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

Abstract The work is focused on the experimental reinvestigation of the Al–Co phase diagram in vicinity of the Al 13 Co 4 family of phases. For this purpose several alloys were prepared with bulk compositions ranging between Al 71 Co 29 and Al 77 Co 23 . Experimental samples processed of the as-cast alloys were annealed for 330 h at various temperatures between 1070 and 1150 °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 B2-AlCo, Al 5 Co 2 , Z-Al 3 Co, Y 1 -Al 13 Co 4 , Y 2 -Al 13 Co 4 , M-Al 13 Co 4 , O′-Al 13 Co 4 , 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 -Al 13 Co 4 and orthorhombic Y 2 -Al 13 Co 4 lamellas. From the thermodynamic point of view, Y 1 -Al 13 Co 4 and Y 2 -Al 13 Co 4 are stable and metastable phases, respectively. The O′-Al 13 Co 4 phase was identified at 1070 °C in the alloys where the occurrence of O-Al 13 Co 4 was expected. A modified partial Al–Co phase diagram was also proposed with respect to the experimental results obtained.