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When we look at images of edge or screw dislocation, it seems as if the direction in which that dislocation will move is already fixed by the 'way the dislocation is present'. For example, take any image of edge dislocation, and say the top half is moving with respect to the bottom.

enter image description here

However:

Dislocations will move in the direction of slip direction and on the slip plane. That is the dislocation motion direction is dictated by the slip system of that crystal (FCC, BCC or HCP)

Hence, only in the case when the plane between the top and bottom is also a slip plane, things work out. But what happens when the plane between the top and the bottom set of atoms is not a slip plane for that particular crystal?

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  • $\begingroup$ x-posted on engineering: engineering.stackexchange.com/q/15177 $\endgroup$ – AccidentalFourierTransform May 25 '18 at 19:01
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    $\begingroup$ I think that in order for a dislocation to be formed in the first place by a mechanism such as a Frank-Read source, the plane in question has to be a slip plane. However, if a dislocation somehow is created on a non-slip plane by some other mechanism, it still may be possible for it to move by dislocation climb, although that is a slower, diffusion controlled process. $\endgroup$ – Samuel Weir May 25 '18 at 19:07
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    $\begingroup$ @SamuelWeir - of splitting into mobile partials on slip planes (although usually splitting into partials results in one not being mobile). $\endgroup$ – Jon Custer May 25 '18 at 19:30
  • $\begingroup$ @JonCuster Can you help me in thermodynamics?What is chemical potential $\endgroup$ – gateprep Aug 17 '18 at 20:32
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There are cases, when two mobile dislocations (dislocations with Burgers vector pointing into a slip plane, therefore, can move with gliding) contact-interact and form a third dislocation. If this two dislocations split up into two-two Shockley partial dislocations, and one Shockley partial dislocation contact-interact with the other dislocation's Shockley partial dislocation, they can form a dislocation with Burger's vector not matching any slip plane. This dislocation cannot glide, therefore, became immobile, i.e. fixed. This is called a Lomer–Cottrell junction.

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