The Co-Ni-Si (Cobalt-Nickel-Silicon) System

Abstract

The Co-Ni system [Massalski2] (Fig. 1) is a simple isomorphous system with liquidus and solidus temperatures very close to each other. The face centered cubic (fcc) solid solution of (aCo, Ni), designated here as c phase, possibly has a short range ordering reaction at the CoNi3 composition. At the Co-end, the fcc aCo transforms to close packed hexagonal (cph) eCo phase at T 422 C: The Co-Si system [Massalski2] (Fig. 2) has five intermediate phases, Co3SiðiÞ; aCo2SiðdÞ; bCo2SiðqÞ;CoSiðgÞ; and CoSi2 (f), of which the bCo2Si, CoSi, and CoSi2 phases melt congruently at 1334, 1460, and 1326 C; respectively. The Co3Si and aCo2Si phases form through peritectic reactions, L + d$ i at 1214 C and L + qM d at 1320 C: The cph (eCo) phase is stabilized to higher temperatures with addition of Si to Co and at 1250 C a peritectic reaction, L + (aCo)M (eCo), occurs. The Co3SiðiÞ and bCo2Si (q) phases exist only at higher temperatures and decompose through eutectoid reactions, i $ ðeCoÞ þ d at 1193 C and qM d + g at 1286 C. The four eutectic reactions L $ ðeCoÞ þ i;L $ q þ g;L $ g þ f; and LM f + (Si) occur at 1204, 1286, 1310, and 1259 C; respectively. The CoSi2 phase is of invariant composition. The Ni-Si system [Massalski2] (Fig. 3) has eight intermediate phases, Ni3Si (b1), Ni3Si (b2 and b3), Ni31Si12ðcÞ;Ni2SiðdÞ;Ni2SiðhÞ;Ni3Si2ðe and e0Þ;NiSiðnÞ; and NiSi2ðf and f0Þ; of which several phases, b2 and b3, e and e0 and f and f0; exist in polymorphic forms with polymorphic transformation temperatures of 1115, 830, and 981 C; respectively. The b1, b3, d, e¢, and f0 phases form through peritectic or peritectoid reactions: Lþ c0 $ b3 at 1178 C, L + hM d at 1255 C;Lþ ðSiÞ $ f0 at 993 C; ðNiÞ þ b2 $ b1 at 1035 C; and h + nM e¢ at 845 C: There are eight eutectic or eutectoid reactions in the Ni-Si system: LM (Ni) + b3 at 1145 C;L $ c0 þ d at 1215 C, L $ h þ n at 964 C, L $ n þ f at 966 C; b2 $ b1 þ c0 at 990 C; h $ d þ e0 at 825 C; e0 $ d þ e at 820 C; and e0 $ e þ n at 800 C: The c0; d; n and f phases are single composition phases.