Deformation twinning in 2-phase Ni-25Mo-8wt%Cr alloy samples, which contained Ni2(Mo,Cr) precipitates in a face-centered cubic matrix, was studied by means of transmission electron microscopy. It was found that the normal twinning variant in the disordered face-centered cubic matrix phase, which corresponded to the pseudo-twinning mode in the ordered body-centered orthorhombic Ni2Mo phase, altered the nearest-neighbor environment. The effect of this was to produce a new superstructure, with tetragonal symmetry, in the twinned regions of Ni2Mo precipitates. Experimental electron diffraction scans across this pseudo-twinned structure were related to the crystallography of the phases.

M.Kumar, V.K.Vasudevan: Acta Materialia, 1996, 44[9], 3575-83