Pseudoelasticity Micromechanism Of Fe₃Al Single Crystal Study By Synchrotron High-Energy X-Ray Diffraction

Iron aluminides based on Fe3Al have attractive properties for structural applications at intermediate temperatures, including good oxidation resistance and low density. As a kind of shape memory alloy, it also have some particular properties, such as shape memory effect and pseudoelastisity, which have been receiving increasing attention in recent years and are extensively used in many fields, such as industry, aviation, national defense, instruments and medical devices, etc.Pseudoelastic behaviour of DO3-ordered Fe3Al single crystals was investigated by the in-situ high-energy X-ray diffraction technique based on the synchrotron source in this paper. When large pseudoelasticity took place in the crystals, a superpartial dislocation with Burger's vector (b) of 1/4<111> moved individually dragging the nearestneighbour antiphase boundary (NNAPB) during loading. During unloading,1/4<111>superpartials moved back due to the surface tension of the NNAPB, which caused the pseudoelasticity. It was found that the pseudoelastic behaviour associated with this deformation modes was strongly affected by stress sense and loading axis.During in-suit experiment of DO3-ordered Fe3Al single crystals under compression process, low-index diffraction spots were collected by a Mar3450 on-line image-plate scanner. By line analysis from diffraction spots with Fit-2D. GSAS software, it is possible to acquire in-situ information of the lattice strain and microstrain for compression samples. And three-dimensional X-ray diffraction scattering pattern can be provided by Matlab software. The results will show the evolution of microstress under the macrostress, and the 2D,3D diffraction patterns as applied stress at different loading cycles.The main conclusions in this dissertation are as follows:1. Strain recovery decreases as increasing maximal strain and pseudoelastic behaviour disappears gradually as increasing applied stress for DO3-ordered monocrystalline Fe3Al.2. Serration are produced on the lattice strain-stress curves, which are accompainied by the broadening and opposite displacement of diffraction peaks, illuminate the appearance of stacking fault during compressing process.3. The mutual effect of antiphase takes important part in pseudoelastic behaviour. The microstrain curves decrease acutely during pseudoelastic compression, show the appearance of microstructure transformation during this process.4. When loading with compression axes along<419> orientations, the intense diffuse rods of (110) plane diffraction spots scatter along [111] orientation.5. The diffuse intensities increase, when increase applied stress and compression ratio, and the shape of superlattice diffraction spots are no long recovery to initial statement, as the unreversible microstructure transformation happens.