A dynamical model of a crystal structure - IV. Grain boundaries

1952 ◽  
Vol 212 (1111) ◽  
pp. 576-584 ◽  
Keyword(s):  
Crystal Structure ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Large Angle ◽  
Gradual Transition ◽  
Small Angle Boundary ◽  
Pure Metals ◽  
And Diffusion ◽  
Large Angle Boundary ◽  
Dislocation Walls

Four photographs of bubble rafts are used as a basis for discussion of the structure of grain boundaries in pure metals. In these photographs one can follow the gradual transition from a small-angle boundary made up of clearly separate dislocations to a large-angle boundary where the dislocation structure is hardly recognizable. As the angle is increased, a continuous shortening of the dislocations, accompanied by the widening of a crack on the tensile side, is seen, and the process culminates in a structure which is perhaps best described in terms of local fit and misfit. The fact is also illustrated that the dislocation content of the boundary depends on the angle of the boundary, as well as on the disorientation of the crystals that it separates. If a boundary turns it must therefore gain or lose dislocations. The bearing of this on the measurement of grain-boundary energies is discussed. Other points considered concern the range of validity of calculations of the energy of dislocation walls, and slip and diffusion along grain boundaries.

Constrained Grain Boundary Diffusion In Thin Copper Films

2004 ◽  
Vol 821 ◽  
Author(s):  
Markus J. Buehler ◽  
Alexander Hartmaier ◽  
Huajian Gao
Keyword(s):  
Thin Films ◽  
Theoretical Analysis ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Atomic Scale ◽  
Diffusional Creep ◽  
Copper Films ◽  
And Diffusion

AbstractIn a recent study of diffusional creep in polycrystalline thin films deposited on substrates, we have discovered a new class of defects called the grain boundary diffusion wedges (Gao et al., Acta Mat. 47, pp. 2865-2878, 1999). These diffusion wedges are formed by stress driven mass transport between the free surface of the film and the grain boundaries during the process of substrate-constrained grain boundary diffusion. The mathematical modeling involves solution of integro-differential equations representing a strong coupling between elasticity and diffusion. The solution can be decomposed into diffusional eigenmodes reminiscent of crack-like opening displacement along the grain boundary which leads to a singular stress field at the root of the grain boundary. We find that the theoretical analysis successfully explains the difference between the mechanical behaviors of passivated and unpassivated copper films during thermal cycling on a silicon substrate. An important implication of our theoretical analysis is that dislocations with Burgers vector parallel to the interface can be nucleated at the root of the grain boundary. This is a new dislocation mechanism in thin films which contrasts to the well known Mathews-Freund-Nix mechanism of threading dislocation propagation. Recent TEM experiments at the Max Planck Institute for Metals Research have shown that, while threading dislocations dominate in passivated metal films, parallel glide dislocations begin to dominate in unpassivated copper films with thickness below 400 nm. This is consistent with our theoretical predictions. We have developed large scale molecular dynamics simulations of grain boundary diffusion wedges to clarify the nucleation mechanisms of parallel glide in thin films. Such atomic scale simulations of thin film diffusion not only show results which are consistent with both continuum theoretical and experimental studies, but also revealed the atomic processes of dislocation nucleation, climb, glide and storage in grain boundaries. The study should have far reaching implications for modeling deformation and diffusion in micro- and nanostructured materials.

Oxygen Diffusion along Symmetric [0001] Tilt Grain Boundaries in α-Alumina

2006 ◽  
Vol 317-318 ◽  
pp. 415-418 ◽  
Author(s):  
Tsubasa Nakagawa ◽  
Isao Sakaguchi ◽  
Katsuyuki Matsunaga ◽  
Takahisa Yamamoto ◽  
Hajime Haneda ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Oxygen Diffusion ◽  
Isotopic Exchange ◽  
Boundary Diffusion ◽  
Depth Profiling ◽  
Grain Boundary Diffusion ◽  
Symmetric Tilt ◽  
And Diffusion ◽  
Diffusion Properties

Grain boundary diffusion coefficients of oxygen (δDgb) at 1793K in high purity α-alumina bicrystals with Σ7{2 _ ,310}/[0001] and Σ31{7 _ ,1140}/[0001] symmetric tilt grain boundaries were measured by means of the isotopic exchange and diffusion depth profiling using SIMS. δDgb of both grain boundaries were determined to be 7.1x10-24 [m3/sec] for Σ7 grain boundary and 5.3 x10-24 [m3/sec] for Σ31 grain boundary, respectively. These results indicate that Σ values do not directly relate to grain boundary diffusion properties.

Effect of Grain Boundary State on Diffusion and Diffusion-Controlled Processes in Ultrafine-Grained Materials Processed by Severe Plastic Deformation

2015 ◽  
Vol 5 ◽  
pp. 111-126
Author(s):  
Evgeny V. Naydenkin ◽  
Galina P. Grabovetskaya ◽  
I.P. Mishin
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Grain Boundaries ◽  
Experimental Studies ◽  
Boundary State ◽  
Diffusion Controlled ◽  
Ultrafine Grained ◽  
Ultrafine Grained Materials ◽  
And Diffusion

Experimental studies on the grain boundary diffusion and processes controlled by it in the ultrafine-grained metallic materials produced by various methods of severe plastic deformation are reviewed. Correlation between the increased diffusion permeability of grain boundaries and features of recrystallization and deformation development in these materials possessing the non-equilibrium state of grain boundaries formed during severe plastic deformation in the temperature range of T < 0.35Tm is demonstrated and analyzed.

The Micro Structural Characteristic Parameters of High Grade Pipeline Steel and its Mechanical Properties

2006 ◽  
Author(s):  
Xiaoli Zhang ◽  
Chuanjing Zhuang ◽  
Lingkang Ji ◽  
Yaorong Feng ◽  
Wenzhen Zhao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Pipeline Steel ◽  
Structural Parameters ◽  
Large Angle ◽  
Lower Bainite ◽  
Granular Bainite ◽  
High Grade ◽  
Pipeline Steels

The microstructure of high grade pipeline steels, including X65, X70, X80, X100, were studied by SEM and EBSD, respectively. It was found that the microstructures of high grade pipeline steels were composed of lower bainite, granular bainite and acicular ferrite. The phases of kinds of pipeline steels were composed of Fe3C, retained austenite and ferrite. And their percentage content, grain size and its distribution were studied respectively also. These micro structural parameters were correlated to the mechanical properties of kinds of pipeline steels. Furthermore, all kinds of angles of grain boundaries were studied, and the relationship between the angles of grain boundaries and mechanical properties was obtained. It was shown that as the improving of the steel grade, the grain boundary including small angle and large angle increased. And only when grain boundary was greater than 15 degree, it was effective to the toughness behavior.

Grain Boundary Structure and Diffusion Induced Grain Boundary Migration

1991 ◽  
Vol 229 ◽  
Author(s):  
A. H. King
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Structural Models ◽  
Solute Concentration ◽  
Boundary Structure ◽  
Grain Boundary Migration ◽  
Grain Boundary Structure ◽  
And Diffusion

AbstractWe present a review of systematic studies of diffusion induced grain boundary migration (DIGM). The results are compared with structural models for the grain boundaries in order to assess the effects of structure upon DIGM. The nucleation of DIGM is also assessed in the light of grain boundary structure and it is demonstrated that changes of grain boundary solute concentration can induce large enough energy changes to drive novel grain boundary dissociation reactions.

Local Electronic Structure and Cohesion of Grain Boundaries in Ni3Al

1994 ◽  
Vol 364 ◽  
Author(s):  
D. A. Muller ◽  
S. Subramanian ◽  
S. L. Sass ◽  
J. Silcox ◽  
P. E. Batson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Cohesive Energy ◽  
Bulk Material ◽  
Large Angle ◽  
Spatially Resolved ◽  
Boron Segregation ◽  
Environmental Embrittlement ◽  
Boron Doped ◽  
Local Electronic Structure

AbstractOne of the fundamental questions concerning Ni3Al is why doping with boron improves the room temperature ductility of the polycrystalline material. Boron is thought to prevent environmental embrittlement and increase the cohesive strength of grain boundaries since it changes the fracture mode from intergranular to transgranular. This change in cohesive energy must be reflected in the bonding changes at the grain boundary which can be probed using spatially resolved electron energy loss spectroscopy (EELS). We have examined grain boundaries in both undoped and boron doped Ni0.76Al0.24 using EELS, EDX and ADF imaging in a UHV STEM. Ni-enrichment is seen in a 0.5–1 nm wide region at large angle grain boundaries, both in the absence and presence of B. EELS shows that B segregation can vary along the interface. The Ni L2, 3 core edge fine structure which is sensitive to the filling of the Ni d-band, shows only the boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. These results demonstrate that boron segregation increases the cohesive energy and hence improves the fracture resistance of the grain boundary, by making the bonding at boundaries similar to that in the bulk. The measured changes in d band filling may also affect the local solubility of hydrogen.

Primary and Secondary Grain Boundary Dislocations in Symmetric Tilt Grain Boundaries of Finite Length

1998 ◽  
Vol 538 ◽  
Author(s):  
Annamalai Lakshmanan ◽  
Alexander H. King
Keyword(s):  
Free Surface ◽  
Grain Boundary ◽  
Crystal Lattice ◽  
Grain Boundaries ◽  
Finite Length ◽  
Large Angle ◽  
Symmetric Tilt ◽  
The Creation ◽  
Meso Scale

AbstractSecondary grain boundary dislocations in large-angle grain boundaries (also called dsc-dislocations) can be described as local variations in the density of the primary (or lattice) dislocations that make up the boundary. We present a simple meso-scale simulation in which the interactions of primary dislocations with each other and with the crystal lattice produce secondary dislocations with smaller Burgers vectors and larger spacing. We use the model to explore the interactions of the primary and secondary defects with a free surface terminating the grain boundary, and demonstrate cases in which the primary dislocations dominate the interactions, forcing the secondary dislocations to increase their energy. Other cases are found, for which all of the dislocations can respond in such a way that their energy decreases. The creation of interfacial disclinations is also demonstrated.

Structure and misorientation angle distributions of (001) twist grain boundaries in Bi2Sr2Ca1Cu2Oy/Ag composite tapes processed in different oxygen partial pressures

1999 ◽  
Vol 14 (2) ◽  
pp. 349-353 ◽  
Author(s):  
Hiroki Fujii ◽  
Hiroaki Kumakura ◽  
Kazumasa Togano
Keyword(s):  
Grain Boundaries ◽  
Misorientation Angle ◽  
Small Angle ◽  
Large Angle ◽  
Amorphous Layer ◽  
High Energy ◽  
Boundary Structure ◽  
Partial Pressures ◽  
Small Angle Boundary ◽  
Twist Boundaries

We investigated the relationship between the structure and misorientation angle of (001) twist grain boundaries in Bi2Sr2Ca1Cu2Oy/Ag composite tapes processed in different oxygen partial pressures (PO2 = 0.01, 0.21, and 1 atm). Large-angle misoriented twist boundaries (>10°) essentially had no amorphous layers at the interface, and the misorientation angles of these boundaries mostly corresponded to low-energy misorientations. This large-angle misoriented boundary structure was independent of PO2. Small-angle misoriented twist boundaries (<10°), on the other hand, corresponded to high-energy misorientations and sometimes had amorphous layers at the interface. The population of the small-angle boundary with an amorphous layer was very low in the tape processed in PO2 = 1 atm. This suggests that high PO2 during the heat treatment is effective in the improvement of grain coupling, and hence, to increase critical current density.

Defect Generation and Diffusion Mechanisms in Al and Al-Cu

1998 ◽  
Vol 516 ◽  
Author(s):  
C. - L. Liu ◽  
X.-Y. Liu ◽  
L. J. Borucki
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Frenkel Pair ◽  
Generation Process ◽  
Defect Generation ◽  
Simulation Techniques ◽  
Large Numbers ◽  
Pair Generation ◽  
Diffusion Mechanisms ◽  
And Diffusion

AbstractWe describe a newly-developed defect generation mechanism, namely the grain boundary Frenkel pair (GBFP) model, and corresponding diffusion mechanisms during electromigration developed using atomic molecular statics (MS), Monte Carlo (MC), and molecular dynamics (MD) simulation techniques in Al and Al-Cu. We contend that large numbers of interstitials and vacancies exist at grain boundaries and both contribute to mass transport. Cu preferentially segregates to the interstitial sites at grain boundaries via a Frenkel pair generation process and reduces the overall grain boundary diffusivity due to the strong binding in the Al-Cu dimer. Predictions from our models are in excellent agreement with available experimental data and observations.

Effect of Thermomechanical Treatment on the Grain Boundary Structure in Pure Aluminum

1975 ◽  
Vol 33 ◽  
pp. 172-173
Author(s):  
Eswarahalli Venkatesh ◽  
L.E. Murr
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Thermomechanical Treatment ◽  
Pure Aluminum ◽  
Metals And Alloys ◽  
Boundary Structure ◽  
Air Cooling ◽  
Grain Boundary Structure ◽  
Cold Rolled ◽  
Pure Metals

In recent years, many researchers have shown great interest in understanding the structure of grain boundaries and their influence on the mechanical properties in metals and alloys. In recent years, the structure of grain boundaries and their control have been considered as a means of understanding the strengthening mechanisms in metals and alloys. There are many ways by which the grain boundary structure can be changed both in pure metals and alloys. One such means considered here is the thermomechanical treatment of pure metals.In the present work, high purity (99.9999%) aluminum sheet, mill rolled to 0.004 in. thick, is used. The as-received condition of the sample was flash-annealed at 903°K in an argon atmosphere. Batch specimens from this stock were cold rolled to 50% reduction in thickness and annealed in air at 903°K followed by either furnace cooling or air cooling to room temperature.

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