Influence of transition group elements on the stability of theδ- andη-phase in nickelbase alloys

Abstract

To improve the high-temperature capability of 718-type wrought nickel-base superalloys, the γ-phase (Ni 3 Al) can be stabilized. However, this also reduces the size of the forging window because forging has to be done above the γ-and below the solvus temperature of the phase that is used to enable fine-grain forging, i. e. the δ-phase of Ni 3 Nb type or the η-phase of Ni 3 Ti-type. Understanding the influence of alloying elements on the formation of these phases is therefore important. In this paper, density functional theory calculations at 0K are performed to determine the stabilizing effect of aluminium and of the transition group elements on the stability of the δ-phase and η-phase. Most of the transition group elements of 5th and 6th period stabilize the δ-phase, whereas the stabilizing effect on the η-phase is weaker. According to the calculations, Mo, Tc, W, Re, and Os may be expected to stabilize the δ-phase but not the η-phase, whereas Al and Zn strongly stabilize the η-phase.

Effects of Alloying on the Interface Energy of the $$\gamma ''$$-Phase in Nickel-Based Superalloys

“…These calculations allow us to see whether these alloying elements prefer to stay in the c 00 bulk phase or at the interface. We also discuss the implication of our results, in connection with previous studies, [7,16] on the design of alloys where c 00 -strengthening is of interest.…”

“…[28,29] Together with our current results, this means that adding W would hinder the growth of c 00 -phase particles in the 100 direction: Any growth of the c 00 -phase particles would require the interface to carry these alloying atoms along. Moreover previous studies [7,15,16] have already shown that, in terms of the stabilization of the c 00 -phase, it is not advisable to add Mo and W since they possibly destabilize the c 00 -phase in favor of the d-phase.…”

On the Development Concept for a New 718-Type Superalloy with Improved Temperature Capability

“…As Nb is a particularly large atom, it significantly increases the lattice parameter of the γ -phase [33]. Replacing Fe with Co will reduce the lattice parameter of the γ-matrix at the same time, as Fe increases a γ while Co does not [34,35]. This may lead then to a positive γ/γ misfit, being large compared to values otherwise achieved in γ -strengthened wrought superalloys.…”

Understanding element solution energies in nickelbase alloys using machine learning

“…Understanding the influence of physical quantities on the stability of different phases is thus an important step in designing new alloys. Density functional theory (DFT) calculations can be employed for this, see for example [7,8] for the g¢-, [9] for the γ″-, and [10] for the δand η-phase.…”

“…We consider the four phases of composition Ni 3 A that are technically important: g¢, γ″, δ, and η. Data for the energy of the alloying elements in the γ″-, δ-, and η-phase are taken from [9,10], data for the g¢-phase were produced for this study. The aim is to find physical quantities that allow a prediction of the energy of the element in the Ni 3 A-phase.…”