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Technical University of Munich
Technical University of Munich

Growth of precipitates and changes in their morphologies

Dr. Ralph Gilles

To observe precipitates in multiphase alloys (e.g. superalloys) different probes can be used. Microscopy and scattering methods are complementary tools for such investigations. Especially in scattering techniques using neutrons, diffraction and small-angle scattering provide information (from bulk samples) on the structure, morphology, size distribution and volume fraction of any inhomogeneities, e.g. precipitates embedded in a matrix. As an example of the unique possibilities in neutron research in-situ measurements at high temperature (up to melting point of the superalloys) could be done taking advantage of the large dimensions of a neutron beam and the easy handling of sample environment.

Fig. 1 shows a typical image of a multiphase superalloy which contain nano-sized co-precipitates of γ’ + γ’’. Changes of precipitate morphology caused by exposure at different temperatures were studied and some results are shown in Fig. 2.

Figure 1: Bright field TEM image of non-compact type co-precipitates of γ' / γ'' in Inconel 706, a Ni-base superalloy. Inset shows a magnified image depicting the morphology of 8 – 10 nm size sandwiched co-precipitates, where the bright core is Ni3Al-type γ’ phase and the dark lobes are Ni3Nb-type γ’’ phase.
Figure 2: Fig. 2: One dimensional SANS patterns of measured Inconel 706 samples given different heat treatments. Differential cross section dσ/dΩ versus scattering vector Q (measured at V4 instrument at HMI, Berlin).