Papers by Author: Nora Mateescu

Abstract: A focused ion beam (FIB) coupled with high resolution electron backscatter diffraction (EBSD) has emerged as a useful tool for generating crystallographic information in reasonably large volumes of microstructure. In principle, data generation is reasonably straightforward whereby the FIB is used as a high precision serial sectioning device for generating consecutive milled surfaces suitable for mapping by EBSD. The successive EBSD maps generated by serial sectioning are combined using various post-processing methods to generate crystallographic volumes of the microstructure. This paper provides an overview of the use of 3D-EBSD in the study of various phenomena associated with thermomechanical processing of both crystalline and semi-crystalline alloys and includes investigations on the crystallographic nature of microbands, void formation at particles, phase redistribution during plastic forming, and nucleation of recrystallization within various regions of the deformation microstructure.

Abstract: A typical dual-beam platform combines a focussed ion beam (FIB) microscope with a field emission gun scanning electron microscope (FEGSEM). Using this platform, it is possible to sequentially mill off > ~ 50 nm slices of a material by FIB and characterise, at high resolution, the crystallographic features of each new surface by electron backscatter diffraction (EBSD). The successive images can be combined to generate 3-D crystallographic maps of the microstructure. This paper describes various aspects of 3-D FIB tomography in the context of understanding the microstructural evolution of metals during deformation and annealing. The first part of the paper describes the influence of both metal type and milling parameters on the quality of EBSD patterns generated from a surface prepared by FIB milling. Single crystals of some face centred cubic metals were examined under varying FIB milling parameters to optimise EBSD pattern quality. It was found that pattern quality improves with increasing atomic number with the FIB milling parameters needed to be adjusted accordingly. The second part of the paper describes a useful technique for FIB milling for the reliable reconstruction of 3-D microstructures using EBSD. There is an initial procedure involving extensive milling to generate a protruding rectangular-shaped volume at the free surface. Serial sectioning is subsequently carried out on this volume. The technique was used to investigate the recrystallization behaviour of a particle-containing nickel sample, which revealed a number of features of the recrystallizing grains that are not clearly evident in 2-D EBSD micrographs.