Investigation of Ordering in the GOLD(11)-MANGANESE(4) Alloy System by Means of High Resolution Electron Microscopy and Diffraction.
In the framework of a research program of the Au-Mn alloy system, special attention was paid to the Au(,11)Mn(,4) alloy. It was discovered in 1964 as an unknown stable phase and therefore named "X-phase". About 10 years later, the structure has been determined to be very complex with 810 atoms in the unit cell. The relation between this structure and the phases from which it originates remained hitherto unknown and constitutes one of the objectives of the present research work. By applying high resolution electron microscopy and electron diffraction to the simpler structure of Au(,5)Mn(,2), an image code could be developed by comparison with computed images; it has been used successfully in the investigation of the Au(,11)Mn(,4) alloy. After annealing for different time periods, the alloys have been prepared for electron microscopic investigation by electropolishing with specially developed techniques. Different intermediate structures--some of which hitherto unreported--were found, most of which belonging to the cubic system. They crystallographic aspects of their formation could be deduced from the analysis of image and diffraction data. The structures of the disordered phase, the DO(,22), the AABB structure and three intermediate phases, respectively named orthorhombic, monoclinic I and monoclinic II, could be characterized. Finally, a model for the transition of the monoclinic II into the X-phase structure has been proposed. It is based on a double mechanism: the occurrence of periodic antiphase boundaries combined with a shear process on close -packed planes.
- Pub Date:
- March 1982
- Physics: Condensed Matter