Liquid Ga Penetration along Al Grain Boundaries: Effect of External Stress and Ga Undercooling

2006 ◽  
pp. 231-234 ◽  
Author(s):  
Olga Kozlova ◽  
Alexey Rodin
Keyword(s):  
Grain Boundaries ◽  
External Stress

scholarly journals Influence of Mo Segregation at Grain Boundaries on the High Temperature Creep Behavior of Ni-Mo Alloys: An Atomistic Study

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 6966
Author(s):  
Qian Li ◽  
Jiayong Zhang ◽  
Huayuan Tang ◽  
Hongwu Zhang ◽  
Hongfei Ye ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Creep Strain ◽  
High Stress ◽  
External Stress ◽  
Creep Strain Rate ◽  
Creep Process ◽  
Boundary Slip

Based on molecular dynamics simulations, the creep behaviors of nanocrystalline Ni before and after the segregation of Mo atoms at grain boundaries are comparatively investigated with the influences of external stress, grain size, temperature, and the concentration of Mo atoms taken into consideration. The results show that the creep strain rate of nanocrystalline Ni decreases significantly after the segregation of Mo atoms at grain boundaries due to the increase of the activation energy. The creep mechanisms corresponding to low, medium, and high stress states are respectively diffusion, grain boundary slip and dislocation activities based on the analysis of stress exponent and grain size exponent for both pure Ni and segregated Ni-Mo samples. Importantly, the influence of external stress and grain size on the creep strain rate of segregated Ni-Mo samples agrees well with the classical Bird-Dorn-Mukherjee model. The results also show that segregation has little effect on the creep process dominated by lattice diffusion. However, it can effectively reduce the strain rate of the creep deformation dominated by grain boundary behaviors and dislocation activities, where the creep rate decreases when increasing the concentration of Mo atoms at grain boundaries within a certain range.

Diffusive Creep in Polycrystals

1993 ◽  
Vol 317 ◽  
Author(s):  
David B. Laks ◽  
Dimitrios Maroudas ◽  
Sokrates T. Pantelides ◽  
IBM Thomas J. Watson
Keyword(s):  
Creep Rate ◽  
Grain Boundary ◽  
Mass Transport ◽  
Grain Boundaries ◽  
Displacement Field ◽  
First Principles ◽  
External Stress ◽  
Elastic Deformations ◽  
Theory Of Plasticity ◽  
Fully Coupled

AbstractWe report quantitative mesoscopic calculations of diffusive creep in polycrystals under external stress. The analysis includes mass transport both in the grains and along the grain boundaries, fully coupled with elastic deformations in the grains and the evolution of the displacement field. We find that the net creep rate depends strongly on the details of grain boundary arrangements. The calculations represent a first step toward a comprehensive first-principles theory of plasticity.

scholarly journals Pile-up transmission and reflection of topological defects at grain boundaries in colloidal crystals

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Xin Cao ◽  
Emanuele Panizon ◽  
Andrea Vanossi ◽  
Nicola Manini ◽  
Erio Tosatti ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Driving Force ◽  
Dynamical Behavior ◽  
Colloidal Crystals ◽  
Topological Defects ◽  
External Stress ◽  
Polycrystalline Materials ◽  
Pile Up ◽  
Interstitial Defects ◽  
Transmission And Reflection

Abstract Crystalline solids typically contain large amounts of defects such as dislocations and interstitials. How they travel across grain boundaries (GBs) under external stress is crucial to understand the mechanical properties of polycrystalline materials. Here, we experimentally and theoretically investigate with single-particle resolution how the atomic structure of GBs affects the dynamics of interstitial defects driven across monolayer colloidal polycrystals. Owing to the complex inherent GB structure, we observe a rich dynamical behavior of defects near GBs. Below a critical driving force defects cannot cross GBs, resulting in their accumulation near these locations. Under certain conditions, defects are reflected at GBs, leading to their enrichment at specific regions within polycrystals. The channeling of defects within samples of specifically-designed GB structures opens up the possibility to design novel materials that are able to confine the spread of damage to certain regions.

Liquid Ga Penetration along Al Grain Boundaries: Effect of External Stress and Ga Undercooling

2006 ◽  
Vol 249 ◽  
pp. 231-234 ◽  
Author(s):  
Olga Kozlova ◽  
Alexey Rodin
Keyword(s):  
Grain Boundaries ◽  
Compressive Stress ◽  
Liquid State ◽  
Penetration Rate ◽  
External Stress ◽  
Liquid Gallium ◽  
Penetration Process ◽  
Solid Liquid

The effects of compressive stress and undercooling of Ga to liquid gallium penetration along grain boundaries (GBs) of aluminum were investigated. It was shown that the penetration rate does not change with the temperature if gallium is in liquid state. The effect of compressive stress applied to Al samples was demonstrated. The time to wetting of all aluminum GBs increased several orders of magnitude if the compressive stress was between 0.1 and 6 MPa. It was proved that solid-liquid transformation does not take place during penetration process.

Calculation of the Stress Interaction between Dislocation Pile-Ups in Neighbouring Misoriented Grains

2016 ◽  
Vol 879 ◽  
pp. 1731-1736 ◽  
Author(s):  
R. Schouwenaars ◽  
A. Ortiz ◽  
V. H. Jacobo
Keyword(s):  
Plastic Deformation ◽  
Grain Boundaries ◽  
External Stress ◽  
Dislocation Slip ◽  
Shear Stresses ◽  
Slip Systems ◽  
Dislocation Loops ◽  
Stress Concentrations ◽  
Pile Up ◽  
Schmid Factor

During the early stages of the plastic deformation of a polycrystal, dislocations can pile-up against grain boundaries. Experimental results on large-grained materials have provided excellent verification of this phenomenon. Such a pile-up may activate dislocation slip in the neighbouring grain. Whether this occurs depends on the misorientation between the grains and the resolved shear stresses in the affected grain. Several approximate criteria have been proposed to predict the occurrence of this mechanism. Here, the problem will be assessed directly by calculating the Peach-Köhler force produced by a single dislocation pile-up in one grain on all the possible slip systems in the neighbouring grain, in combination with the effect of the applied external stress as obtained through calculation of the Schmid factor. It will be seen that the problem is significantly more complex than what is generally assumed in basic explanations of the Hall-Petch effect: highly localised stress concentrations are generated for certain misorientations, which are capable of punching out small dislocation loops which may then propagate into the neighbouring grain.

scholarly journals FEATURES OF THE Σ5 AND Σ9 GRAIN BOUNDARIES MIGRATION IN BCC AND FCC METALS UNDER SHEAR LOADING – A MOLECULAR DYNAMICS STUDY

2017 ◽  
Vol 15 (2) ◽  
pp. 285
Author(s):  
Andrey I. Dmitriev ◽  
Anton Yu. Nikonov
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Molecular Dynamics Simulation ◽  
Grain Boundaries ◽  
Shear Loading ◽  
External Stress ◽  
Dynamics Simulation ◽  
Fcc Metals ◽  
Symmetrical Tilt ◽  
Fcc Metal

Molecular dynamics simulation of metallic bicrystals has been carried out to investigate the behavior of the symmetrical tilt grain boundaries under shear loading. Σ5 and Σ9 grain boundaries in Ni and α-Fe were analyzed. It is found that behavior of the defect depends not only on the structure of boundaries but also on the type of crystal lattice. In particular it is shown that under external stress the grain boundary (GB) behaves differently in the BCC and FCC metal. A comparison of the values of displacement of various types of GB due to their migration caused by shear deformation is carried out. The results can help us to understand the features of the plastic deformation development in nanoscale polycrystals under shear loading.

Morphology, Distribution and Identification of Micro-Constituents Along Grain Boundaries in Nickel-Base Alloys

1973 ◽  
Vol 31 ◽  
pp. 176-177
Author(s):  
D. E. Fornwalt ◽  
A. R. Geary ◽  
B. H. Kear
Keyword(s):  
Electron Microscope ◽  
Grain Boundaries ◽  
Volume Fraction ◽  
Rupture Life ◽  
Stress Rupture ◽  
High Volume ◽  
Precipitate Morphology ◽  
Stress Rupture Life ◽  
Nickel Base ◽  
Scanning Electron

A systematic study has been made of the effects of various heat treatments on the microstructures of several experimental high volume fraction γ’ precipitation hardened nickel-base alloys, after doping with ∼2 w/o Hf so as to improve the stress rupture life and ductility. The most significant microstructural chan§e brought about by prolonged aging at temperatures in the range 1600°-1900°F was the decoration of grain boundaries with precipitate particles.Precipitation along the grain boundaries was first detected by optical microscopy, but it was necessary to use the scanning electron microscope to reveal the details of the precipitate morphology. Figure 1(a) shows the grain boundary precipitates in relief, after partial dissolution of the surrounding γ + γ’ matrix.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

The Effect of Specimen Thickness and Probe Size on Aem Analysis of Cr-Depletion Profiles in Sensitized Stainless Steel

1982 ◽  
Vol 40 ◽  
pp. 518-519
Author(s):  
E. L. Hall
Keyword(s):  
Grain Boundaries ◽  
Boundary Region ◽  
Chromium Concentration ◽  
Foil Thickness ◽  
Specimen Thickness ◽  
Probe Size ◽  
Analytical Electron ◽  
Analytical Electron Microscope ◽  
Sensitization Process ◽  
Compositional Gradients

Sensitization in stainless steels is caused by the formation of chromium-rich M23C6 carbides at grain boundaries, which depletes the adjacent matrix and boundary region of chromium, and hence leads to rapid intergranular attack. To fully understand the sensitization process, and to test the accuracy of theories proposed to model this process, it is necessary to obtain very accurate measurements of the chromium concentration at grain boundaries in sensitized specimens. Quantitative X-ray spectroscopy in the analytical electron microscope (AEM) enables the chromium concentration profile across these boundaries to be studied directly; however, it has been shown that a strong effect of foil thickness and electron probe size may be present in the analysis of rapidly-changing compositional gradients. The goal of this work is to examine these effects.

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