Question

Why carbon preferintially sits in octahedral voids?

Answer 1

Answer:

FCC has 8 and 4 octahedral and tertrahedral voids per unit cell respectively. whereas BCC has 12 and 6 respectively. octahedral in FCC is bigger than tertrahedral. C occupies octahedral with less distortion. Octahedral in BCC is smaller than tertrahedral. even in that case C occupies octahedral void due to lesser distortion (only top atom and bottom need to be distorted). No. of voids in BCC are more than FCC whereas size of voids in BCC are significantly smaller than FCC. For this reason austenite have higher solubility of C than ferrite.