scholarly journals Twinning partial multiplication at grain boundary in nanocrystalline fcc metals

2009 ◽  
Vol 95 (3) ◽  
pp. 031909 ◽  
Author(s):  
Y. T. Zhu ◽  
X. L. Wu ◽  
X. Z. Liao ◽  
J. Narayan ◽  
S. N. Mathaudhu ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Fcc Metals ◽  
Partial Multiplication

Structural and thermodynamic properties of nanocrystalline fcc metals prepared by mechanical attrition

1992 ◽  
Vol 7 (7) ◽  
pp. 1751-1761 ◽  
Author(s):  
J. Eckert ◽  
J.C. Holzer ◽  
C.E. Krill ◽  
W.L. Johnson
Keyword(s):  
Thermal Analysis ◽  
Grain Size ◽  
Melting Point ◽  
Grain Boundary ◽  
Bulk Modulus ◽  
Atomic Level ◽  
X Ray Diffraction ◽  
X Ray ◽  
Fcc Metals ◽  
Mechanical Attrition

Nanocrystalline fcc metals have been synthesized by mechanical attrition. The crystal refinement and the development of the microstructure have been investigated in detail by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The deformation process causes a decrease of the grain size of the fcc metals to 6–22 nm for the different elements. The final grain size scales with the melting point and the bulk modulus of the respective metal: the higher the melting point and the bulk modulus, the smaller the final grain size of the powder. Thus, the ultimate grain size achievable by this technique is determined by the competition between the heavy mechanical deformation introduced during milling and the recovery behavior of the metal. X-ray diffraction and thermal analysis of the nanocrystalline powders reveal that the crystal size refinement is accompanied by an increase in atomic-level strain and in the mechanically stored enthalpy in comparison to the undeformed state. The excess stored enthalpies of 10–40% of the heat of fusion exceed by far the values known for conventional deformation processes. The contributions of the atomic-level strain and the excess enthalpy of the grain boundaries to the stored enthalpies are critically assessed. The kinetics of grain growth in the nanocrystalline fcc metals are investigated by thermal analysis. The activation energy for grain boundary migration is derived from a modified Kissinger analysis, and estimates of the grain boundary enthalpy are given.

Survey of Grain Boundary Energies in Four Elemental Metals

2012 ◽  
Vol 715-716 ◽  
pp. 179-179
Author(s):  
David L. Olmsted ◽  
Elizabeth A. Holm ◽  
Stephen M. Foiles
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Energy Minimization ◽  
Boundary Energy ◽  
Atomic Scale ◽  
Energy Structure ◽  
Grain Boundary Energy ◽  
Fcc Metals ◽  
Composition And Structure ◽  
Boundary Properties

Grain boundary properties depend on both composition and structure. To test the relative contributions of composition and structure to the grain boundary energy, we calculated the energy of 388 grain boundaries in four elemental, fcc metals: Ni, Al, Au and Cu. We constructed atomic-scale bicrystals of each boundary and subjected them to a rigorous energy minimization process to determine the lowest energy structure. Typically, several thousand boundary configurations were examined for each boundary in each element.

Understanding the Threshold Conditions for Dislocation Transmission from Tilt Grain Boundaries in FCC Metals under Uniaxial Loading

2014 ◽  
Vol 553 ◽  
pp. 28-34 ◽  
Author(s):  
Nathaniel James Burbery ◽  
Raj Das ◽  
Giacomo Po ◽  
Nasr Ghoniem
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Strain Analysis ◽  
Dislocation Slip ◽  
Shear Stresses ◽  
Dislocation Dynamic ◽  
Dynamic Simulations ◽  
Fcc Metals ◽  
Grain Boundary Characteristics ◽  
Meso Scale

Plastic deformation in face-centred cubic (or ‘FCC’) metals involves multi-scale phenomena which are initiated at atomic length and time scales (on order of 1.0e-15seconds). Understanding the fundamental thresholds for plasticity at atomic and nano/meso scales requires rigorous testing, which cannot be feasibly achieved with current experimental methods. Hence, computer simulation-based investigations are extremely valuable. However, meso-scale simulations cannot yet accommodate atomically-informed grain boundary (or ‘GB’) effects and dislocation interactions. This study will provide a stress - strain analysis based on molecular dynamics simulations of a series of metastable grain boundaries with identical crystal orientations but unique grain boundary characteristics. Relationships between dislocation slip systems, resolved shear stresses and additional thermo-mechanical conditions of the system will be considered in the analysis of dislocation-grain boundary interactions, including GB penetration. This study will form the basis of new phenomenological relationships in an effort to enable accommodation of grain boundaries into meso scale dislocation dynamic simulations.

Grain boundary sites in fcc metals studied by PAC

1993 ◽  
Vol 79 (1-4) ◽  
pp. 761-764 ◽  
Author(s):  
Bin Bai ◽  
Gary S. Collins
Keyword(s):  
Grain Boundary ◽  
Fcc Metals

Modeling of dislocation–grain boundary interactions in FCC metals

2003 ◽  
Vol 323 (2-3) ◽  
pp. 281-289 ◽  
Author(s):  
M de Koning ◽  
R.J Kurtz ◽  
V.V Bulatov ◽  
C.H Henager ◽  
R.G Hoagland ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Fcc Metals

Structural Unit Models for High Angle Symmetrical Tilt Boundaries in Ordered Compounds with the Ll2 Structure

1984 ◽  
Vol 39 ◽  
Author(s):  
D. Farkas
Keyword(s):  
Grain Boundary ◽  
Structural Unit ◽  
Boundary Energy ◽  
Coordination Shell ◽  
Interatomic Potentials ◽  
Two Phase ◽  
Fcc Metals ◽  
Tilt Boundaries ◽  
Hard Sphere Models ◽  
Fcc Materials

ABSTRACTHard sphere models were used to determine densest configurations in symmetrical [100] and [110] tilt boundaries in compounds with the Ll2 structure. The minimum allowed interatomic distances used in these models were estimated from interatomic potentials and the structures of the intermetallic phases in the binary system. The structural unit model is used to analyze the possible ground states for ordering.Two different cases were analyzed corresponding to compounds with “soft” potentials (i.e. Cu3 Au) and “hard” potentials (i.e. Ni3Al). For the Cu3Au type the grain boundary structures obtained were similar to those reported by other investigators for pure fcc metals. Several boundaries were found to be a “two phase” structure, differing in composition and ordering state. This leads to a certain degree of clustering in the boundaries. The contribution of clustering to the grain boundary energy is calculated in a point approximation based on the first coordination shell.For compounds of the Ni3Al type the structures that are densest were found to be generally diffetent from the low energy configurations of boundaries in, pure fcc metals and Cu3 Au. These configurations preserve order, but are much less dense. The possibility of grain boundary “phases” that are not present in other fcc materials may constitute an explanation for the extreme GB weakness observed in Ni3Al and other Ll2 compounds with high ordering energy.

Grain Boundary Sliding during Low Temperature Creep of Ultrafine and Coarse Grained Aluminum

2012 ◽  
Vol 735 ◽  
pp. 17-21
Author(s):  
Eiichi Sato ◽  
Kaoru Ishiwata ◽  
Tetsuya Matsunaga
Keyword(s):  
Grain Boundary ◽  
Cell Structure ◽  
Grain Boundary Sliding ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Fcc Metals ◽  
Boundary Sliding ◽  
The Difference ◽  
Low Temperature Creep ◽  
Structure Lead

HCP metals show new dislocation creep at temperatures below 0.3 Tm with stresses below σ0.2, while FCC metals show it above σ0.2. In the former, grain boundaries absorb the dislocations through slip-induced grain-boundary sliding, while in the latter dislocations are accommodated by cross slip at cell walls. The difference comes from the difference in the crystal symmetry. In UFG-Al at low temperatures, it is anticipated that grains without cell structure lead creep deformation similar to CG HCP metals rather than CG Al. UFG Al specimens were fabricated by ARB method. They showed remarkable creep behavior at less than σ0.2 similary to CG HCP metals. It posseses stress exponent of about three, grain-size exponent of almost zero, and very low apparent activation energy of 20 kJ/mol, and also grain boundary sliding behavior is obserbed by AFM.

Sign in / Sign up

Export Citation Format

Share Document