Example interstitial sites for carbon in iron in fcc

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Example: Interstitial Sites for Carbon in Iron In FCC iron ( a 0 =0.3571nm ), carbon atoms are located at octahedral sites (CN=6) at: -the Center of each edge of the unit cell (1/2, 0, 0), and -the Center of the unit cell (1/2, 1/2, 1/2). atoms C atoms Fe
11 Example: Interstitial Sites for Carbon in Iron In BCC iron ( a 0 =0.2866nm ), carbon atoms enter tetrahedral sites (CN=4), such as (1/4, 1/2, 0).
12 Substitutional Atoms Larger substitutional atoms Smaller substitutional atoms Both distort the lattice and strain the bonds over a large surrounding volume.
13 Solid Solutions: a. Substitutional Solid Solutions e.g.: Cu-Ni alloy Good solubility occurs between two metals if they have: -a difference less than about 15% in atomic radii; -the same crystal structure; -similar electronegativities; -the same valence.
14 Solid Solutions: a. Interstitial Solid Solutions e.g.: Steel (Fe-C alloys) Because r C << r Fe and the strain field created around the Fe –C couple, solubility of C in a-Fe is < 0.1%, i.e. they have partial or limited solid solubility.

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