Bibliography: p. 132-134.
|Statement||by N. F. Fiore and C. L. Bauer.|
|Series||Progress in materials science,, v. 13, no. 2|
|Contributions||Bauer, Charles Law, joint author.|
|LC Classifications||QC1 .P884 vol. 13|
|The Physical Object|
|Number of Pages||134|
|LC Control Number||68016588|
Comprised of 10 chapters, the text includes advanced computer modeling and very high-resolution electron microscopy to help readers better understand the structure of atoms close to the core of dislocations. It shows that atomic arrangement has a significant effect on the formation of dislocations and thereby on the properties of solids. On the Interactions of Dislocations and Solute Atoms I93 Suppose that an elastic solid B occupies a cyclic space F, N times connected, which is bounded by a surface S. Let A('), Y = 1,2,3,(N- l), be a set of Cited by: Plots of dS/b against (a) GI 'G-3 bI 3/2 c 1/2 or for interaction between solute atoms and screw dislocations using Fleischer's model and (b) G[ 'G 2 +(15 b) 2 ] 2/3 c 2/3 or for interaction. solute atoms. •Using an edge dislocation in this example, the region above an edge dislocation is in compression. The region below the core is in tension. Solute atoms with dilatational strain fields will interact with these regions to cancel out strain and thus reduce the elastic strain energy.
Introduction of Y as substitutional solute will lead to, locally, strong binding of the basal plane screw dislocation to the Y atom. If one assumes that the final state of the NEB calculation presented in Fig. 6is not interacting with the dislocation, one expects this binding energy to be approximately eV per Y atom. The solute atoms in that alloy tend to segregate to the stacking faults due to chemical interaction. A simple calculation indicates that the solute atoms segregate to such a high concentration as the stacking fault energy becomes a negative value with considerable magnitude, provided that the concentration of solute atoms is in thermal. The maximum interaction energy is defined as the binding energy between dislocation and solute atom. Taking r =2 b /3 and θ =± π /2 the binding energy is given by () W L = G 2 π 1 + ν 1 − ν Δ V View chapter Purchase book. When solute and solvent atoms differ in size, local stress fields are created. Depending on their relative locations, solute atoms will either attract or repel dislocations in their vicinity.
Equation (2) is modied by the presence of solute. Specically, when a Re atom is found adjacent to the dislocation line, an extra (binding) energy has to be overcome to nucleate the next kink-pair along that dislocation segment. This is shown in Figure1, where a Re atom is . • Solutes are attracted to dislocations to reduce strain energy of the crystal. • This results in a binding energy between the solutes and the dislocations. • The dislocations must drag the solutes along unless/until they have enough energy to “break free” from the solutes. [Ashby, Shercliff, & Cebon, p. ]. The binding energy of dislocations to solute clusters forming around their cores during static or dynamic ageing was studied in Al–Mg alloys using a chemistry-specific atomistic model. The analysis provides the functional form of the binding energy–cluster size relationship, an expression required in all current models of static and DSA. dislocation core moves to a region with larger local lattice strain (not compensated by impurity). •Greater applied stress is required to initiate and continue plastic deformation than without the impurity. •Requires diffusion of solute atoms and hence T dependent. At high T, interstitial atoms can catch up to dislocations and re-pin them.