Numerical Simulation of the Simultaneous Precipitation of δ and γ′ Phases in the Ni‐Base Superalloy ATI Allvac®718Plus ^™

Abstract

The present work deals with the numerical simulation of the precipitation kinetics of δ (Ni 3 (Nb, Al)) and γ' (Ni 3 (Al, Ti, Nb)) phases in the commercial nickel-base superalloy ATI Allvac®718Plus TM . Important precipitate parameters such as volume fraction, mean radius and number density are numerically calculated as a function of the heat treatment parameters time and temperature and compared to experimentally determined data. To match the experimentally observed kinetics, the predicted interfacial energy of the precipitates, as calculated for a sharp, planar phase boundary, is adjusted to take into account the interfacial curvature and entropic effects of a diffuse interface. Using these modified interfacial energies, the calculated results show excellent agreement with the experimental measurements. Finally, a calculated time-temperature-precipitation (TTP) diagram for concurrent δ and γ' precipitation is presented, which clearly demonstrates strong kinetic interactions during simultaneous precipitation of these phases. Thus, the present study emphasizes the importance of carefully controlling the heat treatment parameters time and temperature during the production process of ATI Allvac®718Plus TM , in order to achieve the desired microstructure and hence mechanical properties.

Grain boundary precipitation in Inconel 718 and ATI 718Plus

“…However, discontinuities in the simulated T-T-T curves were observed at lower temperatures where precipitation of both γ′ and η phases occurs simultaneously. This has been attributed to a competition of the diffusional transport of elements that constitute both phases namely aluminium and niobium [34,66,67]. However, it would be of interest to obtain experimental volume fraction data at lower temperatures to see if these discontinuities can be validated.…”

Effect of Process Modeling on Product Quality of Superalloy Forgings

“…Figure 12 shows the results of several isothermal thermo-kinetic simulations and some experimental data of alloy Allvac®718Plus™ in a time temperature precipitation plot. More details regarding the method as well as further results of precipitation simulations of superalloys are presented in [28]. A coupling of these methods with finite element simulation of forging processes is possible but would result in not acceptable simulation times.…”

Morphology and Kinetics of Grain Boundary Precipitation in Alloy ATI 718Plus

“…The interest in alloy 718Plus has prompted the appearance of several studies tackling the same issue, although the information already available is naturally more limited. The precipitation kinetics of the strengthening phase y' has first been studied in terms of hardness [7,23] and later completed with TEM observations [23] and modeling simulations [5,24]. TTT diagrams of n/5 phase precipitation have been published both in solution-treated (strain free) [5,7] and forged [5,13,25] material.…”