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Title: Atomistic Simulations of Helium Clustering and Grain Boundary Reconstruction in Alpha-Iron

The accumulation and clustering of He atoms at Σ3 <110> {112} and Σ73b<110>{661} grain boundaries (GBs) in bcc Fe, as well as their effects on GB reconstruction, have been investigated using atomic-level computer simulations. The accumulation of He atoms and the evolution of the GB structure all depend on local He concentration, temperature and the original GB structure. At a local He concentration of 1%, small He clusters are formed in the Σ3 GB, accompanied by the emission of single self-interstitial Fe atoms (SIAs). At a He concentration of 5%, a large number of SIAs are emitted from He clusters in the Σ3 GB and collect at the periphery of these clusters. The SIAs eventually form <100> dislocation loops between two He clusters. It is likely that impurities may promote the formation of <100> loops and enhance their stabilities in α-Fe. At a He concentration of 10%, the large number of emitted SIAs are able to rearrange themselves, forming a new GB plane within the Σ3 GB, which results in self-healing of the GB and leads to GB migration. In contrast to the Σ3 GB, He clusters are mainly formed along the GB dislocation lines in the Σ73b, and themore » emitted SIAs accumulate at the cores of the GB dislocations, leading to the climb of the dislocations within the GB plane. As compared to bulk Fe, a higher number density of clusters form at GBs, but the average cluster size is smaller. The product of cluster density and average cluster size is roughly constant at a given He level, and is about the same in bulk and GB regions and varies linearly with the He concentration.« less
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Journal Article
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Journal Name: Acta Materialia, 82:275-286
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
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Country of Publication:
United States