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GATE 2019 MT – Question 27

Mechanical Behaviour of Materials · Creep · 1 mark · Multiple choice

In a tensile creep test, Nabarro–Herring creep is favoured over Coble creep by

  1. Larger grain size and lower temperature
  2. Smaller grain size and higher temperature
  3. Larger grain size and higher temperature
  4. Smaller grain size and lower temperature

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Correct answer: (C) Larger grain size and higher temperature

Explanation

Nabarro–Herring creep uses lattice diffusion and scales roughly as d⁻²; Coble creep uses grain-boundary diffusion and scales as d⁻³. Increasing grain size suppresses Coble creep more strongly. Higher temperature favours lattice diffusion relative to the boundary route. Thus C.

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