Thermodynamic modeling of Al–Co–Cr, Al–Co–Ni, Co–Cr–Ni ternary systems towards a description for Al–Co–Cr–Ni

Abstract

the modeling of the subsystems, especially Al-Co-Ni and Co-Cr-Ni, necessary in building a coherent Al-Co-Cr-Ni quaternary description. Some modifications are made in the description of the Al-Co-Cr [5] system and are discussed in detail later in the manuscript. The quaternary Al-Co-Cr-Ni system is studied in a separate publication [8].While B2 (β, , simple cubic type) and fcc-A1 (γ, , disordered f.c.c.) are the desired phases in MCrAlY coatings, all other phases must be modeled to give an accurate overall description of phase stability in the system. These include bcc-A2 (α, , disordered b.c.c.), 3 Pm m 3 Fm m 3 Im m 3 hcp-A3 (ε, , disordered h.c.p.), L1 2 (γ', , simple cubic type), sigma (σ, , Frank-Kasper, Figure 1 (a)) and the binary intermetallics. The present paper focuses on evaluating and modeling the important ternary alloy systems found in the Al-Co-Cr-Ni quaternary in order to produce meaningful extrapolations without the need of excessive higher order parameters. First-principles calculations based on density functional theory (DFT) are performed to supplement the lack of experimentally measured thermochemical data. By effectively combining these results with experimental information from the literature, energetically accurate parameters in the lower order systems are evaluated. Ultimately, this model will be used in the construction of a multicomponent Al-Co-Cr-Ni database in future work. 2 Literature review 2.1 Binary models used in the present workThe assessment of the Al-Co binary by Dupin and Ansara [9] reproduces all experimental results available in the literature satisfactorily and is hence adopted in the present work. The model for B2 in the original Al-Co binary was asymmetrical and was changed to the orderdisorder model by Liu et al. in previous work on the system [5], which is adopted here. The Al-Cr assessment by Saunders, which can be found in the COST507 [10] database, is also accepted without modification. The assessment for the Al-Ni binary by Ansara et al. [11], (later modified by Dupin et al. [6]) has been used extensively previously and is, therefore, adopted in the present work. There are two descriptions of the Co-Cr binary available which both reproduce certain experiments well, one by Oikawa et al. [12] and another by Kusoffsky et al. [13]. However, it 3 6/ P mmc 3 Pm m 2 4/ P mnm 4 has been found that the Oikawa description has σ end-member energies which disagree with experiments by Downie and Arslan [14] though it was adopted in the previous modeling of Al-Co-Cr [5]. It is important to have correct energies in the binary subsystems to produce accurate extrapolations to the higher order systems and for this reason, the model by Kusoffsky et al. [13] is used here. The Co-Ni and Cr-Ni binary descriptions are taken from SGTE [15], based on works by Guillermet [16] and Lee [17], respectively. In addition, the present Cr-Ni description includes a metastable description of σ following the work by Gustafson [18] in the ternary Ni-Cr-W system which is later modified by Kattner [7]. Re...

Modes of Deposit-Induced Accelerated Attack of MCrAlY Systems at 1100 °C

“…All phase equilibrium calculations were done for T = 1100 • C, using the NIST database [28] in Thermo-Calc [29]. The later use of CRALDAD, a more recent database specifically developed for the Al-Co-Cr-Ni system [30,31], showed that the alloys were in fact slightly off the tie-lines; nevertheless, the principle of independently varying phase fractions and phase compositions is still qualitatively valid. For clarity of reading, the alloys will be referred to using their β fraction (vol.…”

Kinetics of Al2O3-Scale Growth by Oxidation and Dissolution in Molten Silicate

“…As a test of the latter aspect, concentration profiles in the single-phase γ alloys Ni-28Co-19Cr-11Al-0.1Y and Ni-33Co-35Cr-7Al-0.1Y oxidized with and without deposit were simulated in Dictra, using the experimentally measured interfacial and bulk concentrations as boundary conditions. The diffusivities were computed from the CRALDAD thermodynamic database, which was optimized for high Co and Cr levels in the NiCoCrAl system [17,18], and the MobNi1 [19] and NIST Ni Superalloy [20] mobility databases (both gave similar results). In all cases, the simulated profiles matched the experimental profiles less well than when using an effective D a Al (the computedD Ni Al,Al values were higher than our D a Al values by a factor of 10).…”

Design of Eutectic High Entropy Alloys in Al–Co–Cr–Fe–Ni System

“…For Al-Co-Cr system neither a liquidus projection nor a minimum eutectic composition is reported. However, Liu et al [33] modeled the isothermal section of Al-Co-Cr system at 1300 °C, and from the isothermal section, the boundaries of the two phase region γ+B2 can be obtained ( Figure 1e). According to the boundaries of the two phase region γ+B2 at 1300 °C, the eutectic line could be predicted which is shown in Figure 1e.…”