The Co−Ge−Mo (Cobalt-Germanium-Molybdenum) system

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The Co-Ge system [Massalski2] (Fig. 1) shows the presence of six intermediate phases: Co3Ge, Co5Ge2, Co5Ge3, CoGe, Co5Ge7, and CoGe2, of which the Co5Ge3 phase exists in two polymorphic forms, the high-temperature Co5Ge3 and the low-temperature (T < 382 °C) Co5Ge3 phases. The Co5Ge3 phase melts congruently at 1210 °C. Alloying Co with Ge stabilizes the hexagonal close packed (hcp) ( Co) phase to quite high temperatures. The ( Co), CoGe, and CoGe2 phases form through peritectic reactions: L + ( Co) ↔ ( Co), L + Co5Ge3 ↔ CoGe, and L + CoGe ↔ CoGe2 at 1123, 985, and 832 °C, respectively. The Co3Ge, Co5Ge2, and Co5Ge7 phases form through peritectoid reactions: ( Co) + Co5Ge3 ↔ Co3Ge at ∼770 °C; ( Co) + Co5Ge3 ↔ Co5Ge2 at 636 °C; and CoGe + CoGe2 ↔ Co5Ge7 at 806 °C. The Co3Ge and Co5Ge2 phases exist only at the higher temperatures and transform through eutectoid reactions: Co3Ge ↔ ( Co) + Co5Ge3 at temperatures above 836 °C and Co5Ge2 ↔ ( Co) + Co5Ge3 at temperatures 382 °C. Two eutectic reactions, L ↔ ( Co) + Co5Ge3 and L ↔ CoGe2 + (Ge), occur at 1108 and 817 °C, respectively. The Co-Mo system [Massalski2] (Fig. 2) shows the presence of four intermediate phases: Co9Mo2, Co3Mo, Co7Mo6 ( ); and . The and phases form through the 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 probably ( Co) + Co3Mo ↔ ( Co), occur at 1200, 1025, and ∼700 °C, respectively. The Co9Mo2 and phases transform through eutectoid reactions Co9Mo2 ↔ ( Co) + Co3Mo and ↔ (Mo) + at 1018 and ∼1000 °C, respectively. The Ge-Mo system [1987Ole, Massalski2] (Fig. 3) has four intermediate phases: Ge2Mo; Ge23Mo13; Ge3Mo; and GeMo3. A metastable Ge2Mo phase forms on rapid quenching of alloys containing <40 at.% Mo from 1350 °C. The Ge2Mo phase, however, is a stable phase above 20 kbar pressure, and only after annealing in a vacuum at 1000 °C for 5 h does the Ge2Mo phase transform into the Ge2Mo phase. All of the intermediate phases form through peritectic reactions: L + (Mo) ↔ GeMo3 at 1800 °C;