File Name: mechanism of plastic deformation slip and twinning ppt to .zip
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In materials science, slip is the large displacement of one part of a crystal relative to another part along crystallographic planes and directions. Close-packed planes are known as slip or glide planes. A slip system describes the set of symmetrically identical slip planes and associated family of slip directions for which dislocation motion can easily occur and lead to plastic deformation.
The magnitude and direction of slip are represented by the Burgers vector. An external force makes parts of the crystal lattice glide along each other, changing the material's geometry. A critical resolved shear stress is required to initiate a slip. Slip in face centered cubic fcc crystals occurs along the close packed plane. In the diagram on the right, the specific plane and direction are and [ 1 10], respectively.
Given the permutations of the slip plane types and direction types, fcc crystals have 12 slip systems. Slip in body-centered cubic bcc crystals occurs along the plane of shortest Burgers vector as well; however, unlike fcc, there are no truly close-packed planes in the bcc crystal structure.
Thus, a slip system in bcc requires heat to activate. Some bcc materials e. Although the number of possible slip systems is much higher in bcc crystals than fcc crystals, the ductility is not necessarily higher due to increased lattice friction stresses.
In the diagram on the right the specific slip plane and direction are and [ 1 11], respectively. Slip in hexagonal close packed hcp metals is much more limited than in bcc and fcc crystal structures. The activation of other slip planes depends on various parameters, e. Since there are only 2 independent slip systems on the basal planes, for arbitrary plastic deformation additional slip or twin systems needs to be activated. This typically requires a much higher resolved shear stress and can result in the brittle behavior of some hcp polycrystals.
However, other hcp materials such as pure titanium show large amounts of ductility. This creates a total of three slip systems, depending on orientation. Other combinations are also possible. There are two types of dislocations in crystals that can induce slip - edge dislocations and screw dislocations. Edge dislocations have the direction of the Burgers vector perpendicular to the dislocation line, while screw dislocations have the direction of the Burgers vector parallel to the dislocation line.
The type of dislocations generated largely depends on the direction of the applied stress, temperature, and other factors. Screw dislocations can easily cross slip from one plane to another if the other slip plane contains the direction of the Burgers vector.
From Wikipedia, the free encyclopedia. J ; "Introduction to Dislocations", 4th ed. Mechanical properties of engineered materials. Marcel Dekker. Acta Materialia. Categories : Materials science. Hidden categories: Webarchive template wayback links.
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This article discusses the experiments, computer simulations, and theoretical models addressing the conventional and specific mechanisms of plastic deformation in nanocrystalline metallic materials. Particular attention is devoted to the competition between lattice dislocation slip and specific deformation mechanisms mediated by grain boundaries as well as its sensitivity to grain size and other parameters of nanocrystalline metallic structures. Nanocrystalline materials have outstanding mechanical properties, thus giving rise to a wide range of new applications see, e. For instance, nanocrystalline metallic materials often exhibit extremely high strength, superhardness, and good fatigue resistance desired for numerous technologies. At the same time, in most cases, ductility and fracture toughness of these materials are disappointingly low. In general, the mechanical properties of nanocrystalline metallic materials are significantly different from those of their coarse-grained counterparts. The difference is attributed to the effects of the specific structural peculiarities such as nanoscopic grain sizes and large amounts of grain boundaries on plastic flow and fracture mechanisms operating in nanocrystalline materials [1—7].
Twinning and slip are the basic plastic deformation mechanisms of polycrystalline materials. Although defects can hinder lattice dislocations. Figure presents schematic movement of atoms during plastic deformation in slip and during twinning. Page 5. Figure Schematic presentation of different. Deformation by twinning On a macroscopic scale, plastic deformation corresponds to the net movement of motion is called slip movement of dislocations.
deformation, namely slip and twinning. • Slip is the prominent mechanism of plastic deformation in metals. It involves sliding of blocks of crystal over one other.
Dislocations move on a certain crystallographic plane: slip plane Dislocations move in a certain crystallographic direction: slip direction The combination of slip direction and slip plane is called a slip system. Slip planes are normally close-packed planes Slip directions are normally close-packed directions. Results in more stress to move dislocations or cause plastic deformation :called work hardening This type of interaction also leads to dislocation multiplication which leads to more interactions and more work hardening. Common in hcp and bcc structures Limited deformation but help in plastic deformation in hcp and bcc crystals Occurs on specific twinning planes and twinning directions. Deformation at temperatures below 0.
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In materials science, slip is the large displacement of one part of a crystal relative to another part along crystallographic planes and directions. Close-packed planes are known as slip or glide planes. A slip system describes the set of symmetrically identical slip planes and associated family of slip directions for which dislocation motion can easily occur and lead to plastic deformation. The magnitude and direction of slip are represented by the Burgers vector. An external force makes parts of the crystal lattice glide along each other, changing the material's geometry.
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Deformation twinning provides a mechanism for energy dissipation in crystalline structures, with important implications on the mechanical response of carbonate biogenic materials.