Optical full-field strain measurement within a diamond anvil cell

Digital image correlation computations are run on optical images of iron samples within a diamond anvil cell to obtain in-plane strain components at the surface of the sample up to 17 GPa. The α-Fe → ε-Fe transition onset pressure and phase coexistence pressure domain can be identified from the evolution of the surface average of strain components. Strain fields exhibit localizations for both direct and reverse transition; they coincide with the approximate boundary locations of reversion variants inside the microstructure of a single crystal sample. The so-called DICDAC (Digital Image Correlation within a Diamond Anvil Cell) setup is then a suitable tool for the investigation of phase transformations strains under pressure. In addition, specific volumes that are deduced from strain out of the transition pressure domains agree within ΔV/V = 0.4% with the equation of state data from the literature.

Evaluation and application of a new scintillator-based heat-resistant back-scattered electron detector during heat treatment in the scanning electron microscope

A new high-temperature detector dedicated to the collection of backscattered electrons is used in combination with heating stages up to 1050°C, in high-vacuum and low-vacuum modes in order to evaluate its possibilities through signal-to-noise ration measurements and different applications. Four examples of material transformations occurring at high temperature are herein reported: grain growth during annealing of a rolled platinum foil, recrystallisation of a multiphased alloy, oxidation of a Ni-based alloy and complex phase transformations occurring during the annealing of an Al-Si coated boron steel. The detector could be potentially adapted to any type of SEM and it offers good opportunities to perform high-temperature experiments in various atmospheres.

In Situ High-Temperature EBSD and 3D Phase Field Studies of the Austenite-Ferrite Transformation in a Medium Mn Steel

In this research, in situ high-temperature electron backscattered diffraction (EBSD) mapping is applied to record and analyze the migration of the α/γ interfaces during cyclic austenite-ferrite phase transformations in a medium manganese steel. The experimental study is supplemented with related 3D phase field (PF) simulations to better understand the 2D EBSD observations in the context of the 3D transformation events taking place below the surface. The in situ EBSD observations and PF simulations show an overall transformation behavior qualitatively similar to that measured in dilatometry. The behavior and kinetics of individual austenite-ferrite interfaces during the transformation is found to have a wide scatter around the average interface behavior deduced on the basis of the dilatometric measurements. The trajectories of selected characteristic interfaces are analyzed in detail and yield insight into the effect of local conditions in the vicinity of interfaces on their motion, as well as the misguiding effects of 2D observations of processes taking place in 3D.

Automatic crystallographic characterization in a transmission electron microscope: applications to twinning induced plasticity steels and Al thin films

A new automated crystallographic orientation mapping tool in a transmission electron microscope technique, which is based on pattern matching between every acquired electron diffraction pattern and precalculated templates, has been used for the microstructural characterization of nondeformed and deformed aluminum thin films and twinning-induced plasticity steels. The increased spatial resolution and the use of electron diffraction patterns rather than Kikuchi lines make this tool very appropriate to characterize fine grained and deformed microstructures.