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 ± 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.