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)//(0 0 1)(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 degrees around the [10 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. (c) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.