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Empirical construction of interatomic potentials for studies of grain boundaries and other crystal defects: Pure metals and binary alloys
A333 182 ATOMIC IN IRON
Surface Science 144 (1984) 182-195 North-Holland, Amsterdam
A N D ELECTRONIC S T R U C T U R E S OF A G R A I N WITH
M. HASHIMOTO
IMPURITY
BOUNDARY
SEGREGATION
* and Y. ISHIDA
Institute of Industrial Sciences, University of Tokyo, Minato- ku, Tokyo 106, Japan
R. Y A M A M O T O and M. D O Y A M A Department of Metallurgy and Materials Science, Universityof Tokyo, Bunkyo -ku, Tokyo 113, Japan
and T. FUJIWARA
Institute of Materials Science, University of Tsukuba, lbaraki 305, Japan Received 3 October 1983; accepted for publication 30 December 1983 We present a short review on our current investigations of the atomic and electronic structures of a grain boundary in iron. Atomic structures of grain boundaries were simulated and the local electronic densities of states were calculated in the simulated structure. When phosphorus impurity atoms segregated at the grain boundaries in iron, trigonal prismatic F e - P clusters were formed. Segregated boron atoms tended to stay at the central site of polyhedra constructed by host atoms in the grain boundaries. The non-bonding states of the iron atom at the grain boundary disappear by forming a strong bonding orbital with the orbital Of the segregated impurity atom. This bonding orbital is formed in a Fe-3d host band in the case of a boron impurity. On the other hand, the bonding orbital is formed at lower energies for the phosphorus impurity and is less-mixed with the Fe-3d host band. Non-bonding states are formed around the FegP clusters. These can give a qualitative explanation for the embrittlement of the impurity segregated grain boundary. Finally, we can explain from the viewpoint of the electronic structure why the interstitial impurity is the ,only cohesive enhancer.
196
Surface Science 144 (1984) 196-214 North-Holland, Amsterdam
EMPIRICAL C O N S T R U C T I O N OF I N T E R A T O M I C P O T E N T I A L S FOR S T U D I E S OF GRAIN B O U N D A R I E S A N D O T H E R CRYSTAL DEFECTS: P U R E M E T A L S A N D BINARY ALLOYS V. VITEK and Y. M I N O N I S H I Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA Received 15 November 1983; accepted for publication 30 December 1983
It is first argued that pair potentials are physically meaningful if they are regarded as describing interaction between atoms embedded in an environment of similar density as that for which their derivation was made. These potentials are capable of describing structural aspects of lattice defects but not the cohesive properties. Guidelines for determination of the shape of potentials and an empirical scheme for their construction in pure metals is then outlined. It is
Surface Science 144 (1984) 182-195 North-Holland, Amsterdam
A N D ELECTRONIC S T R U C T U R E S OF A G R A I N WITH
M. HASHIMOTO
IMPURITY
BOUNDARY
SEGREGATION
* and Y. ISHIDA
Institute of Industrial Sciences, University of Tokyo, Minato- ku, Tokyo 106, Japan
R. Y A M A M O T O and M. D O Y A M A Department of Metallurgy and Materials Science, Universityof Tokyo, Bunkyo -ku, Tokyo 113, Japan
and T. FUJIWARA
Institute of Materials Science, University of Tsukuba, lbaraki 305, Japan Received 3 October 1983; accepted for publication 30 December 1983 We present a short review on our current investigations of the atomic and electronic structures of a grain boundary in iron. Atomic structures of grain boundaries were simulated and the local electronic densities of states were calculated in the simulated structure. When phosphorus impurity atoms segregated at the grain boundaries in iron, trigonal prismatic F e - P clusters were formed. Segregated boron atoms tended to stay at the central site of polyhedra constructed by host atoms in the grain boundaries. The non-bonding states of the iron atom at the grain boundary disappear by forming a strong bonding orbital with the orbital Of the segregated impurity atom. This bonding orbital is formed in a Fe-3d host band in the case of a boron impurity. On the other hand, the bonding orbital is formed at lower energies for the phosphorus impurity and is less-mixed with the Fe-3d host band. Non-bonding states are formed around the FegP clusters. These can give a qualitative explanation for the embrittlement of the impurity segregated grain boundary. Finally, we can explain from the viewpoint of the electronic structure why the interstitial impurity is the ,only cohesive enhancer.
196
Surface Science 144 (1984) 196-214 North-Holland, Amsterdam
EMPIRICAL C O N S T R U C T I O N OF I N T E R A T O M I C P O T E N T I A L S FOR S T U D I E S OF GRAIN B O U N D A R I E S A N D O T H E R CRYSTAL DEFECTS: P U R E M E T A L S A N D BINARY ALLOYS V. VITEK and Y. M I N O N I S H I Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA Received 15 November 1983; accepted for publication 30 December 1983
It is first argued that pair potentials are physically meaningful if they are regarded as describing interaction between atoms embedded in an environment of similar density as that for which their derivation was made. These potentials are capable of describing structural aspects of lattice defects but not the cohesive properties. Guidelines for determination of the shape of potentials and an empirical scheme for their construction in pure metals is then outlined. It is