Welding Metallurgy of

Review of supercritical CO2 power cycles integrated with CSP

Transition of creep damage region in dissimilar welds between Inconel 740H Ni-based superalloy and P92 ferritic/martensitic steel

Hot deformation characteristics and processing map analysis of a new designed nickel-based alloy for 700 °C A-USC power plant

The hot deformation behavior of a new-designed nickel-based alloy with different initial states were investigated by isothermal compression at temperature range of 1000–1200 °C with strain rate of 0.01–20 s −1 and nominal strain of 15–70% on a Gleeble-1500 thermo-mechanical simulator. The correlation of dynamic recrystallization (DRX) mechanism and initial alloy states as well as deformation parameters were analyzed in detail by means of transmission electron microscope (TEM) and electron backscattered diffraction (EBSD). For homogenized alloy with extremely large grains, the DRX mechanism transforms partly from discontinuous dynamic recrystallization (DDRX) characterized with serrated and bulging grain boundary into continuous dynamic recrystallization (CDRX) operated by progressive sub-grain merging and rotation with the increasing strain rate and decreasing deformation temperature, which results from the poor deformation compatibility in the alloy with extremely large grains. However, the dominant DRX mechanism in as-forged alloy is DDRX almost at all the deformation conditions, and CDRX is only an assistant mechanism, which caused by the initial inhomogeneous dislocation distribution and fine grains. In consequence, the initial alloy states have a significant influence on the DRX, which cannot be ignored in the hot deformation research.

Dynamic recrystallization of a new nickel-based alloy for 700 °C A-USC power plant applications with different initial states: as-homogenized and as-forged

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

Microstructure Stability of Alloy 740H and its Effect on Material Properties

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Properties of INCONEL Alloy 740H for High Pressure Steam and Supercritical CO2 Applications

The development of Generation 3 (Gen 3) concentrated solar power (CSP) plants is progressing with the goal of reduced overall costs through a combination of innovative design and improved cycle efficiency. The envisaged systems couple a high efficiency power block using supercritical CO2 (sCO2) as a working fluid with temperatures >715°C and either novel salts, solids, or gas for the new receivers and heat-transfer media. Nickel-based structural alloys, already used in limited quantities in today’s molten salt CSP receivers, will be required in higher quantities for multiple power plant components due to the significant increases in fluid/media temperatures compared to today’s plants. In this work, a preliminary study has been completed to assess the feasibility of using welded tube manufacturing to produce INCONEL® Alloy 740H® thin-wall tubes, which are a key component in most solar receiver designs. Alloy 740H® is an age- hardenable nickel-based alloy with significantly greater high-temperature strength up to ∼800°C compared to traditional solid solution alloys such as alloy UNS N06230. Due to its higher utilization of material, lower wear on processing equipment, and reduced intermediary steps, welded tube manufacturing offers significant cost reduction potential (up to 30%) compared to seamless tube produced via several draw plus anneal operations. The results presented herein show that successful production of Alloy 740H® is possible with properties that can meet the basic materials standards. Based on these successful results, the need and outline of a more extensive evaluation plan is provided to ultimately allow the use of this material through the more stringent requirements of boiler and pressure vessel codes which will be used to construct future Gen 3 systems.

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Materials improvements for improved economy of high-temperature components in future gen 3 CSP systems

Characterization of γ′ coarsened zones (CZs) in alloy 740H fusion welds via a variety of electron microscopy techniques was conducted. The effects of solute partitioning during nonequilibrium solidification on the amount of strengthening precipitates along the grain boundaries were evaluated via electron-probe microanalysis and scanning electron microscopy. Electron backscatter diffraction was used to present evidence for the preferential growth of CZs toward regions of lower γ′ content, even if growth in that direction increases grain boundary area. Scanning electron microscopy and image analysis were used to quantify the propensity for CZs to develop along certain segments of the grain boundaries, as governed by the local variations in γ′ content. Scanning transmission electron microscopy with X-ray energy-dispersive spectrometry (XEDS) was used to assess the compositions of the matrix and precipitate phases within the CZs and to quantify the segregation of alloying components to the reaction front. Thermodynamic and kinetic modeling were used to compare calculated and experimental compositions. The work presented here provides new insight into the progression of the discontinuous coarsening (DC) reaction in a complex engineering alloy.

John J. de Barbadillo

Papers

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

Microstructure Stability of Alloy 740H and its Effect on Material Properties

Properties of INCONEL Alloy 740H for High Pressure Steam and Supercritical CO2 Applications

Materials improvements for improved economy of high-temperature components in future gen 3 CSP systems

Characterization of Discontinuous Coarsening Reaction Products in INCONEL® Alloy 740H® Fusion Welds