Experimental reinvestigation of Al-Co phase diagram in vicinity of Al13Co4 family of phases

The work is focused on the experimental reinvestigation of the Al-Co phase diagram in vicinity of the Al13Co4 family of phases. For this purpose several alloys were prepared with bulk compositions ranging between Al71Co29 and Al77Co23. Experimental samples processed of the as-cast alloys were annealed for 330 h at various temperatures between 1070 and 1150 degrees C and subsequently rapidly cooled to fix their high-temperature microstructures. The annealing temperatures were selected with respect to the earlier published Al-Co phase diagrams. In the investigation X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy including both energy dispersive X-ray spectroscopy and electron backscatter diffraction were used. In the microstructures of as-annealed alloys various combinations of B-2-AlCo, Al5Co2, Z-Al3Co, Y-1-Al13Co4, Y-2-Al13Co4, M-Al13Co4, O'-Al13Co4, and solidified liquid were identified. It was found out that the earlier published single-phase Y-area is comprised in fact of monoclinic Y-1-Al13Co4 and orthorhombic Y-2-Al13Co4 lamellas. From the thermodynamic point of view, Y-1-Al13Co4 and Y-2-Al13Co4 are stable and metastable phases, respectively. The O'-Al13Co4 phase was identified at 1070 degrees C in the alloys where the occurrence of O-Al13Co4 was expected. A modified partial Al-Co phase diagram was also proposed with respect to the experimental results obtained. (C) 2015 Elsevier B.V. All rights reserved.