  Scanning nano-beam electron diffraction with a pixelated detector was
employed to investigate the orientation relationship of nanometer sized,
irradiation induced G-phase (M$_6$Ni$_{16}$Si$_{7}$) precipitates in an
austenite matrix. Using this detector, the faint diffraction spots originating
from the small G-phase particles could be resolved simultaneously as the
intense matrix reflections. The diffraction patterns were analyzed using a
two-stage template matching scheme, whereby the matrix is indexed first and the
precipitates are indexed second after subtraction of the matrix contribution to
the diffraction patterns. The results show that G-phase forms with orientation
relationships relative to austenite that are characteristic of face-centered
cubic (FCC) to body-centered cubic (BCC) transformations. This work
demonstrates that nano-beam electron diffraction with a pixelated detector is a
promising technique to investigate orientation relationships of nano-sized
precipitates with complex crystal structures in other material systems with
relative ease.
