Phase equilibria of the Al-Fe-Ni system at 850 °C and 627 °C

The phase equilibria at 850 °C and 627 °C in the Al-Fe-Ni system with Al content above 50 at.% are investigated by using 19 alloys. The annealed alloys are examined by means of X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and electron probe microanalysis (EPMA). It is confirmed that τ2 phase (Al10Fe3Ni) with hexagonal structure and τ3 phase (Al71Fe5Ni24) with the decagonal quasi-crystalline structure, exist at 850 °C. The homogeneity of τ2 spans in the range of 5.7-13.1 at.% Ni and 14.4-22.2 at.% Fe. At 850 °C, the maximum solubilities of Ni in Al5Fe2 and Al2Fe are determined to be 1.3 at.% and 2.1 at.%, respectively, while the maximum solubility of Fe in Al3Ni2 is measured to be 4.9 at.%. At 627 °C, τ1 (Al9FeNi) and τ2 exist. At this temperature, the homogeneity range for τ1 is from 8.7 at.% to 14.3 at.% Ni and 4.5 at.% to 10.0 at.% Fe, and that for τ2 is within the range of 7.2-12.4 at.% Ni and 15.6-22.5 at.% Fe. The maximum solubilities of Ni in Al13Fe4, Al5Fe2 and Al2Fe are determined to be 8.9, 1.5, and 2 at.%, respectively, while that of Fe in Al3Ni is measured to be 3.6 at.%. At 627 °C, the maximum solubilities of both Fe and Ni in (Al) phase are determined to be extremely small, about 0.58 at.% for both elements.