Explain the following observations i Why is it often easier

Explain the following observations:

(i) Why is it often easier to bend a metal bar than to straighten it out again?

(ii) Nickel can be strengthened by adding small hard particles of thoria

(iii) At room temperature, pure silver has a yield strength of about 50 MPa, but pure silicon has a yield strength of about 2.6 GPa.

Solution

(i)

It is easier to bend the metal bar because initially the metal would be soft thereby allowing the deformation to take place. But as a metal is deformed, it\'s dislocation density increases and it becomes harder to deform further. Thus, straightening out the metal bar would be difficult and will only happen if we apply a much higher force.

(ii)

Particles of thoria can strengthen nickel due to dispersion strengthening. The strength and hardness of nickel is enhanced by the presence of extremely small and uniformly dispersed thoria particles within the original phase matrix.