Al Grain Boundary Embrittlement Promoted by Na Impurity: An ab initio Study

2000 ◽  
Vol 653 ◽  
Author(s):  
Guang-Hong Lu ◽  
Masanori Kohyama ◽  
Rayoichi Yamamoto
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Charge Density ◽  
First Principles ◽  
Ab Initio Study ◽  
Impurity Atoms ◽  
Metallic Bond ◽  
Tilt Grain Boundary ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

AbstractWe calculate the electronic structure of AlΣ9 tilt grain boundary with substitutional Na impurity atoms by first principles pseudopotential method. Results show that by Na segregation Al grain boundary expands and the valence charge density decreases significantly along the boundary. There is no stronger bond than metallic bond in the boundary even with Na impurity. We therefore conclude that the mechanism of Na-promoted Al grain boundary embrittlement should be one kind of ‘decohesion model’.

An ab initio Investigation on the Effects of Impurity in Aluminum Grain Boundary

2001 ◽  
Vol 699 ◽  
Author(s):  
Guang-Hong Lu ◽  
Tomoyuki Tamura ◽  
Masao Kamiko ◽  
Masanori Kohyama ◽  
Ryoichi Yamamoto
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Charge Density ◽  
Ab Initio ◽  
Mobility Model ◽  
Weak Bond ◽  
Impurity Atoms ◽  
Tilt Grain Boundary ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

AbstractThe electronic structure of AlS9 tilt grain boundary with segregated impurity atoms of Na, Ca, Si and S, respectively, has been investigated by an ab initio pseudopotential method. Na and Ca segregation causes the boundary to expand and the charge density to decrease significantly. There forms several weak bond regions. Si segregation increases the charge density between Si and the neighboring Al atom. There forms a stronger Al-Si bond that is a mixture of covalent and metallic character in the boundary. For S segregation, though there forms the stronger bond between Al and S atom, some Al-S bonds may become weaker than the former Al-Al bonds because of the charge density decrease. It is concluded that the mechanism of Na or Ca-promoted Al grain boundary embrittlement is one kind of ‘decohesion model’, that of Si is ‘bond mobility model’. It can't be decided the embrittlement mechanism by S segregation is classified into ‘bond mobility model’ or ‘decohesion model’.

Solute Segregation at Σ11(113)[110] Grain Boundary and Effect of the Segregation on Grain Boundary Cohesion in Aluminum from First Principles

2010 ◽  
Vol 654-656 ◽  
pp. 942-945 ◽  
Author(s):  
Tokuteru Uesugi ◽  
Kenji Higashi
Keyword(s):  
Free Surface ◽  
Grain Boundary ◽  
First Principles ◽  
Solute Segregation ◽  
First Principles Calculations ◽  
Symmetric Tilt ◽  
Tilt Grain Boundary ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

We investigate the energy of segregation of solute Ca at symmetric tilt grain boundary in aluminum from the first-principles calculations. As energy of segregation of Ca is negative, Ca atoms tend to segregate at the grain boundary. Furthermore, on basis of the Rice-Wang model, we study the effect of the segregation of Ca on the grain boundary embrittlement of aluminum. Our first-principles calculations of energies of segregation at grain boundary and free surface show that Ca behaves as embrittler.

Grain Boundary Embrittlement of Fe Induced by P Segregation: First-Principles Tensile Tests

2011 ◽  
Vol 409 ◽  
pp. 455-460 ◽  
Author(s):  
Motohiro Yuasa ◽  
Mamoru Mabuchi
Keyword(s):  
Tensile Strength ◽  
Grain Boundary ◽  
First Principles ◽  
Tensile Tests ◽  
Bond Breaking ◽  
Charge Densities ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

The GB embrittlement mechanism of Fe enhanced by P segregation has been investigated by first-principles tensile tests because a P atom is a famous GB embrittler in Fe. The first-principles tensile tests have been performed on Fe with two P-segregated GBs, where P atoms are located at the different sites, and with a nonsegregated GB. The tensile strength and the strain to failure in the P-segregated GBs were lower than those in the nonsegegated GB. The first bond breaking occurred at the Fe-P bond owing to the covalent-like characteristics, although the charge densities were high at the Fe-P bonds even just before the bond breaking. This premature bond breaking of Fe-P was independent of the location of the P atom.

Investigations of the Bonding Changes Associated with Grain Boundary Embrittlement

1996 ◽  
Vol 458 ◽  
Author(s):  
V. J. Keast ◽  
J. Bruley ◽  
D. B. Williams
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Edge Structure ◽  
Grain Boundary Embrittlement ◽  
Impurity Elements ◽  
Electron Energy Loss ◽  
Segregation Of Impurities ◽  
Boundary Embrittlement

ABSTRACTThe embrittlement of materials through the segregation of impurities to the grain boundaries is a common and industrially important problem. Despite considerable investigation, the mechanism by which the impurity elements cause embrittlement is not well understood. A change in the electron energy loss near edge structure (ELNES) has been observed at Cu grain boundaries containing Bi. This result provides experimental evidence that a change in the electronic structure at the grain boundary is responsible for embritdement.

Atomic simulations of GB sliding in pure and segregated bicrystals

2013 ◽  
Vol 1515 ◽  
Author(s):  
Motohiro Yuasa ◽  
Yasumasa Chino ◽  
Mamoru Mabuchi
Keyword(s):  
Molecular Dynamics ◽  
Electronic Structure ◽  
Grain Boundary ◽  
Charge Density ◽  
First Principles ◽  
Deformation Mode ◽  
Md Simulations ◽  
Bond Critical Point ◽  
First Principles Calculations ◽  
Atomic Simulations

ABSTRACTGrain boundary (GB) sliding is an important deformation mode in polycrystals, and it has been extensively investigated, for example, there are many studies on influences of the atomic geometry in the GB region. However, it is important to investigate GB sliding from the electronic structure of GB for deeper understandings of the sliding mechanisms. In the present work, we investigated the GBs sliding in pure and segregated bicrystals with classical molecular dynamics (MD) simulations and first-principles calculations. It is accepted that the sliding rate is affected by the GB energy. However, there was no correlation between the sliding rate and the GB energy in either the pure or the segregated bicrystals. First-principles calculations revealed that the sliding rate calculated by the MD simulations increases with decreasing minimum charge density at the bond critical point in the GB. This held in both the pure and segregated bicrystals. It seems that the sliding rate depends on atomic movement at the minimum charge density sites.

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