-packing along [1 0 0](alpha) and two other directions. beta-Pu is less obvious, but X-ray diffraction suggests that the (1 0 3)(beta) planes, which are selected as the terrace plane, have the highest structure factor and are therefore among the closest-packed planes. Other pseudo-close-packed planes, such as {2 2 (2) over bar}(beta) and {3 2 (1) over bar}(beta), could also act as terrace planes for the transformation. The (1 0 3)(beta) planes have a pseudo-hexagonal grid of Pu atoms with AB stacking and pseudo-close-packing along [3 0 (1) over bar](beta) and two other directions. A selection of terrace planes as (0 2 0)(alpha)//(1 0 3)(beta) with disconnections along [1 0 0](alpha)//[3 0 (1) over bar](beta) provides the basis for topological modeling. The model predicts a habit plane that is similar to 6 degrees from the terrace plane. The extra Pu atoms in the beta structure (17 for every 16 in alpha) are accommodated by having 16 (1 0 3)(beta) planes transform into 17 (0 2 0)(alpha) planes at steps in the interface. Short-range interstitial diffusion of Pu atoms from beta to alpha is required for the transformation to proceed. Possible lattice invariant deformation systems are discussed. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.