GATE 2025 MT – Question 60
Nabarro–Herring diffusion creep controls deformation in polycrystalline Ni at a certain temperature. The steady strain rate is $10^{-8}\ \mathrm{s^{-1}}$ at 10 MPa. The stress giving $10^{-9}\ \mathrm{s^{-1}}$ at that temperature is ______ MPa (in integer). Assume the same mechanism remains rate controlling.
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Correct answer: 1 to 1
Explanation
At fixed temperature and grain size, Nabarro–Herring creep is linear in stress: $\dot\epsilon=C\sigma$.
The rate decreases by a factor of ten, so the stress does too: $\sigma_2=10(10^{-9}/10^{-8})=\boxed{1\ \mathrm{MPa}}$.