Atom-probe microanalysis of a nickel-base superalloy

Blavette, D.; Bostel, A.; Sarrau, J.M.

doi:10.1007/bf02670358

Cited by 51 publications

(12 citation statements)

References 22 publications

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“…Low atomic density zones are due to defocusing effects. W is known to be a high evaporation field element [32]. Consequently, W-enriched precipitates have a higher evaporation field compared to that of the surrounding γ matrix.…”

Section: Methodsmentioning

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: Methodsmentioning

confidence: 99%

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

et al. 2018

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“…In addition, the concentration profiles have to be convoluted by a Gaussian function with a full width at half maximum of~1 nm, [27] which partly takes into account trajectory aberrations and local magnification effects. [28,29] The concentration profiles are flat in c¢ and wavy in c in HC sample. Of particular interest is its diffuse interface between c and c¢ phase.…”

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confidence: 95%

Spinodal Decomposition Mechanism of γ′ Precipitation in a Single Crystal Ni-Based Superalloy

Tan¹,

Mangelinck²,

Perrin-Pellegrino³

et al. 2014

Metall Mater Trans A

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The precipitation of c¢ phase in a commercial single crystal Ni-based superalloy with different cooling rates has been investigated by atom probe tomography. Numerous irregular interconnected c¢ precipitates in the size range of~30 to 50 nm were obtained even utilizing the fastest possible cooling rate. Diffuse c/c¢ interface and far from equilibrium composition of c¢ phase were observed in the fast-cooled sample, suggesting that c¢ precipitation occurs via a spinodal decomposition at the very early stage. AM1 is a commercial single crystal Ni-based superalloy, which has been extensively used as the materials for high-pressure gas turbine blades and vanes in various aircraft engines.[1] It belongs to the first generation Re-free single crystal Ni-based superalloys. Its microstructure consists of cuboidal c¢ precipitates embedded into the c matrix after standard heat treatment. [1,2] It is subjected to a three-step heat treatment, i.e., solution, primary aging, and secondary aging heat treatments. The alloy is first solutionized at the single c field, and then cooled to precipitate a L1 2 -ordered c¢ phase from the face-centered cubic (fcc) c matrix. The cooling rate after solutionizing mainly determines the size, the morphology, and the distribution of c¢ precipitates. It is followed by the primary and secondary aging heat treatments at an intermediate temperature and a low temperature, which allows to refine the size and the morphology of c¢ precipitates. [3] The precipitation of c¢ phase has been widely studied in various Ni-based alloys, e.g., Ni-Al alloys, [4][5][6][7][8][9] Ni-AlCr alloys, [10][11][12] Ni-Al-Ti alloys, [13][14][15] polycrystalline superalloys, [16][17][18][19][20][21] etc. However, very few papers have been involved in the study of c¢ precipitation in single crystal Ni-based superalloys at early stage during the rapid cooling conditions. Since c¢ phase has a L1 2 ordered structure, c¢ phase separation must be accompanied by an ordering process. However, it still remains debatable with respect to the occurrence sequence of the spinodal clustering and atomic ordering. The chemical ordering would precede the spinodal decomposition due to the short-range atomic jump involved in the ordering process while long-range diffusion is needed for spinodal decomposition.

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“…The limitations associated with the resolution of experimental techniques have so far prevented direct atomic-scale imaging and interpretation of the structural and compositional transition across such interfaces. Techniques such as 3D Atom Probe (3DAP) Tomography have enabled detailed exploration of nanometer-scale elemental partitioning across interphase interfaces, including the = 0 interface in nickel base alloys [20][21][22][23][24][25][26]. In addition, developments in aberrationcorrected HRSTEM now permit Z contrast imaging (arising from the differences in atomic numbers) and interpretation at atomic resolution [27][28][29].…”

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Atomic Scale Structure and Chemical Composition across Order-Disorder Interfaces

et al. 2009

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Through a combination of aberration-corrected high-resolution scanning transmission electron microscopy and three-dimensional atom probe tomography, the true atomic-scale structure and change in chemical composition across the complex order-disorder interface in a metallic alloy has been determined. The study reveals the presence of two interfacial widths, one corresponding to an order-disorder transition, and the other to the compositional transition across the interface, raising fundamental questions regarding the definition of the interfacial width in such systems. DOI: 10.1103/PhysRevLett.102.086101 PACS numbers: 68.35.Àp, 68.37.Ma, 68.37.Vj Interfaces play an important role in determining several properties in multiphase systems [1][2][3]. Atomic-scale renditions of the interface structure have been primarily accomplished through high-resolution transmission electron microscope (HRTEM) phase-contrast images (and simulations) that allow for identification of the positions of atomic columns and structural defects at the interface [4,5]. Recent advances in HRTEM and HRSTEM have been enabled by the development of spherical aberration correctors for the electron probe as well as the image [6][7][8].In parallel, developments in first-principles based electronic structure calculations and larger scale atomistic modeling tools permit more accurate simulations of the interface structure [9,10]. Recent atomistic simulations of the interface between an ordered precipitate and disordered matrix in a nickel-base superalloy indicate that the interface is not abrupt at the atomic scale [9]. While the implications of these results on the microstructural stability [11][12][13] and high temperature mechanical properties [14][15][16][17][18][19] are substantial, there is no clear experimental evidence confirming these atomistic simulations. The limitations associated with the resolution of experimental techniques have so far prevented direct atomic-scale imaging and interpretation of the structural and compositional transition across such interfaces. Techniques such as 3D Atom Probe (3DAP) Tomography have enabled detailed exploration of nanometer-scale elemental partitioning across interphase interfaces, including the = 0 interface in nickel base alloys [20][21][22][23][24][25][26]. In addition, developments in aberrationcorrected HRSTEM now permit Z contrast imaging (arising from the differences in atomic numbers) and interpretation at atomic resolution [27][28][29]. Our study provides direct experimental evidence at the atomic scale of the true structure and composition of the = 0 interface in a nickel base alloy by coupling two advanced and complementary techniques: aberration-corrected HRSTEM and 3DAP.This work was carried out on the nickel base superalloy Rene' 88 DT [nominal composition 55.63Ni-18.02Cr-13.00Co-4.74Ti-4.45Al-2.48Mo-1.21W-0.46Nb (in at %)], with superior creep and fatigue properties for turbine disk applications [14][15][16]. The typical microstructure consists of a disordered fcc matrix with ordered ...

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Atom-probe microanalysis of a nickel-base superalloy

Cited by 51 publications

References 22 publications

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

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

Spinodal Decomposition Mechanism of γ′ Precipitation in a Single Crystal Ni-Based Superalloy

Atomic Scale Structure and Chemical Composition across Order-Disorder Interfaces

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