Microstructural characterization by indirect inspection methods
Project manager: Gerald Zickler
Indirect experimental methods such as small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) with high-energy synchrotron radiation are used in the Christian Doppler Laboratory “Early Stages of Precipitation” for the characterization of nanometer-sized precipitates in large sample volumes. These methods are powerful experimental techniques for obtaining quantitative and statistically relevant data for the characterization of size, shape, arrangement, and volume fraction of precipitates. The interpretation of scattering patterns usually requires additional microstructural information from complementary methods, e.g. transmission electron microscopy (TEM) or three-dimensional atom probe tomography (APT). Only a combination of these methods provides a comprehensive microstructural understanding of a material.
Scattering techniques offer the advantages of investigating materials in-situ at high temperatures using special furnaces and heating cells, or under external load at tensile testing. With in-situ experiments, the entire path of phase transformations can be seen on one single specimen, avoiding possible influences from local differences in microstructure and chemical composition. Furthermore, in-situ studies allow the detection of rather early stages of precipitation.
Recently in-situ SANS experiments of a nickel-based superalloy were performed at the Institut Max von Laue – Paul Langevin (ILL) in Grenoble , France . Figure 1 shows azimuthally averaged SANS patterns of the nickel-based superalloy in-situ aged at two different temperatures for various aging times (see legend). A considerable increase in scattering intensity is observed after aging, resulting from the formation of intermetallic phases during the heat treatment .
XRD using high-energy synchrotron radiation was applied for in-situ studying of the reverse martensitic phase transformation under external load in a maraging steel. These experiments were performed at the GKSS Engineering Materials Science Beamline HARWI-II at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg , Germany . Figure 2 shows a typical series of XRD patterns during tensile testing, where the phase transformation as function of strain e can be seen as change of the scattering intensities for the individual diffraction peaks .
Figure 1 Azimuthally averaged in-situ SANS patterns of a nickel-based superalloy aged at 1048
and 1148 K for various aging times (see figure legend).
Figure 2: A series of in-situ XRD patterns using high-energy synchrotron
radiation during tensile testing of a maraging steel.
 G.A. Zickler, R. Schnitzer, R. Radis, R. Hochfellner, R. Schweins, M. Stockinger, H. Leitner: Mater. Sci. Eng. A (2009) in press.
 G.A. Zickler, R. Schnitzer, R. Hochfellner, T. Lippmann, S. Zinner, H. Leitner: Int. J. Mater. Res. (formerly Z. Metallkd.) (2009) in press.