a) Define creep and specify the conditions under which it occurs? b) Discuss three metallurgical/Processing techniques that are employed to enhance the creep resistance of metal alloys.

  a) Define creep and specify the conditions under which it occurs?       

         Creep is the tendency of a solid material to deform permanently under the influence of persistent mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material.

b) Discuss three metallurgical/Processing techniques that are employed to enhance the creep resistance of metal alloys. 

          Generally, materials have better creep resistance if they have higher melting temperatures, lower diffusivity, and higher shear strength. Close-packed structures are usually more creep resistant as they tend to have lower diffusivity than non-close-packed structures. Common methods to reduce creep include:

Solid solution strengthening: adding other elements in solid solution can slow diffusion, as well as slow dislocation motion via the mechanism of solute drag.

Particle dispersion strengthening: adding particles, often incoherent oxide or carbide particles, block dislocation motion.

Precipitation hardening: precipitating a second phase out of the primary lattice blocks dislocation motion.

Ref: Wikipedia