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G. Zickler, R. Radis, R. Schnitzer, E. Kozeschnik, M. Stockinger, H. Leitner:
"The Precipitation Behavior of Superalloy ATI Allvac®718Plus";
Advanced Engineering Materials, 12 (2010), 176 - 183.

ATI Allvac 718Plus is a novel nickel-based superalloy, which was designed for heavy-duty applications in aerospace gas turbines. The precipitation kinetics of the intermetallic delta (Ni3Nb) and gamma' (Ni3(Al,Ti)) phases in this alloy are of scientific as well as technological interest because of their significant influence on the mechanical properties. Important parameters like grain size are controlled by coarse delta precipitates located at grain boundaries, whereas small gamma' precipitates are responsible for strengthening by precipitation hardening. In the present study, the microstructure is investigated by threedimensional atom probe tomography and simulated by computer modeling using the thermo-kinetic software MatCalc. The results of numerical simulations and experimental data are compared and critically discussed. It is shown that the chemical compositions of the phases change during isothermal aging, and the precipitation kinetics of d and gamma' phases interact with each other as shown in a time temperature precipitation (TTP) plot. The TTP plot shows C-shaped curves with characteristic discontinuities in the temperature range, where simultaneous and concurrent precipitation of the delta and gamma' phases occurs. This leads to a competition in the diffusion of Nb and Al, which are partly present in both phases. Thus, the present study gives important information on heat treatments for ATI Allvac 718Plus in order to achieve the desired microstructure and mechanical properties.

precipitation, delta, gamma', nickel-based superalloy, Allvac 718 Plus

http://dx.doi.org/10.1002/adem.200900282