Papers by Author: S.R. Dey

Abstract: Thick (up to 5 mm) Ni electrodeposits were produced by the pulsed electrodeposition (PED) technique. The PED-Ni was investigated in planar and cross-sections using high resolution scanning electron microscopy. Grain size and local texture were studied by electron backscatter diffraction. Thermal stability and grain growth behaviour were investigated using in-situ annealing in the transmission electron microscope. It is observed that columnar grains are present in the material and that the orientation of grains is not uniform. Textures and in-situ annealing behaviour are compared to previous data on nanocrystalline PED-Ni and Ni-Fe, where a subgrain coalescence model adopted from recrystallization is used to describe the occurrence of abnormal grain growth upon annealing and where twinning was found to be responsible for the texture development.

Abstract: The orientations of the inherited tetragonal (resp. cubic) variants are calculated from the parent hcp orientation in the case of a strict orientation relation. The numbering of the variants is proposed, as well as the misorientations between them. Conversely, a method for calculating the parent hcp orientation from a sufficient number of inherited variants is proposed. It is based on orientation correlating and orientation averaging, and it is particularly useful when the inherited variants are not exactly related to the parent orientation by a strict orientation relation or when the orientations of the inherited volumes slightly vary at different locations of the variant. The method is illustrated by considering the a to g phase transformation taking place in TiAl-based alloys

Abstract: An original approach based on semi-automatic treatment of Kikuchi patterns collected by Transmission Electron Microscopy is used to analyse the a2 an g variant distributions in a quaternary TiAl-based alloy (Ti-48at.%Al-2%Cr-2%Nb), with two lamellar microstructures of different fineness. Statistic data analysis shows that neither g variant orientations nor interface misorientations are randomly distributed within a given grain. The largest deviation from randomness is observed for the coarser microstructure. We also pointed out the presence of g|g subboundaries between same but slightly misoriented variants, as well as the existence of some semicoherent g|g twins accommodated by dislocation lattices. The analysis of the misorientation distributions of g|g and g|a2|g interfaces suggests that a variant selection occurs during growth and coarsening stages of the a ® a2 + g transformation process.