CONVERGENT-BEAM DARK-FIELD IMAGING TECHNIQUE WITH ITS APPLICATION TO OBSERVATION OF MULTIPHASE MATERIALS

A new technique for the observation of multiphase materials has been p roposed, which enables us to distinguish easily different phases by th eir different contrasts. The technique is based on the broadening of d iffraction spots and the overlapping of dark field images due to beam convergence. Since contrasts are adjustable by changing the beam conve rgence, the contrast of a weak diffraction phase can be made brighter than a strong diffraction phase. An observation of the precipitates in a Ti-10V-2Fe-3Al alloy by this technique showed that a stable oc phas e precipitates nucleating at the metastable omega phase in the supersa turated beta matrix.