Question

11)Describe the three mechanisms in detail for how a material can be strengthened. Make sure to explain the mechanic and reasoning for why each strengthens the material.

Answer 1

The three mechanisms which can be used to increase the hardness and which also increases the strength of the material . The three mechanism which can be used to increase the strength of the material are mentioned below :

• Solid Solution Strengthening
• Grain Size Strengthening
• Strain Hardening

SOLID SOLUTION STRENGTHENING :

In this method we would improve the hardness which increases the strength by alloying with other impurity atoms that would settled down in the vacant spaces/voids in the solid solution . By increasing the concentration of the impurity atoms would results in increase in the tensile and yield strength . The solid solution has the higger yield strength than the pure solution . In a pure element all atoms are equi-sized , now we will substitute the middle atom with a bigger atom in the center that is called as susbstituional solute . Due to its bigger size it will cause dislocation of the other atoms so as to get fitted into that space . It forms a strain field around the solute atom .  Now we will add an interstitial solute in the void , if the size of the solute is bigger than the void then it would again displaces the neighbouring atoms . This would cause impediment in the dislocation . HIgher would be the size difference higher would be the strain .

STRENGTHENING BY GRAIN SIZE REDUCTION :

In a single crystal all the atoms are oriented in a single way , but in case of a polycrystal orientation of the unit cell changes from region to region which is termed as crytalline cell . The change in the orientation creates a grain boundaries , where distrubance occurs . The slip plan countunity is broken in case of polycrystal becuase of hrain boundaries . So the dislocation motion is distrupted by grain boundaries , their are two types of grains which is coarse and fine grains . In case of finer grains we have more grain boundaries which results in more obstruction to dislocation motion and thereby producing higher strain which means higher would be the strength .

STRAIN HARDENING :

In this we are going strength the crystalline solid , which is deforming plastically with the help of disloaction . In this initially the it deforms elastically but then it remains a straigth line in the elastic part and then the curve becomes non linear and plastic deformation begins at this stage . The sample has been deformed thats why it has become elongated in size as compared to its original state . Now the yield stress changes which causes the change in the earlier yield stress which makes the material has more strength than ther earlier one .

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