Carbon diffuses in iron via an interstitial

 mechanism—for FCC iron from one octahedral

site to an adjacent one. In Section 4.3 (Figure

4.3a), we note that two general sets of point coor￾dinates for this site are 0 1

2 1 and 1

2

1

2

1

2. Specify the

family of crystallographic directions in which this

diffusion of carbon in FCC iron takes place.