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GATE 2023 MT – Question 51

Mechanical Behaviour of Materials · Dislocations and strengthening · 2 marks · Multiple select

A dislocation loop PQRSTU lies on the (111) plane of a cubic single crystal, with Burgers vector $(1/6)[\bar1 2\bar1]$. Segments $\overrightarrow{PU}$ and $\overrightarrow{PQ}$ are parallel to $[0\bar1 1]$ and $[1\bar1 0]$, respectively. Choose all correct statements.

Diagram for GATE 2023 MT question 51
  1. Dislocation segment PQ is mixed in character.
  2. Dislocation segment UT is screw in character.
  3. Dislocation segment PU is mixed in character.
  4. Dislocation segment QR is edge in character.

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Show answer and explanation

Correct answer: (A) Dislocation segment PQ is mixed in character.; (B) Dislocation segment UT is screw in character.; (C) Dislocation segment PU is mixed in character.

Explanation

The Burgers direction is $[-1,2,-1]$. Its dot products with PQ direction $[1,-1,0]$ and PU direction $[0,-1,1]$ are both −3. Neither segment is perpendicular or parallel to the Burgers vector, so both are mixed. The horizontal UT and QR segments in the shown (111) plane are parallel to the Burgers vector, making both screw. Correct choices: **A, B, C**.