Decreasing the grain dimensions of a polycrystalline substance will most likely cause a deterioration in__________________?
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Answer: B. Toughness
Explanation
Decreasing grain size increases dislocation barriers, which raises yield and tensile strength. However, restricted dislocation movement and higher strength often reduce plastic deformation capacity. Consequently, fine-grained polycrystalline materials frequently exhibit lower impact toughness and ductility. Grain boundaries impede dislocation movement through metal crystal lattices during plastic deformation. The Hall-Petch relationship mathematically links smaller grain dimensions to increased material hardness. Heat treatments like normalizing and quenching are used to refine grain structures in structural steels.
Engineers must balance strength and toughness when selecting steel grades for structural applications. While high tensile strength prevents yielding, sufficient toughness prevents sudden catastrophic brittle fracture. Aerospace components require careful microstructural control to avoid premature fatigue and impact failure. Option A is incorrect because fine grain structures often improve creep resistance at high temperatures. Option B is correct because decreasing grain size deteriorates impact toughness and ductility. Option C is incorrect because tensile strength increases rather than deteriorates with smaller grains.
- Subject
- Engineering
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- Chemical Engineering
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- medium
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