Phase Equilibria of the Co-Mo-Zr Ternary System at 1000 °C

The isothermal section of the Co-Mo-Zr ternary system at 1000 degrees C was investigated by using 29 alloys. The annealed alloys were examined by means of x-ray diffraction, optical microscopy, and electron probe microanalysis. It was confirmed that three ternary phases, lambda (1) (Co0.5-1.5Mo1.5-0.5Zr, hP12-MgZn2), omega (CoMoZr4) and kappa (CoMo4Zr9, hP28-Hf9Mo4B), exist in the Co-Mo-Zr ternary system at 1000 degrees C. And the experimental results also indicated that there are sixteen three-phase regions at 1000 degrees C. Thirteen of them were well determined in the present work: (1) (gamma Co) + Co11Zr2 + Co23Zr6, (2) (gamma Co) + Co23Zr6 + epsilon-Co3Mo, (3) Co23Zr6 + epsilon-Co3Mo + mu-Co7Mo6, (4) (Mo) + mu-Co7Mo6 + Co2Zr, (5) (Mo) + Co2Zr + lambda (1), (6) (Mo) + Mo2Zr + lambda (1), (7) lambda (1) + Mo2Zr + CoZr, (8) Co2Zr + CoZr + lambda (1), (9) Mo2Zr + CoZr2 + omega, (10) kappa + Mo2Zr + omega, (11) CoZr2 + liquid + omega, (12) (beta Zr) + liquid + omega and (13) (beta Zr) + kappa + omega. The homogeneity of lambda (1) spans in the range of 28.66-50.77 at.% Co and 15.71-37.03 at.% Mo, and that for omega is within the range of 18.66-23.64 at.% Co and 8.53-14.68 at.% Mo. The homogeneity range for kappa is from 8.09 at.% to 9.94 at.% Co and 23.13 at.% to 25.58 at.% Mo. The maximum solubility of Zr in mu-Co7Mo6 phase, Mo in Co2Zr phase and Co in Mo2Zr phase were determined to be 6.17, 11.27 and 9.14 at.%, respectively. While the solubility of Zr in epsilon-Co3Mo and (gamma Co) phases, Mo in Co11Zr2 and CoZr phases were detected to be extremely small. According to this work, the Co23Zr6 phase contained 15.61 at.% Mo and 12.7 at.% Zr. In addition, the maximum solubility of Co and Zr in (Mo) phase and Mo in (gamma Co) phase were measured to be 3.50, 5.44 and 7.40 at.%, respectively.