A thermodynamic database for Ni‐base superalloys

Abstract

A thermodynamic database has been developed for Ni‐base superalloys. Following the CALPHAD procedure, it is based on the assessment of thermodynamic behaviour of the relevant constituting sub‐systems of the complex system of interest. The current database contains 7 elements: Al, Co, Cr, Ni, Ti, W, Re. The thermodynamics of the γ and γ′ phases are modelled with a single Gibbs energy function taking into account the crystallographic relation between these two phases. The formalism of the thermodynamic models used is briefly introduced. A few phase diagrams calculated with the current database in assessed binary and ternary systems are presented. Some experiments available in higher order systems are compared with the results of calculations with the current database. The ability of extrapolation of the database is verified for solid state equilibria as well as for solidification behaviour (liquidus temperature and partition ratios). The introduction of Mo and Ta to the current database is in progress. Other elements (Nb, Fe, Zr, Hf, C, B, ···) are planed to be introduced.

On the diffusion mechanisms of fine-scaleγ′ in an advanced Ni-based superalloy

“…For the more complex case of RR1000 nickel-based superalloy, the chemistry of the γ phase is generally given as (Ni, Co, Cr, Mo) 3 (Al, Ti, Ta, Hf. The elements Al, Ti, Ta and Hf, are generally assumed to substitute into the β-sublattice, while Ni, Co, Cr, and Mo occupy the α-sublattice as predicted by first principle calculations [20][21][22][23][24][25]. Herein Hf is not found to be present at measurable levels in the precipitate size range considered in this work.…”

Polycrystalline &gamma(Ni)/&gamma'(Ni₃AI)-δ(Ni₃Nb) Eutectic Ni-base Superalloys: Chemistry, Solidification and Microstructure

“…Many of the commercially available thermodynamic software models have been demonstrated to be quite reliable in predicting phase stability and volume fractions in traditional !/!" Ni-base superalloys [33][34][35], where significant amounts of high fidelity experimental data were used to validate the free energy curves. When these thermodynamic models are extended to multicomponent !/!…”

“…"-# eutectic alloys might have contributed to the observed differences. To successfully predict the properties of equilibrium phase in an alloy system, the free energy curves assigned to each constituent phase needs to accurately describe its thermodynamic properties [33][34][35]. The observed discrepancies can likely be attributed to the relatively limited amount of thermodynamic information of higher order Nb-containing subsystems that exists within the thermodynamic database.…”

Diffusion in FCC Co-rich Co-Al-W Alloys at 900 and 1000 °C

“…To study the diffusion mobilities in the Co-Al-W system in the single-phase FCC region, diffusion couples were [25,26] w/ thermodynamics [27] Gomez-Acebo (Al-Co-Cr-Ni-Ti) [24] w/ thermodynamics [34] Chang and…”