The Ga-Mn-Ni (Gallium-Manganese-Nickel) System
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Phase Diagram Evaluations: Section II
The Ga-Mn-Ni (Gallium-Manganese-Nickel) System K. P. Gupta , The Indian Institute of Metals
The Ga-Mn-Ni system has attracted a lot of attention due to shape memory found for a Heusler-type GaMnNi2 alloy that is also ferromagnetic. However, very little work has been done on phase equilibria of the ternary system. The available information on the Ga-Mn-Ni system is reported here.
Binary Systems The Ga-Mn system [Massalski2] (Fig. 1) has eight intermediate phases, x (Ga4.6Mn), / (Ga3.3Mn), i (Ga2.3Mn), g (GaMn1.2 (LT)), k (GaMn1.2 (HT)), c2 (GaMn1.7), c3 (GaMn1.4), and e1 (GaMn2.5). Except for the e1 phase, which forms congruently from the facecentered cubic (fcc) c phase at 820 C, all the other phases form through peritectic or peritectoid reactions: L þ dMn $ k at 830 C, k þ c3 $ g at 600 C, L þ g $ / at 520 C, and L þ / $ x at 410 C. Several eutectic-type or eutectoid reactions occur in the Ga-Mn system: L $ ðGaÞ þ x at £29.8 C, k $ L þ g at 520 C, ðdMnÞ $ k þ c3 at 715 C, and c3 $ e1 þ ðbMnÞ at 620 C. The ðbMnÞ phase exists from ~80 to 100 at.% Mn at the higher temperatures, but at or below 727 C the aMn phase exists. The c3 , c2 , and c phase boundaries are not well determined. c is the fcc terminal solid solution ðcMnÞ. The Ga-Ni system [1991Nas] (Fig. 2) has eight intermediate phases, b1 (Ni3Ga), d0 ðNi5 Ga3 Þ, eðNi3 Ga2 (HT)Þ, c0 (Ni3Ga2 (LT)), m (GaNi), h (Ga4N3), b2 ðGa3 Ni2 Þ, and q (Ga4Ni), of which the m phase melts congruently at 1220 C. The b1 , b2 , q, and (Ga) phases form through peritectic reactions: c þ L $ b1 at 1212 C, L þ m $ b2 at 895 C, L þ b2 $ q at 363 C, and L þ q $ (Ga) at 30.2 C; the e, d0 , and h phases form through peritectoid reactions: b1 þ m $ e at 949 C, b1 þ e $ d0 at 741 C, and m þ b2 $ h at 542 C. The e $ c0 phase transformation occurs at ~680 C. A eutectic reaction L $ b1 þ m occurs at 1207 C. The Mn-Ni system [Massalski2] (Fig. 3) is a single peritectic system with the peritectic reaction L þ ðdMnÞ $ c occurring at 1164 C and has a liquidus/ solidus minimum of 1020 C occurring at ~38 at.% Ni. The cMn and Ni form a continuous solid-solution phase c. The c phase transforms to the m (MnNi (HT)), n (Mn2Ni (HT)), and f (MnNi2 (HT)) phases congruently at 911, 720, and K. P. Gupta, The Indian Institute of Metals, Calcutta, India; Contact e-mail: [email protected]
Note, that the diagram in Fig. 1 shows no two phase region between the single-phase region of the c, c2 , and c3 region. This implies higher order transitions. However, available data is not conclusive at this point.
710 C, respectively. Several other intermediate phases, f0 (MnNi2 (LT)), g1 (MnNi (MT)), g2 (MnNi (LT)), c1 (MnNi3), and j (Mn3Ni) phases, form through peritectoid reactions: c þ m $ g1 at 775 C, g2 þ c1 $ f0 at 440 C, ðaMnÞ þ c $ c1 at 520 C, ðaMnÞ þ c1 $ g2 at 480 C, and ðaMnÞ þ g2 $ j at 430 C. Several eutectoid reactions take place: m $ c þ g1 at 675 C, g1 $ n þ f at 620 C, f $ n þ c at 580 C, n $ ðaMnÞ þ c at 560 C, c $ g1 þ f at
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