Thermodynamic assessment of Co–Al–W system and solidification of Co-enriched ternary alloys

Cui, Yujie; Zhang, Xi; Xu, Guanglong; Zhu, Wenjun; Liu, H. S.; Jin, Zhanpeng

doi:10.1007/s10853-010-5115-y

Cited by 40 publications

(23 citation statements)

References 18 publications

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“…The Hessian of the Gibbs energy of the γ and γ' phases and the equilibrium composition of both phases have been computed from a recent thermodynamic database of the Co-Al-W system relying on the CALPHAD approach [46]. The nominal composition of the alloy as provided by EDS ( Thermodynamic equilibrium (tangent plane of G(C Al ,C W ) for both γ and γ' phases) leads to for the γ' phase.…”

Section: Nucleation and Growth Regimesmentioning

confidence: 99%

Kinetics pathway of precipitation in model Co-Al-W superalloy

et al. 2018

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Abstract:The early stages of precipitation of the γ ' phase in a model Co based superalloy (Co-9.1Al-7W (at.%)) have been investigated at 900 °C using electron microscopy and atom probe tomography. Nucleation, growth and coarsening stages have been studied with a focus on the temporal evolution of the precipitate composition in the light of recent theoretical developments on phase separation in multicomponent alloys. The experimental data have been confronted to the theories of nucleation and coarsening recently developed for such alloys, which are valid for non-ideal and non-dilute systems, and predict the temporal evolution of both the matrix and precipitate compositions. The rate constant for the mean size evolution of the particles, as derived from experiments, has been compared to the one predicted by the mentioned coarsening theory that accounts for a more accurate description of the thermodynamics of the phases, as compared with more classical approaches. From this comparison the γ/γ' interfacial energy was derived and found equal to ~48 mJ/m 2 . the exponents for the temporal evolution of average particles size, number of particles per unit volume were found identical to those for binary alloys during the coarsening regime, as expected, and the temporal evolutions of compositions in both γ and γ' phases were found to evolve as predicted by theory. Indeed, the W content in the particles, measured from atom probe tomography (APT) experiments, was found to significantly decrease with time and the observed evolution is remarkably well described by the theory and therefore is shown to originate from the competition between diffusion and capillarity.

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Section: Nucleation and Growth Regimesmentioning

confidence: 99%

Kinetics pathway of precipitation in model Co-Al-W superalloy

et al. 2018

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“…Several recent Calphad thermodynamic assessments have been performed assuming c¢ is an equilibrium phase at 900°C. [2,[7][8][9] Other work has focused on the mechanical properties of ternary and higher order alloys, [10][11][12][13][14][15][16][17] the evolution and coarsening behavior of two-phase c-c¢ microstructure, [13,15,[18][19][20] or the microstructure and partitioning behavior of quaternary and higher order alloying elements. [13,15,[21][22][23][24][25] Furthermore, the only experimental data available for temperatures other than 900°C are the 1000°C isothermal section presented by Sato et al [1] and data reported by Xue et al at 1300°C.…”

Section: Introductionmentioning

confidence: 99%

γ′ Phase Stability and Phase Equilibrium in Ternary Co-Al-W at 900 °C

Lass

Williams

Campbell

et al. 2014

J. Phase Equilib. Diffus.

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Phase equilibria at 900°C in the Co-rich Co-Al-W ternary system are investigated through isothermal annealing of six alloy compositions for times up to 8000 h. The volume fraction of the L1 2 -c¢ phase co-existing with disordered FCC-c, B2 and D0 19 phases is found to steadily decrease with increasing annealing time indicating that it is unstable at 900°C. Additional heat treatments at 850 and 1000°C further suggest it is a nonequilibrium phase at all temperatures in the ternary system. The L1 2 -c¢ phase dissolves slowly with significant amounts remaining in some alloys after 8000 h at 900°C. However, the present work clearly indicates the microstructure is moving toward a three-phase equilibrium between c, D0 19 , and B2. The collected compositional and phase equilibria information provide much needed data for improving the available thermodynamic assessments of the ternary Co-Al-W alloy system.

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“…Symbols represent experimental data of Dmitrieva [19] in Figure 4, and Shinagawa et al [20] in Figure 5. Solid curves are calculated using the present TCNI6, dashed ones by an earlier description present from TCNI4, and dotted ones by the recent description of Cui et al [21]. It can be seen in both figures that significant improvements are achieved with the present description.…”

Section: Thermodynamic and Kinetic Modelsmentioning

confidence: 79%

The Development and Validation of a New Thermodynamic Database for Ni-based Alloys ................................... 803

Bratberg¹,

Mao²,

Kjellqvist³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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Thermodynamic databases developed using the CALPHAD method has been successfully applied to the modeling and simulation of Ni based superalloys for more than fifteen years. Such databases when combined with suitable software, such as Thermo-Calc, can be used for accelerating alloy design as well as improving understanding of existing alloys in terms of their processing and in-service behavior. Additionally, such databases are also essential to the modeling of microstructural evolution using methods such as phase field or mean field approaches.A new thermodynamic database, TCNI6, has been developed for Ni-based superalloys based on the critical evaluation, using the CALPHAD method, of all the constituent binary systems across their full range of composition and many of the ternary systems containing Ni, as well as a number of other key ternary systems. The database has also been validated where possible against higher order systems as well.Together with the new mobility database, MOBNI3, which contains descriptions for the atomic mobility for respectively the γ (A1), γ' (L1 2 ), α (A2), β (B2) and liquid phases, TCNI6 can be used with software such as DICTRA to predict different kinetic aspects taking all relevant phases into account, e.g. the simulation of interdiffusion across Ni-based coatings.A new user friendly computational tool, TC-PRISMA, which simulates the kinetics of precipitation processes, is demonstrated utilizing these new databases and combined with interface property data. Engineering applications of precipitation modelling are validated against experimental data.

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Thermodynamic assessment of Co–Al–W system and solidification of Co-enriched ternary alloys

Cited by 40 publications

References 18 publications

Kinetics pathway of precipitation in model Co-Al-W superalloy

Kinetics pathway of precipitation in model Co-Al-W superalloy

γ′ Phase Stability and Phase Equilibrium in Ternary Co-Al-W at 900 °C

The Development and Validation of a New Thermodynamic Database for Ni-based Alloys ................................... 803

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