Modeling predicts the role of grain boundary structure in materials in extreme environments

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Snapshots of four representative grain boundaries (GB) at 50 ps. Regime 1, random distribution of damage throughout the spall region. Regime 2, sharp spall plane at the GB, with small voids in the non-GB spall region. Regime 3, three separation planes, one at the GB, and two on each side of the GB at a distance of ~10 nm. Regime 4, sharp separation plane at the GB, with medium-size voids in the non-GB spall region. The four distinct failure modes can be clearly observed from the plots of damage distribution as a function of Z position.

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Researchers from Materials Science in Radiation and Dynamics Extremes (MST-8) filled a knowledge gap towards predicting the total damage in metals in extreme environments as a function of grain boundary characteristics. Their findings also provide a simple physics-based criterion showing the variation in the morphology of the spall planes, which is usually not well predicted by mesoscale simulations but is observed in experiments.

Their work aids in understanding the role of grain boundaries on the dynamic response of materials, which is a crucial first step toward engineering nanocrystalline and polycrystalline materials suitable for use in extreme environments. Gaining this insight through experiment alone is not possible because of the fine spatial and temporal resolution required. Hence, atomistic modeling is useful.

In their work, the researchers performed systematic molecular dynamics simulations on 185 grain boundaries in tantalum. To reflect the diversity in the local atomic structure observed in realistic grain boundaries, their samples encompassed both ordered and disordered structures. The results reveal four distinct regimes in damage distribution and failure modes as a function of mis-orientation angle. Variation in the local atomic structure was shown not to affect the failure mode. These trends correlate with the variation in the corresponding void nucleation stress.

The results can be used to develop a damage criterion for grain boundaries in various regimes that can then be used in mesoscale simulations of polycrystalline metals.

Funding and mission

The work, which leveraged the Laboratory’s expertise in materials modeling and its Institutional Computing Program, was supported by the DOE/NNSA ASC Physics and Engineering Models subprogram (LANL Program Manager Cathy Plesko, acting) from within the Materials project (LANL Project Leader D.J. Luscher). The research supports the Laboratory’s Nuclear Deterrence mission area and the Materials for the Future capability pillar, in particular the Defects and Interfaces science theme.

Reference: J. Chen and S.J. Fensin. “Associating damage nucleation and distribution with grain boundary characteristics in Ta.” Scripta Materialia 187 (2020). https://doi.org/10.1016/j.scriptamat.2020.06.035

Technical contact: Saryu Fensin