Why does a decrease in dislocation density result in decrease in yield strength and increase in ductility?A slightly detailed explanation is what I am looking forward to.

  • $\begingroup$ @SolarMike What do you want me to include there? $\endgroup$ Commented Mar 22, 2021 at 12:04
  • $\begingroup$ @SolarMike Sorry. $\endgroup$ Commented Mar 22, 2021 at 12:05
  • $\begingroup$ What materials are of interest? I suspect dislocations in a quartz crystal affect ductility rather less than the same in semicrystalline samples of metal. $\endgroup$ Commented Mar 22, 2021 at 14:12
  • $\begingroup$ mild steel @CarlWitthoft $\endgroup$ Commented Mar 22, 2021 at 15:15

1 Answer 1


Dislocations travel through a metal crystal while it is being deformed; it is in fact dislocation movement which makes metal crystals yield and deform at loads far below that which you could calculate on the basis of interatomic forces in a perfect lattice.

These mobile dislocations tend to pile up against one another and become entangled as the material deforms; these pileups inhibit further deformation and the material becomes more resistant to deformation than it was originally. This furnishes the basis for cold work as a strengthening mechanism.

If there are not many dislocations in the crystal to start with, then those which are present find it easy to move, and it is easy to form new ones from things like stacking faults within the crystal. This makes the crystal ductile- at least until dislocation pileup sets in.

  • $\begingroup$ Ok but what has this to do with internal stress. $\endgroup$ Commented Mar 23, 2021 at 2:30
  • $\begingroup$ Internal stress (that is, strain energy stored in the crystals) is associated with dislocation pileups. $\endgroup$ Commented Mar 23, 2021 at 3:25

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