FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
Neutron Sciences
important processing step is recrystallization, the formation and growth of specific texture components
from a deformation substructure consisting of many dislocations. Despite years of research, a
comprehensive understanding of the characteristics of recrystallization has been elusive. Even with the
availability of the most sophisticated computers and simulation tools, a direct dislocation level simulation
of recrystallization is nearly impossible. The project seeks to exploit the unique features of the VULCAN
diffractometer at the Spallation Neutron Source (SNS) to perform in situ neutron diffraction investigation
of the kinetics of texture evolution. The texture data in conjunction with the existing advanced
microstructure evolution modeling and high-performance computing capabilities at ORNL will be used to
develop an integrated, predictive, process-modeling tool for structural materials. The tool will be used to
devise a new annealing procedure for wrought magnesium alloys by inducing and controlling the
development of unique texture components for enhancing their room temperature formability. The
successful completion of this research will lead to enhanced use of wrought magnesium sheets in
automobiles resulting in significant energy savings through weight reduction.
Mission Relevance
The project focuses on the development of lightweight materials for structural and energy applications
and is therefore of relevance to the mission of DOE’s Industrial Technology Program and Vehicle
Technology Program. It is also of interest to the Department of Defense (DoD) and the National
Aeronautics and Space Administration (NASA) because of the unique applications that the proposed
approach might generate in defense and aerospace components.
Results and Accomplishments
We have performed the initial, in situ neutron diffraction measurements of recovery and recrystallization
in Al-2Mg alloy and a commercial Mg alloy AZ31 using the engineering spectrometer, VULCAN, at
SNS in order to understand the kinetics of the processes and the evolution of texture. In Al-2Mg the
measurements clearly indicate the strengthening of Cube texture associated with recrystallization. In
AZ31, the process that occurred predominantly at the test temperature was recovery associated with
reduction in peak width. No significant difference in recovery kinetics was observed in Al-2Mg between
different texture components. However, this conclusion must be validated using optimized experiments
that will allow more efficient data collection at early times.
We have extended the existing crystal plasticity models to Hexagonal Close Packed systems and also
successfully mapped microstructure and texture from experimental samples to three-dimensional
simulation domains. The crystal plasticity deformation model captures the texture evolution during
deformation plane strain compression as well as the weakening of the basal texture in the presence of
shear. An existing nucleation model based on “Excess dislocations” to explain Cube texture formation
during recrystallization in Face Centered Cubic polycrystals was used to investigate the weakening of
Cube texture during cross-rolling of aluminum.
Since the in situ recrystallization experiments are the first of their kind at SNS, we are learning as we go
along to better optimize the experimental conditions to improve the quality of our results. One such area
is in rapid specimen heating and the control of sample temperature. We have initiated activities at SNS for
exploring various specimen heating techniques which we will exploit in the second round of experiments.
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