Aging precipitation behavior and mechanical properties of Inconel 617 superalloy aged at 760 °C for up to 10000 h were investigated. The results showed that the precipitates of the aged alloy are M
 23C6 and M
 6C carbides and γ′ phase. The carbide particles precipitated both at the grain boundaries and within grains, and the γ′ phase particles were situated at intragranular sites in the process of aging. The carbide particles were discontinuously dispersed at grain boundaries after aging for 3000 h, while after aged for 5000 h the carbide particles are merged. The precipitates inside grains remained stable even after aging for 10000 h. The hardness was increased for the alloy aged for 300 h up to 3000 h, which was resulted primarily from the precipitation of carbides as discrete particles both at the grain boundaries and inside grains. Small quantity γ′ precipitates were formed inside grains, to some extent, which contributed to an enhanced hardness. However, a decrease of the hardness was observed after aging for 5000 h. A significant drop in toughness of the alloy aged for 300 h was attributed to the reduction of the bonding interface strength when carbides precipitated at grain boundaries. Thereafter, the toughness decreased slowly with the prolonged aging time. The high temperature tensile properties of the aged alloy are rather stable even aged for 300–3000 h.

Aging precipitation behavior and mechanical properties of Inconel 617 superalloy

Electron microscopy techniques have been used to investigate the cause of premature creep failure in the fusion zone of INCONEL® Alloy 740H® (INCONEL and 740H are registered trademarks of Special Metals Corporation) welds. The reduced creep rupture lives of all-weld-metal and cross-weld creep specimens (relative to base metal specimens) have been attributed to the presence of large grain boundary regions that were denuded in fine γ′ but contained coarse, elongated particles. Investigation of creep rupture specimens has revealed four factors that influence the formation of these coarsened zones, and the large particles found within them have been identified as γ′. Comparisons of the microstructural characteristics of these zones to the characteristics that are typical of denuded zones formed by a variety of mechanisms identified in the literature have been made. It is concluded that the mechanism of γ′-denuded zone formation in alloy 740H is discontinuous coarsening of the γ′ phase. The discontinuous reaction is catalyzed by the grain boundary migration and sliding which occur during creep and likely promoted by the inhomogeneous weld metal microstructure that results from solute segregation during solidification. The increased susceptibility to the formation of the observed γ′-denuded zones in the weld metal as compared to the base metal is discussed in the context of differences in the contributions to the driving force for the discontinuous coarsening reaction.

Microstructural Evolution of INCONEL® Alloy 740H® Fusion Welds During Creep

Abstract The corrosion behavior of nickel (Ni)-based alloys used for low-temperature aqueous or condensed systems is reviewed in detail in this paper. Commercially available pure Ni, nickel-copper (Ni-Cu), nickel-molybdenum (Ni-Mo), nickel-chromium-molybdenum (Ni-Cr-Mo), and nickel-chromium-iron (Ni-Cr-Fe) alloys as well as cast Ni-based alloys are addressed. It is shown that Ni-Cr-Mo alloys are multipurpose alloys that can be used in both reducing and oxidizing conditions. Special attention is given to a few Ni alloys, which not only extend the range of usefulness of existing alloys by overcoming their limitations but are also reliable and cost-effective and have opened new areas of applications.

On the performance of commercially available corrosion-resistant nickel alloys: a review

Future advanced nuclear plants are considered to operate as cogeneration plants for electricity and heat. Metals and alloys will be the main portion of structural materials employed (including fuel claddings). Due to the operating conditions these materials are exposed to damaging conditions like creep, fatigue, irradiation and its combinations. The paper uses the most important alloys: ferritic-martensitic steels, superalloys, oxide dispersion strengthened steels and to some extent titanium aluminides to discuss its responses to these exposure conditions. Extrapolation of stress rupture data, creep strain, swelling, irradiation creep and creep–fatigue interactions are considered. Although the stress rupture- and the creep behavior seem to meet expectations, the long design lives of 60 years are really challenging for extrapolations and particularly questions like negligible creep or occurrence of diffusion creep need special attention. Ferritic matrices (including oxide dispersion strengthened (ODS), steels) have better irradiation swelling behavior than austenites. Presence and size of dispersoids having a strong influence on high-temperature strength bring only insignificant improvements in irradiation creep. A strain-range-separation based approach for creep–fatigue interactions is presented which allows a real prediction of creep–fatigue lives. An assessment of capabilities and limitations of advanced materials modeling tools with respect to damage development is given.

/pdf/damage-assessment-in-structural-metallic-materials-for-1oebiqh4jp.pdf

Damage assessment in structural metallic materials for advanced nuclear plants

Thermodynamic and kinetic modeling were used to determine appropriate heat treatment schedules for homogenization and second phase dissolution in INCONEL® alloy 740H® (INCONEL and 740H are registered trademarks of Special Metals Corporation) fusion welds. Following these simulations, a two-step heat treatment process was applied to specimens from a single pass gas tungsten arc weld (GTAW). Scanning electron microscopy (SEM) has been used to assess the changes in the distribution of alloying elements as well as changes in the fraction of second phase particles within the fusion zone. Experimental results demonstrate that adequate homogenization of alloy 740H weld metal can be achieved by a 1373 K/4 h (1100 °C/4 h) treatment. Complete dissolution of second phase particles could not be completely achieved, even at exposure to temperatures near the alloy’s solidus temperature. These results are in good agreement with thermodynamic and kinetic predictions.

Homogenization and Dissolution Kinetics of Fusion Welds in INCONEL® Alloy 740H®

A novel nickel-based superalloy INCONEL 740 was under development for application in ultra-supercritical superheater tubers above 750°C. The precipitation behaviors of η phase and γ′ particles of the alloy were investigated through experimental study and phase computation. Experimental results showed that η phase formed a Widmanstatten pattern structure following long-term exposure at elevated temperatures and that the coarsening of γ′ particle follows a cube rate law: r−3 ∝ t. Thermodynamic calculation results showed that Al and Ti had an important effect on the precipitation behavior of γ′ and η phases. Two suggested novel modified alloys, wherein the Al and Ti contents were modified, were designed and melted for the experimental study. The preliminary results indicated that the modified alloys exhibited higher structural stability following long-term exposure at 750°C till 5000h.

Experimental investigation and thermodynamic calculation on phase precipitation of inconel 740

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Experimental investigation and thermodynamic calculation on phase precipitation of inconel 740