Fe-Ni-Si (Iron-Nickel-Silicon)

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Phase Diagram Evaluations: Section II

Fe-Ni-Si (Iron-Nickel-Silicon) V. Raghavan

The ﬁrst review of this system by [1988Ray] presented a tentative liquidus projection, partial isothermal sections at 1000, 800, 600, and 450 C for Ni-rich alloys, two computed isothermal sections at 1127 and 727 C, and a reaction scheme. Two updates gave an additional computed isothermal section at 427 C [1994Rag] and partial sections in the order-disorder region of Fe-rich alloys at 1200, 1100, 1000, 800, and 650 C [2003Rag]. Recently, [2004Him] and [2005Him] reinvestigated the Ni-rich region with special reference to the fcc (c)/L12 (c¢) equilibria.

Binary Systems In the Fe-Ni phase diagram, a continuous face-centered cubic solid solution (denoted c) forms between cFe and Ni and is stable over a wide range of temperature. At 517 C, an ordered phase FeNi3 (L12, AuCu3-type cubic) forms congruently from c. In the Fe-Si system, the Fe-based facecentered cubic phase c is enclosed by a loop. The intermediate phases are: a2 (B2, CsCl-type cubic), a1 (D03, BiF3-type cubic), Fe2Si (stable between 1212 and 1040 C; hexagonal), Fe5Si3 (D88, Mn5Si3-type hexagonal), FeSi (B20-type cubic), bFeSi2 (tetragonal), and aFeSi2 (orthorhombic). There are a number of intermediate phases in the Ni-Si system: Ni3Si, Ni31Si12, Ni2Si, Ni3Si2, NiSi and NiSi2, with several of these having more than one crystal modiﬁcation. The phases that appear in the equilibria reviewed here are Ni3Si (L12, AuCu3-type cubic) and Ni31Si12 (labeled d; hexagonal). See [Massalski2] for the above phase diagrams.

Fig. 1 Fe-Ni-Si pseudobinary section along the Ni3Fe-Ni3Si join [2004Him]

Ternary Phase Equilibria With starting metals of 99.9% Fe, 99.9% Ni and 99.999% Si, [2004Him] induction-melted alloys with a constant Ni content of 75 at.%. The alloys were annealed between 900 and 500 C in the (c + c¢) and c¢ region. The phase equilibria were studied with optical and transmission electron microscopy and x-ray powder diffraction. The compositions of co-existing phases were determined by the electron probe microanalysis. Differential scanning calorimetry, electrical resistivity, and vibrating-sample magnetometry were also used to determine the phase equilibria and the Curie temperatures. The pseudobinary section along the Ni3Fe-Ni3Si join constructed by [2004Him] is shown in Fig. 1. The (c + c¢) region is broader in this system as compared to that in the Al-Fe-Si system. The Curie temperature of c¢ decreases with increasing Si content. With starting metals of 99.9% Fe, 99.9% Ni and 99.999% Si, [2005Him] induction-melted ternary alloys

Fig. 2 Fe-Ni-Si partial isothermal section in the Ni-rich region at 900 C [2005Him]

with Fe and Si in the range of 0-63 and 7-22 at.% respectively. The alloys were annealed between 900 and 700 C for durations up to 122 d. The partial isothermal sections constructed by [2005Him] at 900, 800 and 700 C are shown in Fig. 2-4. The homogeneity region of c¢ extends in a direction that lies between the Ni3Si-Ni3Fe join and the Ni3Si-Fe3Si join. The

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