2 edition of Enhanced grain boundary sliding during reversed creep of lead. found in the catalog.
Enhanced grain boundary sliding during reversed creep of lead.
Written in English
|The Physical Object|
|Pagination||iv l., 32 p.|
|Number of Pages||32|
|LC Control Number||70650737|
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. grain boundaries affect time-dependent behaviors of crystals, including creep and stress relaxation. In the end, relation between grain boundaries and anelastic recovery is discussed. Factors that control grain boundary sliding There are two mechanistically distinct types of grain boundary sliding: Rachinger sliding and Lifshitz.
Creep Mechanism: Grain Boundary Sliding Reference: "Animation: Grain Boundary Sliding Creep", V. Gray, Swansea University, Abstract. Grain boundaries are paths for rapid solid-state diffusion in most polycrystalline materials. If a liquid phase is segregated to the grain interfaces then the diffusivity is further enhanced, in some cases by several orders of magnitude, provided that the crystal is soluble in the liquid.
1 Creep Mechanisms vis-à-vis Power Law vs. Grain Boundary Sliding in α-β Titanium Alloys for Physics Based Prognostics Amar Kumar1, Alka Srivastava1, Nita Goel1, Avi Banerjee2 and Ashok K Koul2 1Tecsis Corporation, Colonnade Road, Ottawa, ON, K2E 7L5, Canada 2Life Prediction Technologies Inc., Polytek Street, Ottawa, ON, K1J 9J1, Canada. Grain‐boundary sliding and grain interlocking of two‐phase ceramics during creep are examined on the basis of the Dryden–Kucerovsky–Wilkinson–Watt theory. That theory is .
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M.E. Kassner, in Fundamentals of Creep in Metals and Alloys (Second Edition), Grain-Boundary Sliding. Grain-boundary 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,] 20 These mechanisms are illustrated in Figure (a), (b.
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. 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 by: The roles of grain-boundary sliding (GBS) and of other creep mechanisms in creep and fine-grain superplasticity are presented in relation to a model based on the division of grains into their central “cores“ and peripheral “mantles”; GBS and its accommodation is limited to the latter, which changes with the mode of accommodation,viz by fold formation, dislocation motion in the mantle Cited by: Damage is introduced into the grain boundary structure by failure of the grain boundary facets.
Suitable relations such as creep potentials are used to relate damage parameters on a microscopic level to macroscopic quantities such as the creep strain rate and the creep by: 1. Rachinger grain boundary sliding is a characteristic of high temperature deformation in both creep when the grain size is large (d>λ) and superplasticity when the grain size is small (dgrain size and the subgrain size, analytical procedure is used to determine the rate equation for Rachinger sliding when d> by: Importance of grain boundary sliding to creep intergranular fracture is focussed.
Previous metallographic and fractographic studies of creep intergranular fracture on metal bicrystals and polycrystals are briefly reviewed in order to show the close relationship between grain boundary sliding and fracture. Deformation ledge and migration irregularity are shown to be potential sites of stress.
Then these dislocations must be accommodated at the grain boundary to continue creep deformation. Atomic force microscopy revealed the occurrence of grain boundary sliding (GBS) in the ambient-temperature creep region. Lattice rotation of 5° was observed near grain boundaries by electron backscatter diffraction pattern analyses.
The problem of sliding at a nonplanar grain boundary is considered in detail. The stress field, and sliding displacement and velocity can be calculated at a boundary with a shape which is periodic.
It is well known that the presence of non-equilibrium boundaries may lead to enhanced grain boundary diffusivity in UFG metals [19,20] and this suggests the possible occurrence of grain boundary.
This uncouples grain boundary sliding from other accommodation processes and through testing many boundaries will link behaviour to structural characteristics of the boundaries.
Similarly, diffusional creep processes may be studied on isolated boundaries under well-controlled stress gradients. The work on individual grain boundaries will be.
Hsia, D. Parks and A. Argon, Effects of grain boundary sliding on creep constrained boundary cavitation and creep deformation, Mech. of Materials (). CrossRef Google Scholar 6. In High Temperature Deformation and Fracture of Materials, Accommodation of Diffusional Creep: Grain Boundary Sliding.
In Section the constitutive equation for diffusional creep was derived from a simple cubic single crystal. In the diffusional creep of polycrystals, atoms are transported from the grain boundaries subjected to compressive stresses to those subjected to tensile.
The grain boundary sliding in polycrystals is not free at high stresses and can be accommodated by creep deformation within grains. In this case the deformation within the grains is non-uniform and high stress and strain are produced at the triple grain junctions.
Crossman and Ashby  have given clear images of coupled grain boundary sliding and grain creep by numerical simulation. sliding grain boundary in creep deformation of OFHC cop- per.
We easily understand that any irregularity on the sliding grain boundary can be a potential site of stress concentration and cracking caused by sliding during creep.
A quantitative metallographic study of the relationship between sliding and fracture of grain boundaries was first. A constitutive model is developed for grain boundary sliding (GBS) at serrated grain boundaries.
Based on a previously developed GBS model, using the dynamics of grain boundary dislocation pile-up. Grain Boundary Sliding is a material deformation mechanism where grains slide against each other. This occurs in polycrystalline material under external stress at high homologous temperature (above ~) and low strain gous temperature describes the operating temperature relative to the melting temperature of the material.
These observations suggest that the dislocation walls formed during recovery promoted the formation of micro shear bands/cooperative grain boundary sliding and thereby enhanced the ductility.
View. Grain growth 61 The creep mechanism for specimen pt25 64 The sub-microstructure of the deformation zone 74 Correlation between grain boundary structure and diffusional creep 16 Grain boundaries and helium bubble formation 86 Suggestions for further research 89 4 Conclusions 95 A Measurements of grain sizes 96 B The creep.
Delayed elastic phenomenon during high–temperature creep of polycrystalline materials is correlated with strain due to grain boundary sliding. This correlation has been used to develop a phenomenological viscoelastic model that includes the grain–size effect.
Steady-state creep due to grain boundary sliding is therefore a type of diffusion creep and the creep rate is inversely proportional to some power of the grain size. As the characteristic length of the poly-crystal, grain diameter will be related to the average diffusion path length (at least at steady-state.).
are described in which diffusion-controlled dislocation creep and/or grain boundary sliding are the dominant deformation processes in low-stress creep. It is proposed that denuded zones are formed by stress-directed grain boundary migration with the precipitates dissolving in the moving grain boundaries.Under these conditions, the dominant creep mechanism involves the motion of dislocations, largely on the easy slip system (), accommodated by grain boundary sliding (gbs).
This grain size-sensitive creep regime is characterized by a stress exponent of n=± and a grain .To heal this, grain-boundary sliding occurs.
The diffusional creep rate and the grain boundary sliding rate must be balanced if there are no voids or cracks remaining. When grain-boundary sliding can not accommodate the incompatibility, grain-boundary voids are generated, which is related to the initiation of creep fracture. Solute drag creep.