Metal structures in 4D - Science

Science

The center is organized around the two key themes of technique development and scientific investigation.  These are represented in the figure at two levels.  The upper level is concerned with development of experimental techniques and methods, which are applied at the lower level in a set of four materials science themes all involving experimental studies, modeling and theoretical development.  The overall center leader is Prof. Henning Friis Poulsen, who is assisted by five theme leaders.  The theme leaders are experienced researchers accustomed to working together as a team.  The interconnected themes represent coupled research activities focused on the broad topic of structure evolution during processing of metallic alloys.

 
Illustration of the scientific areas covered by the center

Key themes:

Technique Development 
With high energy intense X-ray sources it is possible to record diffraction information from small selected volumes within the bulk of a sample during deformation or annealing treatments.  The resolution of the existing 3DXRD microscope at Grenoble is about 5 x 5 x 50 mm3, which is useful for investigation of structure associated with grain subdivision during deformation or growth of recrystallizing grains during annealing, but too coarse to study evolution of dislocation cell structures in highly deformed materials or to capture very detailed structural information about nucleation of recrystallizing grains, for example.  A major goal of the Centre is to upgrade the spatial and time resolution of the 3DXRD microscope to more effectively probe the finer scale structures.  This will be coupled with development of methods for automating and improving the angular resolution of crystal orientation measurements using TEM methods.

Dislocation Structures
The aim of this theme is an understanding of the formation of dislocation boundaries and the interaction of dislocations with boundaries during plastic deformation. The presence of dislocation boundaries during plastic deformation will be investigated in-situ by X-ray diffraction. The shape and broadening of X-ray peaks forms a basis for developing models of the dislocation boundary structure. In combination with post mortem characterization by TEM spatial correlations in the dislocation boundary structures are identified and their stability or changes during annealing will be followed with 3DXRD.

Boundary Migration
The focus of this theme is migration of boundaries during the recrystallization process.  Existing theories of  recrystallization incorporate continuum models for boundary migration, because experimental observations of boundary migration, and the factors that affect it, in bulk have not previously been accessible.  The capabilities of the 3DXRD microscope have already provided novel insight into the recrystallization process, and further experiments will be designed to provide the information needed for formulation of mechanism-based recrystallization models.

Nano-scale Structures
The objective of this theme is to explore the possibilities of achieving the exceptional properties associated with nano-scale structures using deformation processes to create fine-scale deformation structures.  Establishment of relations between processing conditions, micro-scale structures and material properties is considered a prerequisite to understand the nano-scale regime. This research involves structural characterization and analysis by 3DXRD, TEM and mechanical testing. The relations will be extended to the nano-scale regime through high strain deformation processes, especially high pressure torsion and friction.

Multiphase Alloys
The goal of this theme is to examine possibilities for using particles as internal markers in a micortomography experiment.  This is an exploratory research avenue which offers the possibility to supplement 3DXRD microscopy results for crystal orientation, with direct observation of the deformation gradient components.  The goal of eventually coupling the 3DXRD microscope and  x-ray microtomography results would provide the entire suite of local deformation variables in a single measurement.  In addition, this theme seeks to examine opportunities to use particle dispersions as microstructural refinement agents during processing.