Editing Dislocation (section)

{{Short description|Linear crystallographic defect or irregularity}}
{{About||the syntactic operation|Dislocation (syntax)|the medical term|Joint dislocation}}
[[File:Burgers Vector and dislocations (screw and edge type).svg|thumb|upright=1.5|Dislocations of edge (left) and screw (right) type.]]
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 (materials science)|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.<ref name="hull01">{{Cite book |last=Hull |first=D. |title=Introduction to dislocations |last2=Bacon |first2=D. J. |publisher=Butterworth-Heinemann |year=2001 |isbn=978-0-7506-4681-9 |edition=4th |doi=10.1016/B978-0-7506-4681-9.X5000-7}}</ref><ref>{{Cite book |last=Anderson |first=Peter M. |title=Theory of Dislocations |last2=Hirth |first2=John Price |last3=Lothe |first3=Jens |publisher=Cambridge University Press |year=2017 |isbn=978-0-521-86436-7 |edition=Third |location=New York, NY |oclc=950750996}}</ref> A dislocation can be characterised by the distance and direction of movement it causes to atoms which is defined by the [[Burgers vector]]. [[Plasticity (physics)|Plastic deformation]] of a material occurs by the creation and movement of many dislocations. The number and arrangement of dislocations influences many of the [[List of materials properties|properties of materials]].

The two primary types of dislocations are ''sessile'' dislocations which are immobile and ''glissile'' dislocations which are mobile.<ref name="radwan">{{Cite web |date=2014-05-24 |title=Dislocations in FCC materials |url=https://www.slideshare.net/omaratefradwan/mse501-ch5-radwan |access-date=2019-11-08}}</ref> Examples of sessile dislocations are the ''stair-rod'' dislocation and the [[Lomer–Cottrell junction]]. The two main types of mobile dislocations are ''edge'' and ''screw '' dislocations.

Edge dislocations can be visualized as being caused by the termination of a plane of [[atom]]s in the middle of a [[crystal]]. In such a case, the surrounding [[plane (mathematics)|planes]] are not straight, but instead bend around the edge of the terminating plane so that the crystal structure is perfectly ordered on either side. This phenomenon is analogous to half of a piece of paper inserted into a stack of paper, where the defect in the stack is noticeable only at the edge of the half sheet.

Screw dislocations create faults in a crystal that looks similar to that of a spiral staircase. These types of dislocations can be formed by cutting halfway through a crystal and sliding those regions on each side of the cut parallel to the cut to create spiraling atom planes. The dislocation line would be located in the central axis of the spiral.

The theory describing the elastic fields of the defects was originally developed by [[Vito Volterra]] in 1907. In 1934, [[Egon Orowan]], [[Michael Polanyi]] and [[Geoffrey Ingram Taylor|G. I. Taylor]], proposed that the low stresses observed to produce plastic deformation compared to theoretical predictions at the time could be explained in terms of the theory of dislocations.