Department Microstructure and Residual Stress Analysis
Since monochromator upgrade in 2007 , the E3 has become faster and more adaptable to different types of measurement and has increased substantially the scientific output. Reliable near surface measurements have been made possible .
The investigations were performed on a plate with dimensions 50 x 25 x 9 mm³ made of ferritic steel 1.7255. It can be shown that the application of different methods for residual stress analysis comprising diffraction with X-ray, synchrotron and neutron radiation as well as mechanical testing allows for a complemental assessment of the residual stress state in the surface near zone and the intermediate region between the surface and the volume of mechanically surface treated material. (Fig. 1)
A custom developed (in-situ) multi-axial load frame is available to perform tensile, compressive and torsion material testing. Here, results from a steel sample measured on E3 are compared to results obtained by Bragg edge transmission imaging performed on the HZB instrument CONRAD . (Fig. 2)
In situ strain measurements during thermal cycling have been performed . Thermal load was applied with a well contacted heating wire. Temperature cycles were controlled by a thermocouple mounted on the sample in the gauge volume and connected with a computer programmed proportional – integral – derivative controller unit. (Fig. 3)
Eulerian cradles are available to study crystallographic preferred orientations, i.e. texture. For example, a polycrystalline Ni-Mn-Ga foam was studied in detail showing that the foam contains at least six randomly oriented millimeter-size grains with both 10M and 14M symmetry determined by neutron diffraction . (Fig. 4)
Furthermore, neutron diffraction experiments were performed on Ni-Mn-Ga-Co single crystalline samples at room temperature (martensitic structures) and at temperature (austenitic phase) using a cryofurnace . The picture on the right shows the hk0 neutron diffraction pattern resulting from a temperature of 500K. (Fig. 5)
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