It is also shown that grain boundary sliding is a mechanism that may relax incompatibility stresses of elastic, plastic and thermal origin although the latter are not resolved on the grain boundary plane. Sliding during ambienttemperature creep in hexagonal closepacked metals using atomic force microscope tetsuya matsunaga and eiichi sato institute of space and astronautical scie nce, japan aerospace exploration agency japan 1. Real grain boundaries are even more complex because they generally have both tilt and twist components. Pdf grain boundary sliding as a significant mechanism of. However, direct measurements of the amount grain boundary sliding have not been taken and this prevents accurate modeling of the motion within earth. The authors extrapolate coble creep to room temperatures, on the basis of the presence of highly disordered grain boundaries.
This type of gbs, named pure sliding, can be considered as the motion of gbds of opposite sign generated by grain boundary sources fig. Multiscale modeling of nanocrystalline materials p. The effect of free grain boundary sliding on creep rupture processes has been investigated by anderson and rice and tvergaard 9, 14, 15. Grain boundary sliding is a probable process in plastic flow of polycrystals if there is deformation incompatibility among grains and if the necessary accommodation mechanisms for grain boundary sliding can operate see below. A new crystal plasticity model is presented to account for the effect of grain boundary sliding gbs on texture evolution during large plastic deformation of nanocrystalline materials. Grain boundary sliding can operate without intragranular slip kaibyshev 1992.
A creep rupture model accounting for cavitation at sliding. Grain boundary sliding in heterogeneous anisotropic elasticity. Coupling grain boundary motion to shear deformation john w. Mechanism for viscous grainboundary sliding nature.
Ashby the problem of sliding at a nonplanar grain boundary is considered in detail. Effects of carbon nanotubes on grain boundary sliding in. As a result, grain boundary sliding depends on the misorientation 1 or the free volume 10. Pdf the problem of sliding at a nonplanar grain boundary is considered in detail. Estimation of grain boundary sliding during ambient. Interactions between grain boundary sliding and slip. Grain boundary sliding and stress concentration during creep.
Grain boundary sliding in pure and segregated bicrystals. Grainboundary sliding is the relative translation of a pair of grains by a shear movement at their common interface. Grainboundary sliding and diffusion creep in polycrystalline solids. The creep mechanism of grain boundary sliding is also sometimes referred to as superplastic or granular flow. Grain boundary sliding is a material deformation mechanism where grains slide against each other. Goldsby, department of earth and environmental science, university of. A geometrical analysis of the connection between grain boundary sliding and intragranular plastic deformation of polycrystals is performed according to the requirements of strain compatibility.
Dislocation emission at grain boundaries together with intragranular slip and unaccommodated grain boundary sliding facilitate the nucleation of voids at boundaries and triple junctions. Homologous temperature describes the operating temperature relative to the melting temperature of the material. Dislocationaccommodated grain boundary sliding as the. 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 combination of climb and glide. However, we found that dislocationaccommodated grain boundary sliding disgbs, rather than. In any case, this approach ignores the participation of grainboundary sliding, which is often observed under these conditions. In the first model, the shear sliding model, gbs is accommodated by grains freely sliding along the boundaries in a powerlaw creeping material. In the model, 12 grain boundaries are assigned for each grain and their sliding rates are calculated using newtonian viscoplasticity. Grain boundary sliding microdisplacement measurements. Most grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new phases from the solid. Rotation of basal slip planes during tension of bicrystal, which increases the difference between shear stresses in different grains a. If creep intergranular fracture is closely related to grain boundary sliding, it would be possible that some effect of grain boundary. It is suggested that crystal deformation in the mantle, in the vicinity of grain boundaries, is controlled by the annihilation of oppositely signed dislocations that climb together in the plane of the grain boundary and involve grain boundary diffusion. Boundary sliding and grain interlocking in the creep.
Modelling grain boundary sliding from first principles. Jacers is a leading source for topquality basic science research and modeling spanning the diverse field of ceramic and glass materials science. Deformation of electrodeposited nanocrystalline nickel. The insets sho w the associated rounding of the corners of nominally he xagonal grains. Grain boundaries are 2d defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. It is shown that grain boundary sliding contributes over 60% of the total strain for materials with equiaxed grains of uniform size. Grain boundary sliding as a deformation mechanism during. 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. The mechanism underlying the grain rotation is dislocation climb at the grain boundary, rather than grain boundary sliding or diffusional creep. Grain boundary sliding an overview sciencedirect topics. Formation of residual grain boundary dislocations as a result of dislocation reactions during compatible deformation.
To describe such grain boundaries, both the tilt angle. Two models are presented for grain boundary sliding gbs displacement during creep. Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in earths upper mantle. Contrasting viscoelastic beha vior of meltfree and melt. Current belief is that grain boundaries are made up of distinct atomic arrangements.
However, we found that dislocationaccommodated grain boundary sliding. Grain boundary sliding in olivine university of minnesota. Sliding behavior of individual grain boundaries in bicrystals. Grain boundary sliding during friction stir spot welding. Grain boundary sliding as a significant mechanism of low temperature plastic deformation in ecap aluminum. 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.
Based on laboratory experiments on samples made of fine. Kinetics of grain boundary sliding and rotational deformation in nanocrystalline materials 51 fig. Deformation processes on the surface and in the bulk during superplasticity. Pdf grain boundary sliding gbs is a shift of adjacent grains against one another with a shear displacement localized in their common boundary.
The contribution of mechanical spectroscopy to understanding grain boundary sliding 3 metals in chicago discovers a large relaxation with. The sliding distance is described in percentage of acls, where acls is the lattice parameter of the coincident site lattice csl cell along 120. Ritter and seidman 11 divided defect structures at grain. Cahn a, yuri mishin b, akira suzuki b a materials science and engineering laboratory, national institute of standards and technology, gaithersburg, md 208998555, usa b department of physics and astronomy, george mason university, msn 3f3, 4400 university drive, fairfax, va 220304444, usa. When bicrystals are subjected to a constant shear stress parallel to the boundary plane, the grain boundary sliding velocity decreases with time14.
Gbs is considered as crucial for the formation of creep cavities. Relationship between grain boundary sliding and intragranular slip during superplasticity. In this article, when referring to gbs, we specifically mean a mechanism in which sliding on grain boundaries is accommodated by dislocation motion. Equilibrium grain boundary properties, such as energy, speci. 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. Stimulation and suppression of grain boundary sliding by. A coremantle model for superplasticity not controlled by grain boundary sliding is proposed. Grain boundary sliding will favor texture randomization 12 and this feature has already been observed in the stir. View grain boundary sliding research papers on academia.
The sliding of olivine along the grains boundaries is an important mode of movement in the mantle. View enhanced pdf access article on wiley online library html view download pdf for offline viewing. A recent study 7 proposed that the disgbs may dominate the upper mantle flow on the. Pdf on grain boundary sliding and diffusional creep. Figure 1a shows, in a schematic way, three possible situations for grain boundary sliding, where there is a strain.
Role of grain boundary sliding in texture evolution for. Stimulation and suppression of grain boundary sliding 441 figure 2. It is now recognized that grain boundary sliding gbs is often an important mode of deformation in polycrystalline materials. Stresses and deformation at grain boundaries royal society. The stress field, and sliding displacement and velocity can. The presented dissertation discusses an experimental and analytical investigation into the interactions between grain boundary sliding gbs and slip transmission plastic deformation mechanisms, and how these are impacted by local microstructure. The effect of intragranular slip on grain boundary sliding. It is reasonable to suppose that the numbers of gbds of opposite signs are similar. Coupling grain boundary motion to shear deformation. Accommodated grain boundary sliding and dislocation. This occurs in polycrystalline material under external stress at high homologous temperature above 0. A model for superplasticity not controlled by grain. Grain boundary sliding and dislocation climb in a model twodimensional fragment of a nanocrystalline solid. Modelling grain boundary sliding from first principles p.
Grain boundary sliding gbs is thought to be the principal driving force for the nucleation, growth, and coalescence of grain boundary cavities during compressive creep of polycrystalline ceramics. Under these conditions the strain rate due to sliding is proportional to sgrave 2 d, where sgrave is the applied stress and d is the average grain diameter. 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. It has been shown theoretically that stochastic gbs gives rise to continuous cavity nucleation and transient cavity growth and coalescence. The macroscopic deformation of the sample is caused by the rearrangement of grains as they slide past one another along grain boundaries. A grain boundary is the interface between two grains, or crystallites, in a polycrystalline material.
Grain boundary sliding is the key deformation and damage mechanism for high temperature deformation of crystalline materials impacting, thus, applications ranging from nuclear reactors to aircrafts. Grain rotation mediated by grain boundary dislocations in. 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. Dynamics of grain boundary networks in superplasticity. Identification of dislocations, grain boundary sliding and point defects with the aid of sem analysis 1 ravindra d.
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