Phase Equilibria of the Co-Mo-Zr Ternary System at 1100 °C

Abstract

The isothermal section of the Co-Mo-Zr ternary system at 1100 °C was constructed experimentally. A series of phases including their crystal structures and compositions were obtained by examining the annealed specimens through x-ray diffraction (XRD), optical microscopy (OM), and electron probe microanalysis (EPMA). It was confirmed that two ternary phases, λ1 (Co0.5-1.5Mo1.5-0.5Zr, hP12-MgZn2) and Ƙ (CoMo4Zr9, hP28-Hf9Mo4B), exist in the Co-Mo-Zr ternary system at 1100 °C. And the experimental results also indicated that there are fourteen three-phase regions at 1100 °C. Ten of them were well determined in the present work: (1) (γCo) + Co11Zr2 + Co23Zr6, (2) (γCo) + Co23Zr6 + θ-Co9Mo2, (3) Co23Zr6 + θ-Co9Mo2 + μ-Co7Mo6, (4) (Mo) + μ-Co7Mo6 + Co2Zr, (5) (Mo) + Co2Zr + λ1, (6) (Mo) + Mo2Zr + λ1, (7) λ1 + Mo2Zr + CoZr, (8) Co2Zr + CoZr + λ1, (9) Mo2Zr + CoZr + liquid and (10) Ƙ + Mo2Zr + (βZr). The maximum solubilities of Zr in μ-Co7Mo6 phase, Mo in Co2Zr phase and Co in Mo2Zr phase were determined to be 5.89, 12.57 and 9.95 at.%, respectively. While the solubilities of Zr in θ-Co9Mo2 and (γCo) phases, Mo in Co11Zr2 and CoZr phases were detected to be extremely small. According to this work, the Co23Zr6 phase contained 21.61 at.% Mo and 8.32 at.% Zr. In addition, the maximum solubilities of Co and Zr in (Mo) phase and Mo in (γCo) phase were measured to be 3.61, 5.60 and 11.20 at.%, respectively.