The Co-Mn-Mo (cobalt-manganese-molybdenum) system

The Co-Mn system [Massalski 2] (Fig. 1) shows a peritectic reaction L + ( Mn) ↔ ( Mn) at ∼1185 °C and a eutectic reaction L ↔ ( Co) + ( Mn) at 1161 °C, where ( Co) is the face-centered-cubic (fcc) terminal solid solution of Co. The ( Mn) phase forms through a peritectoid reaction ( Mn) + ( Mn) ↔ ( Mn) at ∼1154 °C. A wide Mn phase field exists from Mn to the middle of the phase diagram. At 727 °C the Mn → Mn transformation occurs at the Mn side of the Co-Mn diagram. One intermediate phase CoMn forms through a peritectoid reaction ( Mn) + ( Co) ↔ CoMn at ∼545 °C. At the Co end of the Co-Mn system ( Co) → ( Co) phase transformation occurs at 422 °C where ( Co) is the hcp terminal solid solution of Co. The Co-Mo system [Massalski 2] (Fig. 2) has four intermediate phases Co9Mo2, Co3Mo, Co7Mo6 ( ) and of which the latter two phases form through peritectic reactions L + (Mo) ↔ at 1620 °C and L + ↔ at 1510 °C A eutectic reaction L ↔ + ( Co) occurs at 1335 °C. Three peritectoid reactions + ( Co) ↔ Co9Mo2, Co9Mo2 + ↔ Co3Mo and possibly ( Co) + Co3Mo ↔ ( Co) occur at 1200, 1025, and ∼700 °C, respectively. The Co9Mo2 and phases undergo eutectoid decomposition Co9Mo2 ↔ ( Co) + Co3Mo at 1018 °C and ↔ (Mo) + at 1000 ± 100 °C. The Mn-Mo system, which was calculated on the basis of a thermodynamic model [Massalski 2] (Fig. 3), shows equilibrium of ( Mn) with Mn (gas) above 2220 °C and below this temperature liquid Mn exists. Two intermediate phases, Mn5Mo4 and , exist in the Mn-Mo system and both of them form through peritectic reaction (Mo) + L ↔ Mn5Mo4 at ∼1500 °C and Mn5Mo4 + L ↔ at ∼1400 °C, the latter phase transforms eutectoidally ↔ Mn5Mo4 + ( Mn) at ∼1090 °C. At the Mn end the ( Mn) phase forms through a peritectic reaction L + ↔ Mn at ∼1300 °C and decomposes through a eutectoid reaction ( Mn) ↔ ( Mn) + ( Mn) at ∼1100 °C. The ( Mn) phase forms through a peritectoid reaction + ( Mn) ↔ ( Mn) at ∼1100 °C.