Professor Wolfgang Pantleon

Technical University of Denmark Department of Mechanical Engineering

Monitoring subgrain dynamics during plastic deformation by high resolution reciprocal space mapping

Quantitative information about dislocation structures in individual grains in the bulk of macroscopic specimens is gained by reciprocal space mapping with high resolution. In three dimensional reciprocal space maps of tensile deformed copper, individual, almost dislocation-free subgrains are identified from high-intensity peaks and distinguished by their unique combination of orientation and elastic strain; dislocation walls manifest themselves as smooth cloud of lower intensity. The elastic strain varies only slightly within each subgrain, but significantly between different subgrains. In average, subgrains experience backward strains, whereas dislocations walls are strained in forward direction. Based on these observations, the classical composite model is revised in accordance with the experimental findings.

Furthermore, subgrain dynamics can be followed in-situ during varying loading conditions by high resolution reciprocal space mapping: During uninterrupted tensile deformation, formation of subgrains is observed concurrently with broadening of Bragg reflections shortly after onset of plastic deformation. The emergence of dislocation-free regions proofs irrefutably that ordered dislocation structures develop during tensile deformation. When changing the tensile direction after pre- deformation in tension, two distinct stages in the mechanical transient can be identified. During the initial stage, the number of resolved subgrains changes only slightly while their elastic stresses are altered significantly. In case of perpendicular tensile axes, reversal of the radial profile asymmetry is observed and rationalized.

Professor Pantleon is an Associate Professor of DTU Mechanical Engineering Characterization and modelling of deformation-induced microstructures and work-hardening of metals; resolving deformation structures and dislocation densities by EBSD; X-ray peak profile analysis; high resolution reciprocal space mapping with synchrotron radiation; effect of extreme and changing loading conditions, strain path changes, fatigue; materials for fusion reactors and thermal stability