Thermodynamic remodeling of the Al–Pt system towards an assessment of the Al–Ni–Pt system

Abstract

The thermodynamic CALPHAD description of the Al-Pt system is remodeled. The four sub-lattice (4SL) model for the ordered/disordered fcc and bcc phases is adopted resulting in improved agreement with experiment and first-principles information compared to previous descriptions. First-principles calculations are performed and the results are used in addition to available experimental data as input for the modeling. Modeling results agree well with most experimental phase equilibria and thermochemical data compiled. Special attention is also paid to the metastable phase diagrams to ensure that the parameters obtained in the modeling do not present unphysical results in the metastable regime. The obtained fcc and bcc descriptions are converted to two sublattice (2SL) models to enable combination with available multi-component Ni-base superalloy descriptions. The converted Al-Pt system is extended into the Al-Ni-Pt ternary system to study its extrapolation characteristics using available thermodynamic and thermochemical data. It is found that the 2SL model is not adequate in capturing the thermodynamic behavior of the fcc-based phases found in the ternary Al-Ni-Pt system. Possible approaches for future work is discussed.

Phase Stability, Structure and Thermodynamics of Modified Ni- and Fe-Aluminides

“…Importantly, they form a wide two-phase region with respective fcc-Ir(Al) and Ru(Al) solid solution phases. However, in the case of Al-Pt, three Ptrich Al 3 Pt 5 , AlPt 2 and L1 2 -AlPt 3 phases are present owing to which no two-phase region (AlPt+Pt(Al)) appears stable [45][46][47]. The phase fields of L1 2 -based γ′-Ni 3 Al and AlPt 3 get separated by an ordered L1 0 -based ternary compound α-NiAlPt 2 , designated as γ* in few studies [48].…”

“…The change in solid-solubility limits of technologically relevant phases, namely γ, γ′ and β with temperature needs to be assessed to optimize the heat-treatment and service conditions. The phase fields are based on the calculated isothermal sections utilizing the thermodynamic assessment of Liu et al [45] as projected in Fig. 18 at 1000 °C (1273 K) and 1200 °C (1473 K).…”

“…For a lucid view on the demarcation of various phase-field regions, the following isotherms have been plotted with a focus on the Ni-Cr rich region with Al<40 at.% in Figs. 45. [123] and (e) comparison on the homogeneity ranges of γ and γ′ at different temperatures.…”

“…Since, the Ni-rich β-NiAl bond coat is more relevant from the application point of view, the variation of thermodynamic factor of Ni in Ni-rich aluminide alloy has been plotted as a function of Pt, Cr and Fe in Fig. 62 utilizing the assessed parameters of [45,88,132] respectively. It is interesting that Ni has a higher diffusion rate than Al in the Ni-rich NiAl phase [4], therefore Φ Ni,Ni is considered for comparison.…”