期刊
ACTA MATERIALIA
卷 88, 期 -, 页码 180-189出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2014.12.053
关键词
Grain boundary structure; Grain boundary segregation; Ab initio calculations; Rhenium effect; Virtual crystal approximation
资金
- Plansee SE
- Austrian Federal Government (Bundesministerium fur Verkehr, Innovation und Technologie)
- Austrian Federal Government (Bundesministerium fur Wissenschaft, Forschung und Wirtschaft)
- COMET
We investigate grain boundaries (GBs) in W-25 at.% Re alloys with special focus on the segregation of Re to the GBs and the changes in their cohesive properties that arise therefrom. Our simulations rely on density functional theory and a mean-field approximation, the virtual crystal approximation, to model the highly alloyed system. Based on a gamma-surface approach, the geometry of a wide range of GBs, including tilt, twist and mixed GBs, is obtained. Segregation energies are found to vary strongly between different segregation sites, with the strongest segregation energy amounting to -0.75 eVs. We show that bond-order parameters are able to identify strong segregation sites based on purely geometric information only. With a thermodynamic model based on a Bragg Williams approach, the concentration of Re atoms is calculated as a function of GB character at 1913 K and compared with atom probe experiments. The segregation levels are similar, with a trend towards higher segregation levels observed in the calculations for certain misorientation angles. Finally, Re alloying is found to lead to a general increase in the work of separation of the GBs, suggesting a reduction in the tendency for intergranular fracture. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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