Would a material with a BCC FCC or HCP lattice structure be

Would a material with a BCC, FCC, or HCP lattice structure be more prone to interstitial defects? Explain your answer.

Solution

In FCC iron, carbon atoms are located at the octahedral sites at the center of each edge of the unit cell (1/2, 0, 0) and at the center of the unit cell (1/2, 1/2, 1/2). In BCC iron, carbon atoms enter tetrahedral sites, such as 1/4, 1/2, 0. The lattice parameter is 0.3571 nm for FCC iron and 0.2866 nm for BCC iron. the HCP stucture will have the same parameters as FCC. Assume that carbon atoms have a radius of 0.071 nm.

The interstitial site in the BCC iron is smaller than the interstitial site in the FCC iron. Although both are smaller than the carbon atom, carbon distorts the BCC crystal structure more than the FCC crystal. As a result, fewer carbon atoms are expected to enter interstitial positions in BCC iron than in FCC iron.

Therefore, a material with BCC lattice structure will be more prone to interstitial defects.