Interstitial Solid Solutions

Interstitial solid solution of C in α-Fe. The C atom is small enough to fit, after introducing some strain into the BCC lattice.

Factors for high solubility:

• For fcc, bcc, hcp structures the voids (or interstices) between the host atoms are relatively small ⇒ atomic radius of solute should be significantly less than solvent Normally, max. solute concentration ≤ 10%, (2% for C-Fe).

Composition / Concentration:

Composition can be expressed in

• weight percent, useful when making the solution
• atom percent, useful when trying to understand the material at the atomic level

Weight percent (wt %): weight of a particular element relative to the total alloy weight. For two component system, concentration of element 1 in wt. % is

Atom percent (at %): number of moles (atoms) of a particular element relative to the total number of moles (atoms) in alloy. For two-component system, concentration of element 1 in at. % is

where nm1 = m’1/A1 m’1 is weight in grams of element 1, A1 is atomic weight of element 1)