The GATE Grind

GATE 2024 MT – Question 48

Mechanical Behaviour of Materials · Creep · 2 marks · Multiple select

A creep test of a pure polycrystalline metal is performed in tension and the creep strain rate is observed to decrease during the primary stage. The creep mechanism is later determined to be dislocation-climb-controlled. The observed decrease in creep strain rate is/are due to

  1. an increase in dislocation density.
  2. grain growth.
  3. a decrease in the dislocation density.
  4. an increase in the cross-sectional area of the sample.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) an increase in dislocation density.

Explanation

During primary creep, increasing dislocation density strengthens the material through dislocation interactions and raises resistance to further motion.

Until recovery balances hardening, this lowers the creep rate.

Therefore **A**.

The stated climb-controlled mechanism does not make grain growth or a decreasing density the primary hardening explanation.