The Co-Ni-Y (Cobalt-Nickel-Yttrium) System

The Co-Ni system [Massalski2] (Fig. 1) is a simple isomorphous system with solidus and liquidus lines very close to each other. The solid solution, face centered cubic (fcc) c phase, extends from fcc aCo to Ni. At the Co-end, at temperatures 1300 C and p¢ at <1300 C), Co5Y (x), Co7Y2 (q), Co3Y (m), Co2Y (k2), Co3Y2 (f), Co 7Y 6 (s), CoY (h¢), Co3Y4 (d), Co5Y8 (i), CoY3 (g). A metastable phase Co2Y3 (/¢) has been reported in the Co-Y system. The p and x phases melt congruently at 1357 and 1345 C, respectively. All other phases form through peritectic or peritectoid reactions: Lþ x $ q at 1320 C, Lþ q $ m at 1308 C, Lþ m $ k2 at 1154 C Lþ k2 $ f at 866 C, Lþ f $ h0 at 798 C, Lþ h0 $ i at 740 C, Lþ e0 $ g at 889 C, h0 þ f $ s at 775 C, and i þ h0 $ d at 732 C. Three eutectic reactions L $ c þ p, L $ p þ x, and L $ i þ g occur at 1340, 1300, and 738 C. The Ni-Y system [Massalski2] (Fig. 3) has nine intermediate phases, Ni17Y2 (p), Ni5Y (x), Ni4Y (w), Ni7Y2 (q), Ni3Y (m), Ni2Y (k2), NiY (h), Ni2Y3 (/), and NiY3 (g), of which the x and h phases melt congruently at 1430 and 1070 C, respectively. All other phases form through peritectic reactions: Lþ x $ p at 1330 C, Lþ x $ w at 1340 C, Lþ w $ q at 1298 C, Lþ q $ m at 1237 C, Lþ m $ k2 at 1106 C, Lþ h $ / at 820 C, and Lþ e0 $ g at 902 C. Three eutectic reactions, L $ c þ p; L $ k2 þ h, and L $ / þ g occur at 1285, 950, and 805 C, respectively. e¢ is the cph terminal solid solution of ac.