Slip (materials science)

Last updated
Schematic view of slip mechanism Slip system.gif
Schematic view of slip mechanism

In materials science, slip is the large displacement of one part of a crystal relative to another part along crystallographic planes and directions. [1] Slip occurs by the passage of dislocations on close/packed planes, which are planes containing the greatest number of atoms per area and in close-packed directions (most atoms per length). 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, b.

Contents

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. [2]

Slip systems

Face centered cubic crystals

Unit cell of an fcc material. Lattice face centered cubic.svg
Unit cell of an fcc material.
Lattice configuration of the close packed slip plane in an fcc material. The arrow represents the Burgers vector in this dislocation glide system. FCC Lattice.svg
Lattice configuration of the close packed slip plane in an fcc material. The arrow represents the Burgers vector in this dislocation glide system.

Slip in face centered cubic (fcc) crystals occurs along the close packed plane. Specifically, the slip plane is of type {111}, and the direction is of type <110>. In the diagram on the right, the specific plane and direction are (111) and [110], respectively.

Given the permutations of the slip plane types and direction types, fcc crystals have 12 slip systems. [3] In the fcc lattice, the norm of the Burgers vector, b, can be calculated using the following equation: [4]

[4]

Where a is the lattice constant of the unit cell.

Body centered cubic crystals

Unit cell of a bcc material. Lattice body centered cubic.svg
Unit cell of a bcc material.
Lattice configuration of the slip plane in a bcc material. The arrow represents the Burgers vector in this dislocation glide system. BCC Lattice.JPG
Lattice configuration of the slip plane in a bcc material. The arrow represents the Burgers vector in this dislocation glide system.

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.g. α-Fe) can contain up to 48 slip systems. There are six slip planes of type {110}, each with two <111> directions (12 systems). There are 24 {123} and 12 {112} planes each with one <111> direction (36 systems, for a total of 48). 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. [3] While the {123} and {112} planes are not exactly identical in activation energy to {110}, they are so close in energy that for all intents and purposes they can be treated as identical. In the diagram on the right the specific slip plane and direction are (110) and [111], respectively. [4]

[4]

Hexagonal close packed crystals

Slip systems in zirconium alloys. b and n are the slip direction and plane, respectively, and is the rotation axis calculated in the present work, orthogonal to both the slip plane normal and slip direction. The crystal direction of the rotation axis vectors is labelled on the IPF colour key. Slip systems in zirconium alloys.png
Slip systems in zirconium alloys. 𝒃 and 𝒏 are the slip direction and plane, respectively, and 𝝎 is the rotation axis calculated in the present work, orthogonal to both the slip plane normal and slip direction. The crystal direction of the rotation axis vectors is labelled on the IPF colour key.

Slip in hexagonal close packed (hcp) metals is much more limited than in bcc and fcc crystal structures. Usually, hcp crystal structures allow slip on the densely packed basal {0001} planes along the <1120> directions. The activation of other slip planes depends on various parameters, e.g. the c/a ratio. 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. [6]

Cadmium, zinc, magnesium, titanium, and beryllium have a slip plane at {0001} and a slip direction of <1120>. This creates a total of three slip systems, depending on orientation. Other combinations are also possible. [7]

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. [2]

Slip band

A slip band formed on a ferrite grain in an aged hardened stainless steel. The slip band at the centre of the image was observed at a certain load, then the load was increased with a burst of dislocations coming out of the slip band tip as a response to the load increment. This burst of dislocations and topographic change ahead of the slip band was observed across different slip bands (see the supplementary information of the paper). image length is 10 um. S4 loaded slip band.gif
A slip band formed on a ferrite grain in an aged hardened stainless steel. The slip band at the centre of the image was observed at a certain load, then the load was increased with a burst of dislocations coming out of the slip band tip as a response to the load increment. This burst of dislocations and topographic change ahead of the slip band was observed across different slip bands (see the supplementary information of the paper). image length is 10 um.

Formation of slip bands indicates a concentrated unidirectional slip on certain planes causing a stress concentration. Typically, slip bands induce surface steps (i.e. roughness due persistent slip bands during fatigue) and a stress concentration which can be a crack nucleation site. Slip bands extend until impinged by a boundary, and the generated stress from dislocation pile-up against that boundary will either stop or transmit the operating slip. [9] [10]

Formation of slip bands under cyclic conditions is addressed as persistent slip bands (PSBs) where formation under monotonic condition is addressed as dislocation planar arrays (or simply slip-bands). [11] Slip-bands can be simply viewed as boundary sliding due to dislocation glide that lacks (the complexity of ) PSBs high plastic deformation localisation manifested by tongue- and ribbon-like extrusion. And, where PSBs normally studied with (effective) Burger’s vector aligned with extrusion plane because PSB extends across the grain and exacerbate during fatigue; [12] monotonic slip-band has a Burger’s vector for propagation and another for plane extrusions both controlled by the conditions at the tip.

Identification of slip activity

The main methods to identify the active slip system involve either slip trace analysis of single crystals [13] [14] or polycrystals, [15] [8] using diffraction techniques such as neutron diffraction [16] and high angular resolution electron backscatter diffraction elastic strain analysis, [17] or Transmission electron microscopy diffraction imaging of dislocations. [18]

In slip trace analysis, only the slip plane is measured, and the slip direction is inferred. In zirconium, for example, this enables the identification of slip activity on a basal, prism, or 1st/2nd order pyramidal plane. In the case of a 1st-order pyramidal plane trace, the slip could be in either 〈𝑎〉 or 〈𝑐 + 𝑎〉 directions; slip trace analysis cannot discriminate between these. [5]

Diffraction-based studies measure the residual dislocation content instead of the slipped dislocations, which is only a good approximation for systems that accumulate networks of geometrically necessary dislocations, such as Face-centred cubic polycrystals. [19] In low-symmetry crystals such as hexagonal zirconium, there could be regions of the predominantly single slip where geometrically necessary dislocations may not necessarily accumulate. [20] Residual dislocation content does not distinguish between glissile and sessile dislocations. Glissile dislocations contribute to slip and hardening, but sessile dislocations contribute only to latent hardening. [5]

Diffraction methods cannot generally resolve the slip plane of a residual dislocation. For example, in Zr, the screw components of 〈𝑎〉 dislocations could slip on prismatic, basal, or 1st-order pyramidal planes. Similarly, 〈𝑐 + 𝑎〉 screw dislocations could slip on either 1st or 2nd order pyramidal planes. [5]

See also

Related Research Articles

<span class="mw-page-title-main">Plasticity (physics)</span> Non-reversible deformation of a solid material in response to applied forces

In physics and materials science, plasticity is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself. In engineering, the transition from elastic behavior to plastic behavior is known as yielding.

<span class="mw-page-title-main">Dislocation</span> Linear crystallographic defect or irregularity

In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to slide over each other at low stress levels and is known as glide or slip. The crystalline order is restored on either side of a glide dislocation but the atoms on one side have moved by one position. The crystalline order is not fully restored with a partial dislocation. A dislocation defines the boundary between slipped and unslipped regions of material and as a result, must either form a complete loop, intersect other dislocations or defects, or extend to the edges of the crystal. A dislocation can be characterised by the distance and direction of movement it causes to atoms which is defined by the Burgers vector. Plastic deformation of a material occurs by the creation and movement of many dislocations. The number and arrangement of dislocations influences many of the properties of materials.

<span class="mw-page-title-main">Electron backscatter diffraction</span> Scanning electron microscopy technique

Electron backscatter diffraction (EBSD) is a scanning electron microscopy (SEM) technique used to study the crystallographic structure of materials. EBSD is carried out in a scanning electron microscope equipped with an EBSD detector comprising at least a phosphorescent screen, a compact lens and a low-light camera. In the microscope an incident beam of electrons hits a tilted sample. As backscattered electrons leave the sample, they interact with the atoms and are both elastically diffracted and lose energy, leaving the sample at various scattering angles before reaching the phosphor screen forming Kikuchi patterns (EBSPs). The EBSD spatial resolution depends on many factors, including the nature of the material under study and the sample preparation. They can be indexed to provide information about the material's grain structure, grain orientation, and phase at the micro-scale. EBSD is used for impurities and defect studies, plastic deformation, and statistical analysis for average misorientation, grain size, and crystallographic texture. EBSD can also be combined with energy-dispersive X-ray spectroscopy (EDS), cathodoluminescence (CL), and wavelength-dispersive X-ray spectroscopy (WDS) for advanced phase identification and materials discovery.

<span class="mw-page-title-main">Crystal twinning</span> Two separate crystals sharing some of the same crystal lattice points in a symmetrical manner

Crystal twinning occurs when two or more adjacent crystals of the same mineral are oriented so that they share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals that are tightly bonded to each other. The surface along which the lattice points are shared in twinned crystals is called a composition surface or twin plane.

<span class="mw-page-title-main">Superalloy</span> Alloy with higher durability than normal metals

A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Key characteristics of a superalloy include mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance.

<span class="mw-page-title-main">Cottrell atmosphere</span> Concept in materials science

In materials science, the concept of the Cottrell atmosphere was introduced by A. H. Cottrell and B. A. Bilby in 1949 to explain how dislocations are pinned in some metals by boron, carbon, or nitrogen interstitials.

<span class="mw-page-title-main">Zirconium alloys</span> Zircaloy family

Zirconium alloys are solid solutions of zirconium or other metals, a common subgroup having the trade mark Zircaloy. Zirconium has very low absorption cross-section of thermal neutrons, high hardness, ductility and corrosion resistance. One of the main uses of zirconium alloys is in nuclear technology, as cladding of fuel rods in nuclear reactors, especially water reactors. A typical composition of nuclear-grade zirconium alloys is more than 95 weight percent zirconium and less than 2% of tin, niobium, iron, chromium, nickel and other metals, which are added to improve mechanical properties and corrosion resistance.

<span class="mw-page-title-main">Critical resolved shear stress</span> Component of shear stress necessary to initiate slip in a crystal

In materials science, critical resolved shear stress (CRSS) is the component of shear stress, resolved in the direction of slip, necessary to initiate slip in a grain. Resolved shear stress (RSS) is the shear component of an applied tensile or compressive stress resolved along a slip plane that is other than perpendicular or parallel to the stress axis. The RSS is related to the applied stress by a geometrical factor, m, typically the Schmid factor:

<span class="mw-page-title-main">Shear band</span>

A shear band is a narrow zone of intense shearing strain, usually of plastic nature, developing during severe deformation of ductile materials. As an example, a soil specimen is shown in Fig. 1, after an axialsymmetric compression test. Initially the sample was cylindrical in shape and, since symmetry was tried to be preserved during the test, the cylindrical shape was maintained for a while during the test and the deformation was homogeneous, but at extreme loading two X-shaped shear bands had formed and the subsequent deformation was strongly localized.

Severe plastic deformation (SPD) is a generic term describing a group of metalworking techniques involving very large strains typically involving a complex stress state or high shear, resulting in a high defect density and equiaxed "ultrafine" grain (UFG) size or nanocrystalline (NC) structure.

In materials science, the yield strength anomaly refers to materials wherein the yield strength increases with temperature. For the majority of materials, the yield strength decreases with increasing temperature. In metals, this decrease in yield strength is due to the thermal activation of dislocation motion, resulting in easier plastic deformation at higher temperatures.

<span class="mw-page-title-main">Stacking fault</span>

In crystallography, a stacking fault is a planar defect that can occur in crystalline materials. Crystalline materials form repeating patterns of layers of atoms. Errors can occur in the sequence of these layers and are known as stacking faults. Stacking faults are in a higher energy state which is quantified by the formation enthalpy per unit area called the stacking-fault energy. Stacking faults can arise during crystal growth or from plastic deformation. In addition, dislocations in low stacking-fault energy materials typically dissociate into an extended dislocation, which is a stacking fault bounded by partial dislocations.

Geometrically necessary dislocations are like-signed dislocations needed to accommodate for plastic bending in a crystalline material. They are present when a material's plastic deformation is accompanied by internal plastic strain gradients. They are in contrast to statistically stored dislocations, with statistics of equal positive and negative signs, which arise during plastic flow from multiplication processes like the Frank-Read source.

Dislocation avalanches are rapid discrete events during plastic deformation, in which defects are reorganized collectively. This intermittent flow behavior has been observed in microcrystals, whereas macroscopic plasticity appears as a smooth process. Intermittent plastic flow has been observed in several different systems. In AlMg Alloys, interaction between solute and dislocations can cause sudden jump during dynamic strain aging. In metallic glass, it can be observed via shear banding with stress localization; and single crystal plasticity, it shows up as slip burst. However, analysis of the events with orders-magnitude difference in sizes with different crystallographic structure reveals power-law scaling between the number of events and their magnitude, or scale-free flow.

<span class="mw-page-title-main">Cross slip</span> Movement of a screw dislocation between crystallographic planes

In materials science, cross slip is the process by which a screw dislocation moves from one slip plane to another due to local stresses. It allows non-planar movement of screw dislocations. Non-planar movement of edge dislocations is achieved through climb.

<span class="mw-page-title-main">Ben Britton</span> British materials scientist and engineer

Thomas Benjamin Britton is a materials scientist and engineer based at The University of British Columbia. He is a specialist in micromechanics, electron microscopy and crystal plasticity. In 2014 he was awarded the Silver Medal of the Institute of Materials, Minerals and Mining (IOM3), a society of which he then became a Fellow in 2016.

Crystal plasticity is a mesoscale computational technique that takes into account crystallographic anisotropy in modelling the mechanical behaviour of polycrystalline materials. The technique has typically been used to study deformation through the process of slip, however, there are some flavors of crystal plasticity that can incorporate other deformation mechanisms like twinning and phase transformations. Crystal plasticity is used to obtain the relationship between stress and strain that also captures the underlying physics at the crystal level. Hence, it can be used to predict not just the stress-strain response of a material, but also the texture evolution, micromechanical field distributions, and regions of strain localisation. The two widely used formulations of crystal plasticity are the one based on the finite element method known as Crystal Plasticity Finite Element Method (CPFEM), which is developed based on the finite strain formulation for the mechanics, and a spectral formulation which is more computationally efficient due to the fast Fourier transform, but is based on the small strain formulation for the mechanics.

<span class="mw-page-title-main">Slip bands in metals</span> Deformation mechanism in crystallines

Slip bands or stretcher-strain marks are localized bands of plastic deformation in metals experiencing stresses. Formation of slip bands indicates a concentrated unidirectional slip on certain planes causing a stress concentration. Typically, slip bands induce surface steps and a stress concentration which can be a crack nucleation site. Slip bands extend until impinged by a boundary, and the generated stress from dislocations pile-up against that boundary will either stop or transmit the operating slip depending on its (mis)orientation.

Angus J Wilkinson is a professor of materials science based at University of Oxford. He is a specialist in micromechanics, electron microscopy and crystal plasticity. He assists in overseeing the MicroMechanics group while focusing on the fundamentals of material deformation. He developed the HR-EBSD method for mapping stress and dislocation density at high spatial resolution used at the micron scale in mechanical testing and micro-cantilevers to extract data on mechanical properties that are relevant to materials engineering.

<span class="mw-page-title-main">475 °C embrittlement</span> Loss of plasticity in ferritic stainless steel

Duplex stainless steels are a family of alloys with a two-phase microstructure consisting of both austenitic and ferritic phases. They offer excellent mechanical properties, corrosion resistance, and toughness compared to other types of stainless steel. However, duplex stainless steel can be susceptible to a phenomenon known as 475 °C embrittlement or duplex stainless steel age hardening, which is a type of aging process that causes loss of plasticity in duplex stainless steel when it is heated in the range of 250 °C (480 °F) to 550 °C (1,020 °F). At this temperature range, spontaneous phase separation of the ferrite phase into iron-rich and chromium-rich nanophases occurs, with no change in the mechanical properties of the austenite phase. This type of embrittlement is due to precipitation hardening, which makes the material become brittle and prone to cracking.

References

  1. ↑ Jastrzebski, D. Nature and Properties of Engineering Materials (Wiley International ed.).
  2. 1 2 , Hull D., Bacon, D.J (2001); "Introduction to Dislocations", 4th ed., ISBN   0-7506-4681-0
  3. 1 2 Soboyejo, Wole O. (2003). "7.8 Crystal Structure and Dislocation Motion". Mechanical properties of engineered materials. Marcel Dekker. ISBN   0-8247-8900-8. OCLC   300921090.
  4. 1 2 3 4 Van Vliet, Krystyn J. (2006); "3.032 Mechanical Behavior of Materials" Archived 2009-09-17 at the Wayback Machine
  5. 1 2 3 4 Tong, Vivian; Wielewski, Euan; Britton, Ben (2018). "Characterisation of slip and twinning in high rate deformed zirconium with electron backscatter diffraction". arXiv: 1803.00236 .{{cite journal}}: Cite journal requires |journal= (help)
  6. ↑ Orozco-Caballero, Alberto; Li, Feng; Esqué-de los Ojos, Daniel; Atkinson, Michael D.; Quinta da Fonseca, João (2018). "On the ductility of alpha titanium: The effect of temperature and deformation mode". Acta Materialia. 149: 1–10. Bibcode:2018AcMat.149....1O. doi:10.1016/j.actamat.2018.02.022. ISSN   1359-6454.
  7. ↑ Callister, William D., Jr. (2007); "Materials Science and Engineering: An Introduction", ISBN   0-471-73696-1
  8. 1 2 Koko, Abdalrhaman; Elmukashfi, Elsiddig; Becker, Thorsten H.; Karamched, Phani S.; Wilkinson, Angus J.; Marrow, T. James (2022-10-15). "In situ characterisation of the strain fields of intragranular slip bands in ferrite by high-resolution electron backscatter diffraction". Acta Materialia. 239: 118284. Bibcode:2022AcMat.23918284K. doi: 10.1016/j.actamat.2022.118284 . ISSN   1359-6454. S2CID   251783802.
  9. ↑ Smallman, R. E.; Ngan, A. H. W. (2014-01-01), Smallman, R. E.; Ngan, A. H. W. (eds.), "Chapter 9 - Plastic Deformation and Dislocation Behaviour", Modern Physical Metallurgy (Eighth Edition), Oxford: Butterworth-Heinemann, pp. 357–414, doi:10.1016/b978-0-08-098204-5.00009-2, ISBN   978-0-08-098204-5 , retrieved 2022-10-04
  10. ↑ Sangid, Michael D. (2013-12-01). "The physics of fatigue crack initiation". International Journal of Fatigue. Fatigue and Microstructure: A special issue on recent advances. 57: 58–72. doi:10.1016/j.ijfatigue.2012.10.009. ISSN   0142-1123.
  11. ↑ Lukáš, P.; Klesnil, M.; Krejčí, J. (1968). "Dislocations and Persistent Slip Bands in Copper Single Crystals Fatigued at Low Stress Amplitude". Physica Status Solidi B (in German). 27 (2): 545–558. Bibcode:1968PSSBR..27..545L. doi:10.1002/pssb.19680270212. S2CID   96586802.
  12. ↑ Schiller, C.; Walgraef, D. (1988-03-01). "Numerical simulation of persistent slip band formation". Acta Metallurgica. 36 (3): 563–574. doi:10.1016/0001-6160(88)90089-2. ISSN   0001-6160.
  13. ↑ Akhtar, A; Teghtsoonian, A (July 1971). "Plastic deformation of zirconium single crystals". Acta Metallurgica. 19 (7): 655–663. doi:10.1016/0001-6160(71)90019-8.
  14. ↑ Gong, Jicheng; Benjamin Britton, T.; Cuddihy, Mitchell A.; Dunne, Fionn P.E.; Wilkinson, Angus J. (September 2015). "〈a〉 Prismatic, 〈a〉 basal, and 〈c+a〉 slip strengths of commercially pure Zr by micro-cantilever tests". Acta Materialia. 96: 249–257. Bibcode:2015AcMat..96..249G. doi:10.1016/j.actamat.2015.06.020. hdl: 10044/1/31552 .
  15. ↑ Wang, Leyun; Barabash, Rozaliya; Bieler, Thomas; Liu, Wenjun; Eisenlohr, Philip (August 2013). "Study of $$ \{ 11\bar{2} 1\} $$ Twinning in α-Ti by EBSD and Laue Microdiffraction". Metallurgical and Materials Transactions A. 44 (8): 3664–3674. doi: 10.1007/s11661-013-1714-y . ISSN   1073-5623. S2CID   199405954.
  16. ↑ Long, F.; Balogh, L.; Daymond, M. R. (2017-11-02). "Evolution of dislocation density in a hot rolled Zr–2.5Nb alloy with plastic deformation studied by neutron diffraction and transmission electron microscopy". Philosophical Magazine. 97 (31): 2888–2914. Bibcode:2017PMag...97.2888L. doi:10.1080/14786435.2017.1356940. ISSN   1478-6435. S2CID   136620892.
  17. ↑ Caillard, Daniel; Rautenberg, Martin; Feaugas, Xavier (April 2015). "Dislocation mechanisms in a zirconium alloy in the high-temperature regime: An in situ TEM investigation". Acta Materialia. 87: 283–292. doi:10.1016/j.actamat.2015.01.016.
  18. ↑ McCabe, R. J.; Cerreta, E. K.; Misra, A.; Kaschner, G. C.; Tomé, C. N. (2006-08-11). "Effects of texture, temperature and strain on the deformation modes of zirconium". Philosophical Magazine. 86 (23): 3595–3611. Bibcode:2006PMag...86.3595M. doi:10.1080/14786430600684500. ISSN   1478-6435. S2CID   137662799.
  19. ↑ Jiang, Jun; Britton, T. Ben; Wilkinson, Angus J. (June 2015). "The orientation and strain dependence of dislocation structure evolution in monotonically deformed polycrystalline copper". International Journal of Plasticity. 69: 102–117. doi:10.1016/j.ijplas.2015.02.005. hdl: 10044/1/25966 .
  20. ↑ Jiang, Jun; Zhang, Tiantian; Dunne, Fionn P. E.; Britton, T. Ben (January 2016). "Deformation compatibility in a single crystalline Ni superalloy". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. 472 (2185): 20150690. Bibcode:2016RSPSA.47250690J. doi:10.1098/rspa.2015.0690. ISSN   1364-5021. PMC   4786046 . PMID   26997901.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.