Both elastic fields are directly dependent on inplane. The stress field, and sliding displacement and velocity can be calculated at a boundary with a shape which is periodic. Ab show that gb sliding occurs in one gb inclined to the free surface of the sample with a. The contributions of grain boundary sliding gbs to the total strain were measured directly using atomic force microscopy. However, we found that dislocationaccommodated grain boundary sliding disgbs, rather than. The sliding distance is described in percentage of acls, where acls is the lattice parameter of the coincident site lattice csl cell along 120. Abstractgrain rotation is a wellknown phenomenon during high homologous temperature deformation and. Grain boundary sliding, ebsd examination, subgrain, creep, constant loading rate, interruption, cuofp.
Grain boundary sliding in pure and segregated bicrystals. This occurs in polycrystalline material under external stress at high homologous temperature above 0. Grainboundary sliding gbs can lead to stress concentrations at triple points and hard particles on the grain boundaries, although it is unclear whether the local stresses are sufficient to nucleate cavities 20,803 20 803. Based on laboratory experiments on samples made of fine. Pdf grain boundary sliding gbs is a shift of adjacent grains against one another. On the other hand, simulations at higher temperatures on samples with symmetric grains and only highenergy grain boundaries, suggest that sliding is governed by enhanced grain boundary diffusion coble creep.
Deformation by grain boundary sliding and slip creep. The occurrence of grainboundary sliding gbs at room temperature was demonstrated by the displacement of scribed lines across grain boundaries of deformed. The change in grain size appears to be concomitant with increased activity of independent grain boundary sliding as indicated. Within our description, stress concentration near the crack initiates grain boundary sliding which results in the formation the dipole of disclinations at triple junctions of grain boundaries. A constitutive equation for grain boundary sliding. Such a feature is utilized to model grain boundary sliding gbs, which is also an important mechanism for creep. Grain boundary sliding an overview sciencedirect topics. Grain boundary sliding in phosphorus alloyed oxygenfree. However, direct measurements of the amount grain boundary sliding have not been taken and this prevents accurate modeling of the motion within earth. Abstract a model for grain boundary sliding is developed in which sliding occurs by the movement of dislocations along, or adjacent to, the boundary by a. We find evidence that the directionally solidified alloys deform by means of grain boundary sliding, presumably accompanied by diffusion near.
Density functional theory calculations show that the correction of 2d stacking faults is triggered by the ejection of mo atoms in mirror twin boundaries, followed by the collective migrations of 1d gb. Grain boundary article about grain boundary by the free. Grain boundary sliding is a material deformation mechanism where grains slide against each other. Contrasting viscoelastic beha vior of meltfree and melt. The grain boundary sliding in polycrystals is not free at high stresses and can be accommodated by creep deformation within grains. Kassner, in fundamentals of creep in metals and alloys second edition, 2008. The accurate and efficient modeling of gb constitutive behavior and capturing all relevant phenomena remains a challenging field in materials science, see, e. Grain boundary dislocations are accumulated at the grain boundaries near the triple junctions. At temperatures above the equicohesive temperature, the grain interiors are more resistant to deformation than the grain boundaries, and the grain boundaries can sustain substantial deformation. The deformation process associated with this mechanism is referred to as granular flow. The dependence of grainboundary sliding on shear stress. In the gbs model, the grain boundary region behaves more of j 2. The creep mechanism of grain boundary sliding is also sometimes referred to as superplastic or granular flow. Crystals free fulltext incompatibility stresses and.
Grain boundary sliding as a deformation mechanism during creep. Grain boundary sliding during friction stir spot welding of an aluminum alloy a. Shibayanagib auniversity of alberta, chemical and materials engineering, 536 cme building, edmonton, ab, canada t6g 2g6 bosaka university, joining and welding research institute, osaka 5670047, japan received 26 august 2008. Equilibrium grain boundary properties, such as energy, speci. In the case of grain boundary sliding induced anelasticity, the process is usually characterized by a distribution of time constants. The sliding of olivine along the grains boundaries is an important mode of movement in the mantle. A grain boundary gb is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundary sliding during friction stir spot welding. Explicit analytic expressions of stress and lattice rotation jumps are thus derived at a planar interface in the general framework of heterogeneous anisotropic thermoelasticity with plasticity and grain boundary sliding. Grain boundary sliding in creep physics stack exchange. The behavior of adjacent materials at the boundary where they meet is an essential aspect of creating new.
In this case the deformation within the grains is nonuniform and high stress and strain are produced at the triple grain junctions. The hptprocessed samples had ultrafinegrained structures and they were tested in tension at room temperature at various strain rates in the range from 1. Implications for the nature of grainboundary sliding ian jackson a. Although the alloy shows negligible srs at strain rates of 105 s1 at room temperature, the exponent increased by one order from 0. When the time scales for diffusion and grain boundary sliding are widely separated, as in recent attenuation experiments cooper 2002. Grain boundaries are defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. Healing of planar defects in 2d materials via grain boundary sliding. This first one is a stored volume energy that acts uniformly in every portion of the affected grain that is being swept by a moving grain boundary. Grain boundary sliding is a material deformation mechanism where grains slide against each. In addition, in this modeling framework, j 2 plasticity can coexist with crystal plasticity. This article is from nature communications, volume 5.
This study investigated strainrate sensitivity srs in an asextruded az31 magnesium mg alloy with grain size of about 10 mm. Quantitative tracking of grain structure evolution in a. Contrasting viscoelastic beha vior of melt free and meltbearing olivine. Effect of dislocation and grain boundary on deformation. Pdf the problem of sliding at a nonplanar grain boundary is. Strain energy distribution in the xy plane at the center of the film. Anelasticity and grain boundary sliding proceedings of.
It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0. The grain sizedependent criterion for the dislocation emission from a semiinfinite crack tip is derived. The macroscopic deformation of the sample is caused by the rearrangement of grains as they slide past one another along grain boundaries. In order to understand the mechanism involved in gbs, a microscopic knowledge of the atomic configurations and of the movements of individual atoms is necessary. Strain localization in ultramylonitic calcite marbles by. Grain boundary sliding and its accommodation micromechanisms in a nanocrystalline specimen. During such cases, the stored energy can frequently be simplified and written in scalar form. The contribution of grain boundary sliding in tensile. Ebook grain boundaries as pdf download portable document. Grain boundary sliding is a plastic deformation mechanism where crystals can slide past each other without friction and without creating significant voids as a result of diffusion. The effect of free grain boundary sliding on creep rupture processes has been investigated by anderson and rice and tvergaard 9.
Hightemperature viscoelasticity in finely grained polycrystals is commonly attributed to diffusion and grain boundary sliding cooper 2002. Nonuniform grain boundary sliding can induce strain and rotation incompatibilities at perfectly planar interfaces. Strain localization in ultramylonitic calcite marbles by dislocation creepaccommodated grain boundary sliding. A grain boundary gb is an interesting example of an interface in which many complex mechanical phenomenasuch as gb slidingmay contribute to the interface behavior, see 11, 12. Morris b a resear ch sc hool of earth sciences, a ustralian national univer sity,canberr a, c t alia. Modelling grain boundary sliding from first principles.
As a result, grain boundary sliding depends on the misorientation 1 or the free. Grain rotation is a wellknown phenomenon for polycrystalline materials during deformation at high homologous temperatures 1,2,3,4,5,6,7,8. The problem of sliding at a nonplanar grain boundary is considered in detail. Although grain boundary sliding gbs has been recognized as an important process during hightemperature deformation in crystalline. Pdf on grain boundary sliding and diffusional creep. Crossman and ashby 1 have given clear images of coupled grain boundary sliding and grain creep by numerical simulation. These mechanisms are illustrated in figure 117 a, b. When bicrystals are subjected to a constant shear stress parallel to the boundary plane, the grain boundary sliding velocity decreases with time14. A recent study 7 proposed that the disgbs may dominate the upper mantle flow on the. Dislocationaccommodated grain boundary sliding as the.
Grain boundary sliding is an apparently quite different phenomenon. A creep rupture model accounting for cavitation at sliding. Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in earths upper mantle. Competing grainboundary and dislocationmediated mechanisms in plastic strain recovery in nanocrystalline aluminum xiaoyan lia. The driving force for gb sliding is the gain in interlayer binding energy as the more stable phase grows at the expanse of the metastable ones. Recently, the authors reported that grain boundary sliding gbs was activated at a strain rate of free if steel 4, but the detailed mechanism remains unknown. The grain boundary sliding is simulated quasistatically, by rigidly shifting the top grain with respect to the bottom by a small specified amount along the 120 direction. Strainrate sensitivity enhanced by grainboundary sliding. Homologous temperature describes the operating temperature relative to the melting temperature of the material. Influence of grain boundary sliding and grain size on. Grain rotation mediated by grain boundary dislocations in. The activation volume v was evaluated as approximately 100b3 at high.
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