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.

STEM investigation of the chemistry and bonding changes associated with the grain boundary embrittlement of Cu by Bi

1996 ◽  
Vol 54 ◽  
pp. 526-527
Author(s):  
V. J. Keast ◽  
J. Bruley ◽  
D. B. Williams
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
High Current Density ◽  
High Current ◽  
Fracture Path ◽  
Scanning Electron Micrograph ◽  
Edge Structure ◽  
X Ray ◽  
Grain Boundary Embrittlement ◽  
Electron Energy Loss

It has long been known that trace amounts of Bi can embrittle Cu after appropriate heat treatments. The Bi segregates to the grain boundaries and weakens them such that failure occurs through intergranular fracture without plastic deformation. This behavior is demonstrated in the scanning electron micrograph of a typical Cu-Bi fracture surface in Figure 1. It is known that the Bi extends for only a few atomic layers into the grains on either side of the grain boundary. This narrow segregation width was been confirmed using Energy Dispersive X-ray Spectroscopy (EDS) on a VG HB603 STEM. Figure 2 shows the ratio of Bi to Cu as the probe is stepped across the grain boundary.The segregation behavior is well understood, however it is not yet properly understood how the Bi causes embrittlement once it is at the grain boundaries. The Bi must change the bonding at the boundaries so that the boundaries become weak and hence the most likely fracture path. The Electron Energy Loss Near Edge Structure (ELNES) coupled with the small probes and high current density available in a field emission STEM can provide information about the localized electronic structure and hence bonding at grain boundaries. Previous investigations indicated that the near edge structure of Cu was altered at the grain boundaries due to the presence of Bi.

Chemistry, Bonding and Fracture of Grain Boundaries in Ni3Si

1996 ◽  
Vol 460 ◽  
Author(s):  
Shanthi Subramanian ◽  
David A. Muller ◽  
John Silcox ◽  
Stephen. L. Sass
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Electron Energy Loss Spectroscopy ◽  
Cohesive Energy ◽  
Large Angle ◽  
X Ray ◽  
Electron Energy Loss ◽  
Insight Into

ABSTRACTTo obtain insight into the effect of dopants on the bonding and cohesive energy of gram boundaries in Ll2 intermetallic compounds, the chemistry and electronic structure at grain boundaries in B-free and B-doped Ni-23 at % Si alloys were examined, with electron energy loss spectroscopy (EELS) providing information on the former and energy dispersive X-ray spectroscopy (EDX) on the latter. Ni-enrichment was seen at large angle boundaries, both in the absence and presence of B. EELS of the Ni L3 edge showed that the bonding at Ni-rich grain boundaries was similar in both undoped and doped alloys. Comparison of the Ni L3 edge recorded at the grain boundary and in the bulk suggests that reduced hybridization and weaker bonding occurs at Ni-rich grain boundaries in both doped and undoped alloys. These changes in bonding are interpreted in terms of changes in the cohesive energy of the boundaries.

Morphology and atomic structure of segregated grain boundaries in Cu-Sb

1992 ◽  
Vol 50 (1) ◽  
pp. 254-255
Author(s):  
R. W. Fonda ◽  
D. E. Luzzi
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Atomic Structure ◽  
Copper Alloys ◽  
Polycrystalline Materials ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

The properties of polycrystalline materials are strongly dependant upon the strength of internal boundaries. Segregation of solute to the grain boundaries can adversely affect this strength. In copper alloys, segregation of either bismuth or antimony to the grain boundary will embrittle the alloy by facilitating intergranular fracture. Very small quantities of bismuth in copper have long been known to cause severe grain boundary embrittlement of the alloy. The effect of antimony is much less pronounced and is observed primarily at lower temperatures. Even though moderate amounts of antimony are fully soluble in copper, concentrations down to 0.14% can cause grain boundary embrittlement.

Electron energy-loss near-edge structure - a tool for the investigation of electronic structure on the nanometre scale

2001 ◽  
Vol 203 (2) ◽  
pp. 135-175 ◽  
Author(s):  
V. J. Keast ◽  
A. J. Scott ◽  
R. Brydson ◽  
D. B. Williams ◽  
J. Bruley
Keyword(s):  
Electronic Structure ◽  
Energy Loss ◽  
Electron Energy ◽  
Edge Structure ◽  
Electron Energy Loss

Investigations on electronic structure of YMnO3 by electron energy loss spectra and first-principle calculations

2019 ◽  
Vol 34 (4) ◽  
pp. 339-344
Author(s):  
S. Wang ◽  
J. Cai ◽  
H. D. Xu ◽  
H. L. Tao ◽  
Y. Cui ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Energy Loss ◽  
Experimental Spectrum ◽  
X Ray Diffraction ◽  
Edge Structure ◽  
Transmission Electron ◽  
The Individual ◽  
Electron Energy Loss ◽  
Electron Energy Loss Spectra ◽  
Good Agreement

Crystal structure and electronic structure of YMnO3 were investigated by X-ray diffraction and transmission electron microscopy related techniques. According to the density of states (DOS), the individual interband transitions to energy loss peaks in the low energy loss spectrum were assigned. The hybridization of O 2p with Mn 3d and Y 4d analyzed by the partial DOS was critical to the ferroelectric nature of YMnO3. From the simulation of the energy loss near-edge structure, the fine structure of O K-edge was in good agreement with the experimental spectrum. The valence state of Mn (+3) in YMnO3 was determined by a comparison between experiment and calculations.

scholarly journals Atomic scale crystal field mapping of polar vortices in oxide superlattices

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sandhya Susarla ◽  
Pablo García-Fernández ◽  
Colin Ophus ◽  
Sujit Das ◽  
Pablo Aguado-Puente ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Energy Loss ◽  
Crystal Field ◽  
First Principles ◽  
Atomic Scale ◽  
First Principles Calculations ◽  
Edge Structure ◽  
Electron Energy Loss ◽  
Complex Polarization ◽  
Good Agreement

AbstractPolar vortices in oxide superlattices exhibit complex polarization topologies. Using a combination of electron energy loss near-edge structure analysis, crystal field multiplet theory, and first-principles calculations, we probe the electronic structure within such polar vortices in [(PbTiO3)16/(SrTiO3)16] superlattices at the atomic scale. The peaks in Ti $$L$$ L -edge spectra shift systematically depending on the position of the Ti4+ cations within the vortices i.e., the direction and magnitude of the local dipole. First-principles computation of the local projected density of states on the Ti $$3d$$ 3 d orbitals, together with the simulated crystal field multiplet spectra derived from first principles are in good agreement with the experiments.

Quantitative analysis of spatially resolved valence electron energy-loss spectra for electronic structure studies of grain boundaries and thin intergranular films

1995 ◽  
Vol 53 ◽  
pp. 314-315
Author(s):  
Roger H. French
Keyword(s):  
Electronic Structure ◽  
Quantitative Analysis ◽  
Spectral Line ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Electron Energy ◽  
Valence Electron ◽  
Transition Strength ◽  
Spatially Resolved ◽  
Electron Energy Loss

The spatial variation of the electronic structure at interfaces is critical to both interatomic bonding at atomically abrupt interfaces such as grain boundaries and also to the development of van der Waals (vdW) attraction forces at partially wetted interfaces. This interfacial electronic structure, as represented by the interband transition strength , can be determined by Kramers Kronig (KK) analysis of either vacuum ultraviolet (VUV) optical reflectance spectra or spatially resolved valence electron energy loss (SR-VEEL) spectra. Quantitative analysis of SR-VEELS requires accurate spectral line shapes coupled with single scattering deconvolution, convergence correction, and KK analysis. Both the energy loss functions (Fig. 1) and the interband transitions (Fig. 2) determined for α-Al2O3 using SR-VEELS compare well with the VUV results. In addition the use of the spectral line scan method, whereby typically 200 SR-VEEL spectra are acquired along a scan line of 20 nm, helps overcome many uncertainties in the data acquisition and analysis.

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