Question

• Why do metals initially exhibit only elastic deformation under low loads?

• What causes metal plastic deformation to begin at higher stress levels?

• What occurs in metals on the atomic level that causes plastic deformation at high stress?

• What occurs in molten metals when they cool and solidify, both initially and then later?

Answer 1

1.Elastic deformation means the deformation which is recoverable after removal of load and it returns to original position due to return of atom to its original position.And generally materials have high yield strength than other materials and yield strength means the load after which if we remove the load the atoms can not return to its original position and elastic deformation will not occur.So for low loads the metal lies on the elastic zone and they could not be permanently deformed so they only exhibit elastic deformation.

Answer for Q2 & Q3 -.At higher stress(beyond yield strength) the carbon atoms slipping occurs in the molecular structure of metal so plastic deformation starts and after the removal of load the deformation is not recoverable.

4.solidification means the transformation from liquid to solid and it occurs below the melting point.Solidification will take place when the temperature is lower than the melting point of the metals.The solidification of metal occur by nucleation and growth transformation.The first step of metal solidification is creation of tiny,stable nuclei in the liquid metal. Cooling the liquid below its equilibrium freezing temperature, or under-cooling,provides the driving force for solidification.Once a cluster reaches a critical size, it becomes a stable nucleus and continues to grow.so initially the stable nuclei is formed due to nucleation and later the growth occurs where growth is the physical process by which a new phase increases in size. In the case of solidification, this refers to the formation of a stable solid particle as the liquid freezes.