Materials Science TEST on 97-1-22:



 
Answer all two questions.
 
(1) Diffusion in solids
  Explain in one sentence why diffusion can take place in a solid, that consists of a lattice packed with atoms?

The composition of a material that has different concentrations of impurities in different parts of it will change with time, because of diffusion. The composition of a pure substance does not change in time. Does diffusion occur in such pure solid?

"Diffusivity" is defined by Fick's first law. Write down this law, define all its symbols, and deduce the S.I units for diffusivity.

 

(2) Critical resolved shear stress
  A stress of 1 MPa is applied along the [111] direction of a single crystal of FCC metal. What is then the critical resolved shear stress along the [111] direction within its (101) plane?
 

END


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