The phase equilibria in W-Fe-Co-Ni system alloys. II. Isotherms of the solidus and the phase composition of alloys containing 10 and 20% (Fe + Co + Ni) at temperatures above 1200°C

Conclusions

The isostructural intermediate μ-phases Fe₇W₅ and Co₇W₆ in the W—Fe—Co system form a continuous series of μ-solid solutions. In the 1640–1630°C range the L + α ⇄ μ(Fe₇W₆) peritectic equilibrium in this system changes to a similar L + α ⇄ μ(Co₇W₆) equilibrium, where α is the tungsten-base boundary solution.

In the W-Fe-Co-Ni polythermal tetrahedron in the 1470–1460°C range conversion of the L +α⇄μ(Fe₇W₆)+γ, peritectic equilibrium into the similar L + α ⇄ μ(Co₇W₆) + γ, where γ is the nickel-, γ-ironcobalt-base boundary solution, occurs.

Upon completion of crystallization at 1400°C, the W-Fe-Co system alloys with 10–20% (Fe + Co) have a α + μ phase composition, while the W-Fe-Co-Ni system alloys with 10–20% (Fe + Co + Ni) accordingly have α + μ, α + μ + γ or μ + γ. At temperatures below 1215°C in alloys rich in iron, FeW may be formed instead of μ-phase and therefore the alloys may have an α + FeW, α + μ + FeW, α + μ + γ + FeW and α + γ + FeW phase composition.