Steel is produced when small carbon atoms occupy interstitial sites within the body-centered cubic (bcc) lattice of iron. In contrast, bronze is formed when tin atoms substitute for copper atoms in a face-centered cubic (fcc) lattice.
For each alloy, construct and analyze a representative particle-level model.
a. Part 1: (a) Draw a two-dimensional slice through one bcc unit cell of pure iron viewed along a body diagonal. Then add carbon atoms to depict an alloy that is 6.7% C by atom (the composition of cementite, Fe3C). Indicate clearly which sites are interstitial.
b. Part 2: (b) Draw a separate two-dimensional slice through one fcc unit cell of pure copper. Modify the diagram to show a substitutional alloy that is 12.5% Sn by atom (representative of Cu7Sn). Identify the sites where Sn is located.
c. Part 3: (c) For each alloy, determine the coordination number of the solute atom (C in steel, Sn in bronze) with respect to its immediate metallic neighbors, based on your diagrams.
d. Part 4: (d) Using the coordination numbers and geometric differences you identified, compare and contrast how interstitial and substitutional alloying affect hardness and electrical conductivity.