Timofey Frolov, David L. Olmsted, Mark Asta, Yuri Mishin
Structural transformations at interfaces are of profound fundamental interest as complex examples of phase transitions in low-dimensional systems. They are also of practical importance due to their impact on macroscopic mechanical, transport and thermal properties of polycrystals. To date, the studies of interfacial phase transitions have been focused primarily on "complexions" of intergranular thin films in ceramics and pre-melting transitions in metallic alloys. Little is known about grain boundary (GB) transformations in single-component metals apart from the recently found dislocation pairing transition in low-angle GBs composed of discrete dislocations. Despite decades of extensive research, no compelling evidence exists for structural transformations in high-angle GBs. Experimental observations by high-resolution transmission electron microscopy (HRTEM) are extremely difficult and much of the current knowledge about GB structures comes from computer simulations. In this paper we show that the critical impediment to observations of GB phase transformations in atomistic modeling has been rooted in inadequate simulation methodology. The proposed new methodology allows variations in atomic density inside the GB core and reveals multiple GB phases with different atomic structures. Reversible first-order transformations between the GB phases are observed by varying the temperature or injecting point defects into the GB region. Due to the presence of multiple metastable phases, GBs can absorb significant amounts of point defects created inside the material by processes such as irradiation. We propose a novel mechanism of radiation damage healing in metals which may guide further improvements in radiation resistance of metallic materials through GB engineering.
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http://arxiv.org/abs/1211.1756
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