Question

9. For each of the sets below, circle the option which will be STRONGER: (2 points each) Set 1: polycrystalline Au Set 2: Fe with mean grain size of 10 pm Set 3: Ni with 20 wt% Cu added Set 4: Brass cold worked 25% Set 5: Ti cold worked 25% then annealed OR OR OR OR OR single crystal Au Fe with mean grain size of 1 um Pure Ni Brass cold worked 0% Ti cold worked 25%

Answer 1

1. Polycrystalline Au is stronger than single crystalline Au because the grain size of crystals in polycrystals are much more finer than in single crystals it is difficult to break the bonds in them.

2.Fe with mean grain size of 1 micro meter is stronger because mean grain size is inversely proportional to the strength. The larger the grain size, less stress will only be required for dislocation of crystals so less will the strength.

3.Ni with 20Wt% Cu added is stronger than pure Ni because in the case of alloys it consists of different sized atoms of different metals so it makes it stronger from sliding away.

4. Brass cold worked 25% is stronger as it improves the tensile strength.

5.Ti cold worked 25% is stronger because annealing is used for reducing the hardness.