Understanding complex phase chemistry in a Ni-base superalloy: A combined AEM/APFIM approach

Alloy 718 is a Nb-modified Ni-base superalloy widely-used for gas turbine and related applications which require microstructural stability and good mechanical properties at elevated temperatures (≈ 650°C). In order to achieve the desired properties, the alloy is given a multi-step thermal treatment during which a complex multiphase microstructure is developed. The primary strengthening phases in this alloy are DO22-ordered γ" and Ll2-ordered γ'. A variety of other phases such as Laves, MC-type carbides, and δ (Ni3Nb) have been observed in this material. In this study, the techniques of analytical electron microscopy (AEM) and atom probe field-ion microscopy (APFIM) have been successfully applied to characterize the microstructure of Alloy 718.The nominal bulk composition of the material examined in this investigation is listed in Table 1 together with the heat treatment schedule. Specimens for AEM characterization were examined in a Philips EM400T analytical electron microscope operated at 120kV and equipped with a Link LZ5/AN10-85S analyzer system.

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SHaRE: Collaborative materials science research

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106089 ◽

1988 ◽

Vol 46 ◽

pp. 804-805

Author(s):

Edward A. Kenik ◽

Karren L. More

Keyword(s):

Electron Microscope ◽

Materials Science ◽

Analytical Electron Microscopy ◽

Science Research ◽

Atom Probe ◽

Probe Field ◽

Transmission Electron ◽

Wide Range ◽

Analytical Electron ◽

Electron Microscopes

The Shared Research Equipment (SHaRE) Program provides access to the wide range of advanced equipment and techniques available in the Metals and Ceramics Division of ORNL to researchers from universities, industry, and other national laboratories. All SHaRE projects are collaborative in nature and address materials science problems in areas of mutual interest to the internal and external collaborators. While all facilities in the Metals and Ceramics Division are available under SHaRE, there is a strong emphasis on analytical electron microscopy (AEM), based on state-of-the-art facilities, techniques, and recognized expertise in the Division. The microscopy facilities include four analytical electron microscopes (one 300 kV, one 200 kV, and two 120 kV instruments), a conventional transmission electron microscope with a low field polepiece for examination of ferromagnetic materials, a high voltage (1 MV) electron microscope with a number of in situ capabilities, and a variety of EM support facilities. An atom probe field-ion microscope provides microstructural and elemental characterization at atomic resolution.

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Origin and Influence of Pre-Existing Segregation on Radiation-Induced Segregation In Austenitic Stainless Steels

MRS Proceedings ◽

10.1557/proc-540-445 ◽

1998 ◽

Vol 540 ◽

Cited By ~ 6

Author(s):

E. A. Kenik ◽

J. T. Busby ◽

M. K. Miller ◽

A. M. Thuvander ◽

G. Was

Keyword(s):

Electron Microscopy ◽

Grain Boundaries ◽

Stainless Steels ◽

Analytical Electron Microscopy ◽

Austenitic Stainless Steels ◽

Atom Probe ◽

Molecular Ions ◽

Probe Field ◽

Analytical Electron ◽

Radiation Induced

AbstractThe pre-existing segregation at grain boundaries in two austenitic stainless steels has been investigated by atom probe field ion microscopy and analytical electron microscopy. In addition, the effect of radiation-induced segregation on the near-grain-boundary composition has been studied by analytical electron microscopy. Pre-existing enrichment of Cr, Mo, B, C and P and depletion of Fe and Ni near grain boundaries has been observed. Significant affinity between Mo and N in both alloys is indicated by the detection of MoN2+` molecular ions during field evaporation. The pre-existing segregation is modified by radiation-induced segregation resulting in Ni and Si enrichment near the boundary as well as depletion of chromium adjacent to the boundary resulting in a “W-shaped” Cr profile.

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Grain Boundary Intermetallic Phases in Alloy 718

MRS Proceedings ◽

10.1557/proc-186-215 ◽

1990 ◽

Vol 186 ◽

Cited By ~ 3

Author(s):

M. G. Burke ◽

M. K. Miller

Keyword(s):

Electron Microscopy ◽

Analytical Electron Microscopy ◽

Aging Treatment ◽

Intermetallic Phases ◽

Nickel Base Superalloy ◽

Alloy 718 ◽

Laves Phases ◽

Analytical Electron ◽

Nickel Base ◽

Base Superalloy

AbstractA nickel base superalloy, Alloy 718, has been studied by analytical electron microscopy in order to trace the development of the complex microstructure which is produced during a typical multistage thermal treatment. The distribution of δ γ″, γ′ and Laves phases was found to be strongly dependent on aging treatment.

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Identification Of G-Phase In Aged Cast CF 8 Type Stainless Steel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100118515 ◽

1985 ◽

Vol 43 ◽

pp. 328-329 ◽

Cited By ~ 3

Author(s):

J. Bentley ◽

M. K. Miller ◽

S. S. Brenner ◽

J. A. Spitznagel

Keyword(s):

Stainless Steel ◽

Nuclear Reactors ◽

Analytical Electron Microscopy ◽

Atom Probe ◽

Duplex Structure ◽

Primary Coolant ◽

Probe Field ◽

Aged Material ◽

Type Stainless Steel ◽

Analytical Electron

The microstructure of as-cast and aged CF 8 type stainless steel, used for the primary coolant pipes in pressurized light-water nuclear reactors, is being studied by analytical electron microscopy (AEM) and atom probe field-ion microscopy (APFIM). The phase transformations of the ferrite (∼19 vol % of the duplex structure) that occur after aging at 673 K for 7500 h are described by Miller et al. The present work deals with the identification of G-phase (prototype compound Ni16Ti6Si7) observed in the ferrite of aged material.In FIM images the precipitates had bright contrast, appeared roughly spherical, were ∼10 nm in diameter, and were present at a concentration of ∼1023 m-3. Atom probe selected area microchemical analyses of the central portion of five precipitates revealed that they were alloy silicides, Table 1.

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Combined Atom-Probe and Electron Microscopy Characterization of Fine Scale Structures in Aged Primary Coolant Pipe Stainless Steel

MRS Proceedings ◽

10.1557/proc-82-163 ◽

1986 ◽

Vol 82 ◽

Cited By ~ 3

Author(s):

J. Bentley ◽

M. K. Miller

Keyword(s):

Electron Microscopy ◽

Analytical Electron Microscopy ◽

Atom Probe ◽

Primary Coolant ◽

Probe Field ◽

Α Phase ◽

Complementary Nature ◽

Microscopy Characterization

ABSTRACTThe capabilities and complementary nature of atom probe field-ion microscopy (APFIM) and analytical electron microscopy (AEM) for the characterization of finescale microstructures are illustrated by examination of the changes that occur after long term thermal aging of cast CF 8 and CF 8M duplex stainless steels. In material aged at 300 or 400°C for up to 70,000 h, the ferrite had spinodally decomposed into a modulated fine-scaled interconnected network consisting of an iron-rich α′ phase and a chromium-enriched α phase with periodicities of between 2 and 9 nm. G-phase precipitates 2 to 10 nm in diameter were also observed in the ferrite at concentrations of more than 1021 m−3. The reported degradation in mechanical properties is most likely a consequence of the spinodal decomposition in the ferrite.

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Atom Probe Tomography Of Interfaces

Microscopy and Microanalysis ◽

10.1017/s143192760001391x ◽

1999 ◽

Vol 5 (S2) ◽

pp. 118-119

Author(s):

M. K. Miller

Keyword(s):

Atom Probe Tomography ◽

Small Volume ◽

Atom Probe ◽

Solute Segregation ◽

Alloy 718 ◽

Polycrystalline Nickel ◽

Concentration Gradients ◽

Precipitate Morphology ◽

Probe Field ◽

Nickel Based Superalloy

The technique of atom probe tomography (APT) enables the x, y, and z coordinates and the elemental identities of the atoms in a small volume to be determined at the atomic level. Therefore, the APT technique may be used to characterize solute segregation to interfaces and precipitation in terms of concentration gradients and precipitate morphology. This type of information may be used to optimize the design of alloys.The material that was used to illustrate the capabilities of atom probe tomography is a complex polycrystalline nickel-based superalloy, Alloy 718. The composition of this commercial superalloy is Ni- 3.2 at. % Nb, 0.96% Al, 1.15% Ti, 20.3% Fe, 21.8% Cr, 0.26% Co, 1.8% Mo, 0.16% Mn, 0.21% Si and 0.26% C. The material was characterized after a heat treatment oM h at 1038°C + 8 h at 870°C + 500 h at 600°C. Previous atom probe field ion microscopy characterizations of this material has demonstrated that there is no intragranular precipitation after the anneal at 1038°C.

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A combined TEM/APFIM approach to the study of phase transformations: Phase identification in the Fe-Be system

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105965 ◽

1988 ◽

Vol 46 ◽

pp. 780-781

Author(s):

M.G. Burke ◽

M.K. Miller

Keyword(s):

Phase Transformations ◽

Microstructural Analysis ◽

Analytical Electron Microscopy ◽

Thin Foil ◽

Atom Probe ◽

Microstructural Development ◽

Phase Identification ◽

Probe Field ◽

Isothermal Ageing ◽

Microscopy Techniques

Phase transformation investigations rely on the identification and characterization of the microstructure in order to understand the formation, development, and relative stability of the constituent phases. Although transmission and associated analytical electron microscopy techniques have made substantial contributions by providing structural and chemical data necessary for the detailed microstructural analysis, the direct atomic structure and chemistry are not readily discernable. By combining TEM techniques with atom probe field-ion microscopy (APFIM), it is possible to obtain a complete structural and chemical analysis of the constituent phases. In this paper, the microstructural development which occurs during ageing in an Fe-25 at. % Be alloy is presented to illustrate the complementary nature of the techniques and demonstrate the applicability of the combined TEM/APFIM approach in the study of phase transformations.An Fe-25 at. % Be alloy was solution annealed at 1100°C for 0.5 h and water-quenched prior to isothermal ageing at 650°C for 4 h. Thin foil specimens were examined in a Philips EM430T operated at 300 kV and in a JEOL 200CX operated at 200 kV. FIM needle specimens were electropolished and analyzed in the ORNL energy-compensated APFIM.

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Applications of atom-probe field-ion microscopy to the study of interfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100150149 ◽

1993 ◽

Vol 51 ◽

pp. 862-863

Author(s):

M.G. Burke ◽

M.K. Miller

Keyword(s):

Analytical Electron Microscopy ◽

Atom Probe ◽

Pressure Vessels ◽

Low Alloy Steels ◽

Probe Field ◽

Microchemical Analysis ◽

Elemental Sensitivity ◽

Alloy Steels ◽

Field Ion Microscope ◽

Microstructural Studies

The near-atomic resolution and elemental sensitivity of the atom probe field-ion microscope (APFIM) permit the detailed microstructural and microchemical analysis of phases and interfaces in a variety of materials. To overcome the limitation of this technique in terms of volume of material sampled, it is frequently necessary to perform complementary microstructural studies by other techniques such as analytical electron microscopy (AEM) or auger electron spectroscopy (AES). With such complementary data, the microstructural significance of the APFIM data can be exploited. In addition to specifically evaluating segregation at interfaces, the high spatial resolution of the APFIM technique can be used to determine microcompositional fluctuations in the vicinity of interfaces. In this overview, some selected examples illustrating the application of the APFIM technique to the evaluation of segregation to interfaces are presented.Considerable research has been performed on low alloy steels, particularly those such as A533B which are used in the pressure vessels of nuclear reactors.

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Steady State Phase Diagram of Cu-Ag Under Ball Milling: An XRD and APFIM Study

MRS Proceedings ◽

10.1557/proc-581-271 ◽

1999 ◽

Vol 581 ◽

Author(s):

F. Wu ◽

P. Bellon ◽

A.J. Melmed ◽

T.A. Lusby

Keyword(s):

Phase Diagram ◽

Steady State ◽

Ball Milling ◽

Elevated Temperatures ◽

Atom Probe ◽

X Ray Diffraction ◽

Probe Field ◽

Three Phase ◽

Milling Temperature

ABSTRACTThe nature of the steady state reached during ball milling of CuxAg1−x powders (x=35 to 75) is studied as a function of the milling temperature (85K≤T≤503K). The characterization of the powders is performed by using x-ray diffraction, differential calorimetry and atom probe field ion microscopy. A steady-state phase diagram is built. Three-phase coexistence is shown to generally take place at intermediate milling temperatures. Atom probe data reveals that the solid solution stabilized by low milling temperature is nearly random, where as milling at elevated temperatures results in the decomposition of the elements at a lengthscale of 20∼30 nm.

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