scholarly journals The electronic origins of the “rare earth” texture effect in magnesium alloys

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Reza Mahjoub ◽  
Nikki Stanford
Keyword(s):  
Electronic Structure ◽  
Rare Earth ◽  
Grain Boundary ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Magnesium Alloys ◽  
Ab Initio Simulations ◽  
Texture Effect ◽  
Complex Boundaries ◽  
Re Elements

AbstractAlthough magnesium alloys are lightweight, recyclable and relatively cheap, they suffer from poor ductility. This can be improved by the addition of rare earth (RE) elements, and this is now a well-established criterion for wrought alloy design. It is notable that this behavior is largely restricted to the lanthanides, but no hypothesis is yet available to explain why other elements do not have the same effect. To answer this question, ab initio simulations of crystallographically complex boundaries have been undertaken to examine the electronic origin of the RE effect. While the electronic structure provided strong bonding between the RE elements and their Mg surroundings, local disruption in atomic arrangement at the grain boundaries was found to modify this effect. This work shows quantifiable changes in electronic structure of solutes resulting from grain boundary crystallography, and is suggested to be a contributing factor to the RE texture effect.

scholarly journals The electronic origins of the “rare earth” texture effect in magnesium alloys

2021 ◽  
Author(s):  
Reza Mahjoub ◽  
Nikki Stanford
Keyword(s):  
Electronic Structure ◽  
Rare Earth ◽  
Grain Boundary ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Magnesium Alloys ◽  
Ab Initio Simulations ◽  
Texture Effect ◽  
Complex Boundaries ◽  
Re Elements

Abstract Although magnesium alloys are lightweight, recyclable and relatively cheap, they suffer from poor ductility. This can be improved by the addition of rare earth (RE) elements, and this is now a well-established criterion for wrought alloy design. It is notable that this behavior is largely restricted to the lanthanides, but no hypothesis is yet available to explain why other elements do not have the same effect. To answer this question, ab initio simulations of crystallographically complex boundaries have been undertaken to examine the electronic origin of the RE effect. While the electronic structure provided strong bonding between the RE elements and their Mg surroundings, local disruption in atomic arrangement at the grain boundaries was found to diminish this effect. This work shows quantifiable changes in electronic structure of solutes resulting from grain boundary crystallography, and is suggested to be a contributing factor to the RE texture effect.

Modification in Texture of Magnesium by the Addition of Rare Earth Elements and its Influence on Mechanical Properties

2012 ◽  
Vol 736 ◽  
pp. 307-315 ◽  
Author(s):  
Murugavel Suresh ◽  
Satyam Suwas
Keyword(s):  
Mechanical Properties ◽  
Rare Earth ◽  
Magnesium Alloys ◽  
Aluminium Alloys ◽  
Room Temperature ◽  
Main Obstacle ◽  
Rare Earth Addition ◽  
Structural Applications ◽  
Re Elements ◽  
The Relationship

Mg alloys show limited room temperature formability compared to its lightweight counterpart aluminium alloys, which is a main obstacle in using this metal for most of the structural applications. However, it is known that grain refinement and texture control are the two possibilities for the improvement of formability of magnesium alloys. Amongst the approaches attempted for the texture weakening, additions through of rare-earth (RE) elements have been found most effective. The relationship between the texture and ductility is well established. In this paper, the effect of rare earth addition on texture weakening has been summarized for various magnesium alloys under the two most common modes of deformation methods.

Development of New Types of Magnesium Alloys Containing Sr or RE Elements

2007 ◽  
Vol 561-565 ◽  
pp. 191-197 ◽  
Author(s):  
Fu Sheng Pan ◽  
Ming Bo Yang ◽  
Yan Long Ma
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Magnesium Alloys ◽  
Research Results ◽  
Microstructure And Properties ◽  
Minor Addition ◽  
Re Elements

The latest research results on new types of magnesium alloys containing strontium or rare earth elements are reviewed. Special attentions are paid to the alloying design, microstructure and properties controlling, the influence of minor addition of Sr and RE on the microstructure and properties of existing magnesium alloys. Some new types of magnesium alloys containing Sr or RE are introduced and discussed.

scholarly journals Grain Boundary Segregation of Rare-Earth Elements in Magnesium Alloys

2015 ◽  
Vol 47 (1) ◽  
pp. 522-530 ◽  
Author(s):  
Joseph D. Robson ◽  
Sarah J. Haigh ◽  
Bruce Davis ◽  
David Griffiths
Keyword(s):  
Rare Earth ◽  
Grain Boundary ◽  
Rare Earth Elements ◽  
Magnesium Alloys ◽  
Boundary Segregation ◽  
Grain Boundary Segregation

Modeling Boron Diffusion in Polycrystalline HfO2 Films

2002 ◽  
Vol 716 ◽  
Author(s):  
Chun-Li Liu
Keyword(s):  
Grain Boundary ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Concentration Profiles ◽  
Boron Diffusion ◽  
Gate Stacks ◽  
Modeling Prediction ◽  
Sims Analysis

AbstractWe present ab-initio modeling results including formation, migration, and activation energies for B diffusion through bulk and grain boundaries in polycrystalline HfO2 films. Modeling results clearly indicate that B can penetrate through a 40 Å HfO2 film via grain boundary diffusion, but not by bulk diffusion. SIMS analysis of B concentration profiles for polysilicon/HfO2/Si gate stacks after different anneals showed double B peaks at the interfaces and thus confirmed the modeling prediction.

scholarly journals Z-Contrast STEM Imaging and Ab-Initio Calculations of Grain Boundaries in SrTiO3

1999 ◽  
Vol 586 ◽  
Author(s):  
Miyoung Kim ◽  
Nigel D. Browning ◽  
Stephen J. Pennycook ◽  
Karl Sohlberg ◽  
Sokrates T. Pantelides
Keyword(s):  
Grain Boundary ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Theoretical Calculations ◽  
Intrinsic Property ◽  
Dislocation Core ◽  
Positive Temperature Coefficient ◽  
Positive Temperature ◽  
Z Contrast

ABSTRACTThe understanding of electrical properties of grain boundaries in perovskites is essential for their application to capacitors, varistors and positive-temperature coefficient resistors. The origin of the electrical activity is generally attributed to the existence of charged defects in grain boundaries, usually assumed to be impurities, which set up a double Schottky barrier as they are screened by dopants in the adjacent bulk crystal. Microscopic understanding of the origin of the grain boundary charge, however, has not been achieved. It is not known yet if the charged grain boundary states are an intrinsic property of a stoichiometric grain boundary, arise from nonstoichiometry, or are caused by impurities. Here, the relation between atomic structure and electronic properties is studied by combining experiment with ab-initio calculations. The starting structures for theoretical calculations were obtained from Z-contrast images combined with electron energy loss spectroscopy to resolve the dislocation core structures comprising the boundary. Dislocation core reconstructions are typical of all grain boundaries so far observed in this material. They avoid like-ion repulsion, and provide alternative sites for cation occupation in the grain boundaries. Optimized atomic positions are found by total energy calculations. Calculated differences in vacancy formation energies between the grain boundaries and the bulk suggest that vacancy segregation can account for the postulated grain boundary charge.

Experimental Measurement of the Local Electronic Structure of Grain Boundaries in Ni3Al

1993 ◽  
Vol 319 ◽  
Author(s):  
D.A. Muller ◽  
P.E. Batson ◽  
S. Subramanian ◽  
S. L. Sass ◽  
J. Silcox
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Bulk Material ◽  
Local Strain ◽  
Dark Field ◽  
Hole Density ◽  
Spatially Resolved ◽  
Boron Segregation ◽  
Annular Dark Field

AbstractWe have examined grain boundaries in both undoped and boron doped Ni0.76Al0.24 using electron energy loss spectroscopy (EELS), x-ray fluorescence (EDX) and annular dark field (ADF) imaging in a UHV STEM. A detailed study of a high angle grain boundary in nickel rich Ni3Al doped with 1000 ppm boron shows nickel enrichment occurring in a 5Å wide region. Boron segregation to the boundary is observed with EELS and is seen to vary along the boundary, coinciding with ADF contrast changes in the surrounding grains that may be due to local strain fields. Spatially resolved EELS of the Ni L2,3 core edge, which is sensitive to changes in the hole density in the nickel d band, shows boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. Boundary regions without boron have an electronic structure similar to that of the undoped grain boundaries where the Fermi level lies deeper in the nickel d band. In addition to studying boron segregation, EELS provides a unique opportunity to examine the changes in bonding that control the local properties of the material.

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