The Co-Sn-Zr (Cobalt-Tin-Zircoium) System

Abstract

The Co-Sn binary system [1983Nis, Massalski2] (Fig. 1) has three intermediate phases: Co3Sn2 in two allotropic forms Co3Sn2 (g) above 500 C and Co3Sn2 (g1) below 500 C, CoSn (p) and CoSn2 (f). The g phase melts congruently at 1170 C and the other two phases form through peritectic reactions: L +gM p at 936 C and L + pM f at 525 C. Two eutectic reactions LM c + g and LM f + b occur at 1112 C and 229 C, respectively. The c and b phases are the terminal solid solutions of fcc aCo and of tetragonal bSn, respectively. The cM e transformation possibly occurs through a eutectoid type reaction at 420 C where e is the terminal solid solution of close packed hexagonal (cph) eCo. The Co-Zr system [Massalski2] (Fig. 2) shows the presence of five intermediate phases Co11Zr2 (w), Co4Zr ðiÞ, Co2Zr (k2), CoZr (b1), and CoZr2 (n). The probable presence of another phase CoZr3 (m) was reported but requires further confirmation. With the Co2Zr phase being an exception, all other phases are stoichiometric compounds. The Co2Zr, CoZr, and CoZr2 phase are believed to melt congruently at approximately 1620, 1420, and 1125 C, respectively. The w and i phases form through peritectic reactions: L + k2ML at 1452 C and Lþ i $ w at 1272 C. Four eutectic reactions occur in the Co-Zr system: LM c + w at 1222 C, LM k2 + b1 at 1312 C, LM b1 + n at 1061 C, and LM n + a at 981 C where a is the body centered cubic (bcc) terminal solid solution of bZr. A eutectoid reaction aM n + e2 occurs at 834 C where e2 is the cph terminal solid solution of aZr. In the Co-rich region possibly a eutectoid reaction cMw + e1 occurs at 422 C. The Sn-Zr system [Massalski2] (Fig. 3) has three intermediate phases, SnZr4 (h), Sn3Zr5 (x), and Sn2Zr (/) of which the x phase melts congruently at 1988 C. The probable existence of another phase Sn4Zr5 (T) has been suggested in the SnZr system. The h and / phases form through peritectoid and peritectic reactions: x + aM h at 1327 C and L + xM/ at 1142 C. The reaction through which the T phase forms is not known. Two eutectic reactions LM a + x and LM/ + b occur at 1592 and 232 C, respectively. The cph e2 phase forms through a peritectoid reaction a + hM e2 at 982 C where e2 is the cph terminal solid solution aZr.