Difference between Hardness and Toughness

Hardness i. It is the property of the material to resist scratching, abrasion, indentation or penetration. ii. Hardness of a material is stated relative to the hardness of other material.   iii. Important in shafts, bearing whichever is having relative motion.

Toughness i. Ability of a material to withstand both elastic and plastic deformation, shock and vibration. ii. Toughness is measured in terms of the energy a material can absorb before a actual failure takes place. iii. Important in structural members, machine parts which are subjected to shock and vibration. E.g. shafts, spring.