Authors: Hao Wang Masanori Kohyama Shingo Tanaka Yoshinori Shiihara
Publish Date: 2015/08/01
Volume: 50, Issue: 21, Pages: 6864-6881
Abstract
Segregation of Si and Mg at grain boundaries GBs in Al and Cu has been investigated using densityfunctional theory calculations combined with recently developed localenergy and localstress schemes The physics behind the impuritysegregation energy is effectively analyzed by the localenergy decomposition For the Sigma 9 tilt and Sigma 5 twist GBs in Al and Cu Si shows large segregationenergy gains only at tighter sites where local configuration of remarkably short Si–Al or Si–Cu bonds with high charge densities of covalentbonding features are formed leading to the localenergy stabilization as the finalstate effects On the other hand Mg shows large gains only at looser sites For Mg in the Cu GBs the formation of stable Mg–Cu bonds or Mg states at looser sites is the origin of the preferential segregation as the finalstate effects For Mg in the Al GBs however the local energies of Mg–Al bonds are not so stable at looser sites while the instability of Al atoms at looser sites in pure GBs before substitution is the origin of the preferential segregation as the initialstate effects The behaviors of Si and Mg in Al GBs are dominated by the difference in local sp bonding nature among Mg Al and Si while Si–Cu and Mg–Cu spd hybridization interactions dominate the behaviors of Si and Mg in Cu GBsWe thank Dr S Ishibashi Dr S Kr Bhattacharya Dr V Sharma Prof RZ Wang and Prof S Ogata for fruitful discussions The present study was supported by the GrandinAid for Scientific Research on Innovative Areas “Bulk Nanostructured Metals” KAKENHI 22102003 the GrandinAid for Scientific Research KAKENHI 23710107 and the Elements Strategy Initiative for Structural Materials ESISM through MEXT Japan
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