Ab initio calculations of elastic properties of Ru1−xNixAl superalloys (original) (raw)
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Ab initio calculations of elastic properties of Ru[sub 1−x]Ni[sub x]Al superalloys
Applied Physics Letters, 2009
Ab initio total energy calculations based on the exact muffin-tin orbitals method, combined with the coherent potential approximation, have been used to study the thermodynamical and elastic properties of substitutional refractory Ru 1−x Ni x Al alloys. We have found that the elastic constants CЈ and C 11 exhibit pronounced peculiarities near the concentration of about 40 at. % Ni, which we ascribe to electronic topological transitions. Our suggestion is supported by the Fermi surface calculations in the whole concentration range. Results of our calculations show that one can design Ru-Ni-Al alloys substituting Ru by Ni ͑up to 40 at. %͒ with almost invariable elastic constants and reduced density.
Superalloys 2008 (Eleventh International Symposium), 2008
Refractory elements are used in Ni-based superalloys to increase creep resistance (Mo, Re, W) and to retard the coarsening of the γ' phase (Re). At high concentrations of refractory elements precipitation of topologically closepacked (tcp) phases [1] is detrimental to the creep properties of the alloys. A more detailed understanding of the formation kinetics and thermodynamic stability of tcp phases will therefore be beneficial for the design of the next generation superalloys. Atomistic modeling of tcp stability with interatomic potentials requires to go beyond the second-moment approximation to the electronic density of states by including up to at least the sixth moment [2]. We have developed an analytic bond-order potential (BOP) that systematically takes into account higher moment contributions to the density of states and depends explicitly on the valence of the transition-metal elements [3]. For the parameterization of the new BOP, we performed extensive density functional theory (DFT) calculations of elemental and binary compound phases of Ni, the technologically important alloying element Cr, and the refractory metals Mo, Re, and W. We will discuss the structural trends of the DFT calculations, compare to the predictions of the analytic BOP and report on our progress on the parameterization of the analytic BOP for the Re-W system. This work is part of the EPSRC-funded collaborative multi-scale project 'Alloys by Design'.
Computational Study of A15 Ru-Based Alloys for High-Temperature Structural Applications
Ruthenium - an Element Loved by Researchers [Working Title], 2021
The structural, magnetic, electronic and elastic properties of A15 X3Ru (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) binary alloys are investigated using first-principles density functional theory (DFT) methods. Ru-based alloys have attracted remarkable research interest due to their unique properties, which make them suitable for high-temperature structural applications. In this chapter, the properties of several A15 Ru-based alloys are investigated in order to select the best suitable alloy/s for aerospace application. Heats of formation are calculated to determine the thermodynamic stability of the materials. Knowledge of the values of elastic constants is essential for understanding the mechanical properties of the materials. From our calculated elastic constants, the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, melting temperature, anisotropic factor and the ratio B/G are determined. The electronic density of states are calculated and discussed. Lastly, the ...
First principles study of structural, electronic and mechanical properties of ternary Ru-Cr-X alloys
2017
We have investigated the effect of doping on the structural, electronic and mechanical properties of A15 RuCr3 and A15 Ru3Cr alloys using density functional theory. Various transition metal dopants, namely V, Mn, Fe, Co, Zr, Mo, Pd, Pt and Re were introduced in the 2x2x2 supercells constructed from the optimized unit cells of RuCr3 and Ru3Cr binary alloys. The calculated lattice constants for the pure metals, doped and undoped Ru48Cr16 and Cr48Ru16 alloys were determined using the generalized gradient approximation. The results are in overall good agreement with the experimental and previous theoretical data. The relaxed lattice constants for the X doped Ru48Cr16 and Cr48Ru16 structures (X = V, Mn, Fe, Co, Zr, Mo, Pd, Pt and Re) remained the same as the unrelaxed structures because the supercells were produced from the optimized unit cells. All the studied undoped systems were predicted to be unstable, in agreement with the previous theoretical study. Stability of doped Ru48Cr16 and...
Journal of Applied Physics, 2012
Due to their high strength and advantageous high-temperature properties, tungsten-based alloys are being considered as plasma-facing candidate materials in fusion devices. Under neutron irradiation, rhenium, which is produced by nuclear transmutation, has been found to precipitate in elongated precipitates forming thermodynamic intermetallic phases at concentrations well below the solubility limit. Recent measurements have shown that Re precipitation can lead to substantial hardening, which may have a detrimental effect on the fracture toughness of W alloys. This puzzle of subsolubility precipitation points to the role played by irradiation induced defects, specifically mixed solute-W interstitials. Here, using first-principles calculations based on density functional theory, we study the energetics of mixed interstitial defects in W-Re, W-V, and W-Ti alloys, as well as the heat of mixing for each substitutional solute. We find that mixed interstitials in all systems are strongly attracted to each other with binding energies of À2.4 to À3:2 eV and form interstitial pairs that are aligned along parallel first-neighbor h111i strings. Low barriers for defect translation and rotation enable defect agglomeration and alignment even at moderate temperatures. We propose that these elongated agglomerates of mixed-interstitials may act as precursors for the formation of needle-shaped intermetallic precipitates. This interstitial-based mechanism is not limited to radiation induced segregation and precipitation in W-Re alloys but is also applicable to other bodycentered cubic alloys.
2016
Abstract. It is well established that Re and Ru additions to Ni-base superalloys result in improved creep performance and phase stability. However, the role of Re and Ru and their synergetic effects are not well understood, and the first step in understanding these effects is to design alloys with controlled microstructural parameters. A computational approach was undertaken in the present work for designing model alloys with varying levels of Re and Ru. Thermodynamic and first principles calculations were employed complimentarily to design a set of alloys with varying Re and Ru levels, but which were constrained by constant microstructural parameters, i.e., phase fractions and lattice misfit across the alloys. Three ternary/quaternary alloys of type Ni-Al-xRe-yRu were thus designed. These compositions were subsequently cast, homogenized and aged. Experimental results suggest that while the measured volume fraction matches the predicted value in the Ru containing alloy, volume fract...
Computational design of model Re/Ru bearing Ni-base superalloys
It is well established that Re and Ru additions to Ni-base superalloys result in improved creep performance and phase stability. However, the role of Re and Ru and their synergetic effects are not well understood, and the first step in understanding these effects is to design alloys with controlled microstructural parameters. A computational approach was undertaken in the present work for designing model alloys with varying levels of Re and Ru. Thermodynamic and first principles calculations were employed complimentarily to design a set of alloys with varying Re and Ru levels, but which were constrained by constant microstructural parameters, i.e., phase fractions and lattice misfit across the alloys. Three ternary/quaternary alloys of type Ni-Al-xRe-yRu were thus designed. These compositions were subsequently cast, homogenized and aged. Experimental results suggest that while the measured volume fraction matches the predicted value in the Ru containing alloy, volume fraction is significantly higher than the designed value in the Re containing alloys. This is possibly due to errors in the thermodynamic database used to predict phase fraction and composition. These errors are also reflected in the mismatch between predicted and measured values of misfit.
Reasons for the enhanced phase stability of Ru-containing nickel-based superalloys
Acta Materialia, 2011
Improvements in phase stability on the addition of Ru are well known in the field of nickel-based superalloy development. However, the key mechanism of this benefit remains unclear. A new alloy series with stepwise increased additions of Ru was used to systematically investigate the impact of Ru on yopologically close-packed (TCP) phase inhibition. In addition, the investigation was carried out on a less known type of TCP formation, the so-called discontinuous precipitation. This type of TCP phase formation offers two major advantages compared with commonly investigated TCP plates in dendritic regions. First, the microstructure is much coarser than fine TCP plates, allowing reliable and less time consuming investigations. Second, discontinuous precipitation transforms the supersaturated and unstable c/c 0 microstructure in a condition close to equilibrium, permitting a meaningful insight into the stable alloy constitution. The experimental results for alloy phase stability dependence on Ru are evaluated with respect to all possible effects of TCP phase inhibition by Ru. Furthermore, experimental evidence for increased Re solubility in the c matrix was found on addition of Ru, which is not seen in corresponding ThermoCalc calculations. This finding is probably the dominant reason for the increased TCP phase capability of Ru-containing alloys. A ternary phase diagram model has been developed to describe the new approach.
The precipitation of topologically close packed (TCP) phases is detrimental for the high temperature strength of high refractory Ni-based superalloys. The beneficial influence of Ru with respect to this so called instability is nowadays well accepted. In the present paper the precipitation of topologically close packed (TCP) phases is studied quantitatively in two experimental alloys (one Ru-free and one with addition of Ru) to clarify the mechanism of the Ru effect. It is confirmed that the TCP phase precipitates undergo sequential phase transformation with the tetragonal r-phase precipitating first. Ru retards the phase transformation and leads to decreased equilibrium volume fraction of TCP phases. The results clearly indicate that Ru decreases the driving force for TCP phase precipitation. Investigations of crystallography and chemistry of the TCP/matrix interface point to an additional effect by increase of misfit strain energy.
Acta Materialia, 2008
The Ni-Ru and Al-Ni-Ru systems are assessed with a combined CALPHAD and ab initio approach. Particular attention is paid to the possible existence of a miscibility gap in the B2 phase. Both face-centered cubic and body-centered cubic ordering are analyzed within the compound energy formalism. Ab initio calculations for the B2 phase show a similar trend as calorimetric measurements but the magnitude is much smaller. It is found that the calorimetric measurements cannot be reconciled with any reasonable phase diagram, whereas the ab initio results can. From the parameters obtained, isothermal sections in reasonable agreement with experimental phase diagrams are calculated. We have concluded that there is no miscibility gap in the B2 phase at 1273 K and higher temperatures.