Numerical simulations of phase separation in Fe-Cr-Ni ternary alloys and Fe-Cr-Mo-Ni quaternary alloys similar to ferrite phases in duplex stainless steels were performed with using of the Cahn-Hilliard equations. A new numerical model based on the Gauss-Seidel and Newton-Raphson methods were utilized to obtain efficient and accurate solution.We obtained that small addition of Ni retard phase separation of Cr in Fe-Cr-Ni ternary alloys. The simulation results on behavior of Mo and Ni in Fe-Cr-Mo-Ni ternary alloys were quite similar to Mo in Fe-CrMo and Ni in Fe-Cr-Ni ternary alloys. It is known that behavior of Mo or Ni along the trajectory of the peak tops of Cr concentration is determined by the sign of second derivative of Cr and Mo or which of Cr and Ni. The effect of Ni on the peak height of Cr in Fe-Cr-Mo-Ni quaternary alloys is similar to which in FeCr-Ni alloys.Numerical simulation results on the variation of peak height of Cr are qualitatively in good agreement with those obtained by the Atom-Probe-FIM.
Alloy 718 rotors, in previously unheard of sizes, have been introduced into GE heavy-duty gas turbines. The forged area of each disk in a rotor is an order of magnitude larger than those of aircraft engine disks. The production challenges posed by the very large 718 ingots and forgings needed to make the rotors are discussed in this paper. The issues include segregation, abnormal grain growth and processing limitations imposed by the size of production equipment.
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