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Title: Nanocrystalline grain boundary engineering: Increasing Sigma 3 boundary fraction in pure Ni with thermomechanical treatments

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1186763
Report Number(s):
LLNL-JRNL-658874
Journal ID: ISSN 1359-6454
DOE Contract Number:
DE-AC52-07NA27344
Resource Type:
Journal Article
Resource Relation:
Journal Name: Acta Materialia; Journal Volume: 86; Journal Issue: na
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY

Citation Formats

Bober, D B, Kumar, M, and Rupert, T J. Nanocrystalline grain boundary engineering: Increasing Sigma 3 boundary fraction in pure Ni with thermomechanical treatments. United States: N. p., 2014. Web.
Bober, D B, Kumar, M, & Rupert, T J. Nanocrystalline grain boundary engineering: Increasing Sigma 3 boundary fraction in pure Ni with thermomechanical treatments. United States.
Bober, D B, Kumar, M, and Rupert, T J. Tue . "Nanocrystalline grain boundary engineering: Increasing Sigma 3 boundary fraction in pure Ni with thermomechanical treatments". United States. doi:. https://www.osti.gov/servlets/purl/1186763.
@article{osti_1186763,
title = {Nanocrystalline grain boundary engineering: Increasing Sigma 3 boundary fraction in pure Ni with thermomechanical treatments},
author = {Bober, D B and Kumar, M and Rupert, T J},
abstractNote = {},
doi = {},
journal = {Acta Materialia},
number = na,
volume = 86,
place = {United States},
year = {Tue Aug 12 00:00:00 EDT 2014},
month = {Tue Aug 12 00:00:00 EDT 2014}
}
  • We report on the structural, temperature, and frequency dependent impedance studies of Ti doped cobalt ferrite material (CoFe{sub 1.95}Ti{sub 0.05}O{sub 4}) in comparison with the pure CoFe{sub 2}O{sub 4}. XRD and Raman spectroscopy studies confirm the inverse spinel crystallization of the materials with space group of Fd-3 m. Scanning electron microscope images shows the microcrystalline nature of the particles. Homogeneity, stoichiometry, and ionic states of the ions in the composition were confirmed by energy dispersive X-ray analysis and X-ray photoelectron spectroscopic studies. Temperature and frequency dependent real (Z′) and imaginary (Z″) part of the impedance shows the existence of relaxation processesmore » and their distribution in CoFe{sub 2}O{sub 4} and CoFe{sub 1.95}Ti{sub 0.05}O{sub 4} materials. Complex impedance spectroscopy studies at low temperatures shows that the conductivity in these materials is predominantly due to the intrinsic bulk grains. With increasing the temperature, evolution of grain boundary conduction is clearly seen through the appearance of a second semi-circle in the complex impedance plots. Room temperature total dc conductivity of both CoFe{sub 2}O{sub 4} and CoFe{sub 1.95}Ti{sub 0.05}O{sub 4} materials is found to be 5.78 × 10{sup −8} and 1.61 × 10{sup −7} S/cm, respectively. Temperature variation of dc electrical conductivity follows the Arrhenius relationship and the activation energies for CoFe{sub 2}O{sub 4} corresponding to grain (0.55 eV for CoFe{sub 2}O{sub 4}), grain boundary (0.52 eV), and total conduction (0.54 eV) are discussed. Observation of well distinguishable grain and grain boundary conductions and the low conductivity values in CoFe{sub 2}O{sub 4} and CoFe{sub 1.95}Ti{sub 0.05}O{sub 4} materials indicates that these materials are promising candidates for the high frequency applications.« less
  • First-principles simulated tensile tests have been performed on Fe with a P-segregated grain boundary to investigate the nature of the bond mobility mechanism in grain boundary embrittlement. The first site for bond breaking was the Fe-P bond, despite its high charge density. This is because the Fe-P bond exhibited the covalentlike characteristics of a localized bonding and the mobility of electrons was reduced. The breaking of the Fe-P bond accelerated the breaking of the Fe-Fe bond around the Fe-P bond because the Fe-P bond breaking affected the electron density of states of the Fe-Fe bond. Thus, P segregation enhanced themore » grain boundary embrittlement in Fe.« less
  • Abstract not provided.
  • It has been known for a long time that Y ions segregate to the grain boundaries (GBs) in polycrystalline alumina with the beneficial effects of enhanced mechanical properties and increased creep resistance. No detailed microscopic theory exists to explain this so called 'Y-effect'. We provide a quantum mechanical explanation for this effect through a series of carefully designed large-scale computations. The results of our theoretical tensile experiments show that the maximum stresses in pure crystalline {alpha}-Al{sub 2}O{sub 3}, undoped {sigma} = 3 GB, and Y-doped {sigma} = 3 GB models are, respectively 55, 31 and 39 GPa at the uni-axialmore » strains of 17%, 14% and 16% in the direction perpendicular to the GB. The participation of the Y-4d and Y-4p orbitals enhances the covalent character of the Y-O bond, making it stronger than the Al-O bond it replaces. This could be the major reason for the improved mechanical properties of Y-doped {alpha}-Al{sub 2}O{sub 3}.« less