# GATE MT 2017 Q9. Both creep resistance and tensile strength of a metal can be enhanced by the:

GATE MT 2017 Q9. Both creep resistance and tensile strength of a metal can be enhanced by the:

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Askmemetallurgy Official

Asked: 2020-06-28T16:19:06+05:30
2020-06-28T16:19:06+05:30In: Mechanical Metallurgy

14.29%A. Increase in the grain size ( 7 voters )
22.45%B. Decrease in the grain size ( 11 voters )
61.22%C. Addition of dispersoids ( 30 voters )
2.04%D. Annealing ( 1 voter )

Based On 49 Votes

GATE MT 2017 Q9. Both creep resistance and tensile strength of a metal can be enhanced by the:

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The correct option is C. We know that the tensile strength of materials can be enhanced by several strengthening mechanisms like: Solid solution strengthening Grain Boundary Strengthening Dispersion Strengthening Strain hardening and some more processes. As per question if we see there are two mechaRead more

The correct option is C.

We know that the tensile strength of materials can be enhanced by several strengthening mechanisms like:

and some more processes.

As per question if we see there are two mechanisms which can support the tensile strength enhancement which are;

1) The decrease in grain size which will provide grain boundary strengthening by increasing the grain boundaries and thus more hindrance to the dislocations motion.

2) the addition of dispersoids which will give dispersion strengthening by spreading in the solution and acting as obstacles to the dislocation motion.

to choose let’s move on to the second criteria of question which is the creep resistance.

The creep as we know is time-dependent deformation at constant loads is more active at higher temperatures. But at higher temperatures say above the equicohesive temperature( T> 0.5Tm), the grain boundary becomes weaker than the grains and their sliding occurs. So in this case the course grain provides stronger creep strength as it will decrease the grain boundaries and so less sliding. thus decreasing grain size will have negative effect on creep strength.

The dispersoids addition, however, increases the resistance to dislocation motion and also hinders the diffusion of the atoms. thus the fine carbides like dispersoids are always taken into consideration to make the microstructure complex and increase the creep strength of the material.

Thus we can see that the addition of dispersoids can play a common role and hence option C is correct.

See lessCorrect answer is option C. @Rohit.km described it best. Thank you.

Correct answer is option C. Rohit jha.km described it best. Thank you.

See lessAddition of dispersoids will help in achieving both- high tensile strength and high creep strength. However, strength can be increased by grain refinement also, but to enhance creep strength coarse grains are preferred. Therefore, dispersoids serve us both purposes the same time.

Addition of dispersoids will help in achieving both- high tensile strength and high creep strength. However, strength can be increased by grain refinement also, but to enhance creep strength coarse grains are preferred. Therefore, dispersoids serve us both purposes the same time.

See less