5.1 Rank the magnitudes of the diffusion coefficients from greatest to least for the following systems:
N in Fe at 700C, Cr in Fe at 700C, N in Fe at 900C, Cr in Fe at 900C
Now justify this ranking. (Note: Both Fe and Cr have the BCC crystal structure, and the atomic radii for Fe, Cr, and N are 0.124, 0.125, and 0.065 nm, respectively.
Answer:The diffusion coefficient magnitude ranking is as follows:
N in Fe at 900C;N in Fe at 700C; Cr in Fe at 900C; Cr in Fe at 700C
Nitrogen is an interstitial impurity in Fe whereas Cr is a substitutional impurity. Since interstitial diffusion occurs more rapidly than substitutional impurity diffusion. Also the magnitude of the diffusion coefficient increases with increasing temperature.
5.2 Consider the self-diffusion of two hypothetical metals A and B. On a schematic graph of ln D versus 1/T, plot (and label) lines for both metals given that D0(A) >D0(B) and also that Qd(A) > Qd(B).
6.1 Cite the primary differences between elastic, anelastic, and plastic deformation behaviors.
Answer: Elastic deformation is time-independent and nonpermanent, anelastic deformation is time-dependent and nonpermanent, while plastic deformation is permanent.
6.2 Of those metals listed in Table 6.3(see book),
(a) Which will experience the greatest percent reduction in area? Why?
(b) Which is the strongest? Why?
(c) Which is the stiffest? Why?
(a) Material B will experience the greatest percent area reduction since it has the highest strain at fracture, and, therefore is most ductile.
(b) Material D is the strongest because it has the highest yield and tensile strengths.
(c) Material E is the stiffest because it has the highest elastic modulus.