Ashley Bucsek, BeamTeam PhD candidate, performed the first-ever dark-field X-ray diffraction measurements on shape memory alloys at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The video clips below show that she was able to capture subgrain microstructure features, including dislocations nucleating from carbide interfaces.
The “Rocking at high temp” video above shows the sample being rocked at high temperature, revealing the initial austenite microstructure. Intensity corresponds to austenite volume, and the angle at which it lights up corresponds to strain.
As the sample is rocked at low temperature, the martensite structure shows, especially toward the top. Intensity corresponds to austenite volume, and the angle at which it lights up corresponds to strain.
While the sample cooled (without rotating), snapshots were taken every couple of degrees. It starts out austenite (bright areas indicate high volume), and then the austenite goes away as the martensite comes in.
Ashley is working as a visiting scientist at the ID06 beamline at ESRF, funded by an NSF GROW award. The dark-field X-ray microscopy (DFXM) technique is a high-resolution X-ray diffraction microscopy technique pioneered by the scientists at ESRF. This technique offers the capability to measure both dislocation density and elastic lattice strains with a spatial resolution of 70–100 nm; orientation and strain can be mapped with a sensitivity of 0.1 mrad and 10-4, respectively—superior performance to that of transmission electron microscopy (TEM). Ashley is using DFXM to study interfacial strain fields in phase transformation in connection to hysteresis and functional fatigue.