A TEM study on the semicoherent precipitates in a Nb-19%Mo alloy

We have investigated the structure of planar carbide particles of several hundred nm in diameter and 10-50 nm in thickness, formed in a Nb-19%Mo alloy during a creep test at 1773 K. The planar particles are composed of the face-centered cubic (fcc) NbC phase. They precipitate in a partially coherent manner with habit planes close to 10 3 0 bcc or 3 1 0 bcc; while the orientation relationship (OR) is close to (1 0 0)bcc//(1 1 0)fcc, [0 0 1]bcc//[0 0 1]fcc, which is the well-known Bain OR, with a rotational mismatch of 5.7 (plus-minus) 0.2° around the [1 0 0]bcc axis. Numerous 1 1 1 fcc stacking faults exist inside the precipitates, suggesting they deformed plastically during growth. These findings are in excellent agreement with predictions provided by the invariant line theory.