FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
Science for Extreme Environment: Advanced Materials and Interfacial Processes for Energy
05574
Understanding Microstructure-Mechanics Relationships of Advanced
Structural Materials Using High-Performance Computational Modeling
and In Situ Time-Resolved Neutron Diffraction
Wei Zhang
Project Description
Property degradation of welds in advanced materials severely limits realization of the energy benefits of
these materials at extreme service environments. A fundamental understanding of weld residual stresses,
microstructure, and properties is critical for enabling the safe, efficient, and reliable operation of welded
structures. Progress towards amelioration of weld property degradation has been slow due to the
occurrence of complex welding phenomena with different physics, length, and time scales whose
synergistic effects on weld failure remain unclear. This project aims to develop a unique capability that
will enable a fundamental understanding of weld microstructure-mechanics relationships by utilizing in
situ neutron diffraction and advanced high-performance weld modeling. The neutron diffraction will
provide time-resolved spatial mapping of microstructure and stress during testing in extreme conditions,
emulating those experienced in a harsh service environment. The measured data will be used to validate
advanced weld models. In particular, this approach of combining the advanced neutron diffraction
experiment and the weld models will be applied to study the high-temperature performance of highstrength
steel welds fabricated using friction stir welding (FSW), a newly developed advanced solid-state
welding process.
Mission Relevance
New knowledge and capabilities derived from this project will provide an improved understanding of
weld microstructure-mechanics relationships and the ability to understand failure in the welds of
advanced materials such as high-temperature, high-strength alloys. The use of advanced neutron
diffraction and high-performance computing–based weld models is a compelling example of the unique
strength of national laboratories to address the significant problem of weld property degradation. Such
knowledge is relevant to specific programs, including the DOE offices of Nuclear Energy (e.g., nextgeneration
reactors), Fossil Energy, and Energy Efficiency and Renewable Energy (e.g., computational
manufacturing initiative); the Department of Transportation’s Alternative Fuels Transportation
Infrastructure program; and the Nuclear Regulatory Commission’s Nuclear Reactor Safety Research
program.
Results and Accomplishments
This year’s effort is mainly focused on two thrust areas. The first one is the development of the nextgeneration
FSW model based on transient, three-dimensional material flow and heat transfer simulation.
This advanced model uses the dynamic mesh method, combining the benefits of both Lagrangian and
Eulerian formulations, to capture the complex material flow driven by the threaded tool. Parallel highperformance
computing is utilized to speed up the analysis. Revealed using massless inert particles, the
material is shown to experience very different thermomechanical history depending on the location.
Predicted results are consistent with experimentally measured temperature-time profiles and material flow
patterns reported in the literature, indicating the model validity. This model is essential to understanding
and tailoring weld microstructure and properties based on scientific principles. The second thrust area is
the fundamental understanding of weld residual stresses through advanced thermal-stress modeling and
neutron diffraction measurement. Weld residual stresses have a crucial effect on the performance and
integrity of welded structures such as those in advanced nuclear reactor pressure vessels. In neutron
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