The Advanced Materials and Manufacturing Technologies (AMMT) program is aiming at the accelerated incorporation of new materials and manufacturing technologies into nuclear-related systems. Complex Ni-based components fabricated by laser powder bed fusion (LPBF) could enable operating temperatures at T > 700°C in aggressive environments such as molten salts or liquid metals. However, available mechanical properties data relevant to material qualification remains limited, in particular for Ni-based alloys routinely fabricated by LPBF such as IN718 (Ni- 19Cr-18Fe-5Nb-3Mo) and Haynes 282 (Ni-20Cr-10Co-8.5Mo-2.1Ti-1.5Al). Creep testing was conducted on LPBF 718 at 600°C and 650°C and on LPBF 282 at 750°C. finding that the creep strength of the two alloys was close to that of wrought counterparts. with lower ductility at rupture. Heat treatments were tailored to the LPBF-specific microstructure to achieve grain recrystallization and form strengthening γ' precipitates for LPBF 282 and γ' and γ" precipitates for LPBF 718. In-situ data generated during printing and ex-situ X-ray computed tomography (XCT) scans were used to correlate the creep properties of LPBF 282 to the material flaw distribution. In- situ data revealed that spatter particles are the potential causes for flaws formation in LPBF 282. with significant variation between rods based on their location on the build plate. XCT scans revealed the formation of a larger number of creep flaws after testing in the specimens with a higher initial flaw density. which led to a lower ductility for the specimen.

This study investigates the steam oxidation behavior of Alloy 699 XA, a material containing 30 wt.% chromium and 2 wt.% aluminum that forms protective oxide scales in low-oxygen conditions. The research compares four variants of the alloy: conventional bulk material, a laser powder bed fusion (LPBF) additively manufactured version, and two modified compositions. The modified versions include MAC-UN-699-G, optimized for gamma-prime precipitation, and MAC-ISIN-699, which underwent in-situ internal nitridation during powder atomization. All variants were subjected to steam oxidation testing at 750°C and 950°C for up to 5000 hours, with interim analyses conducted at 2000 hours. The post-exposure analysis employed X-ray diffraction (XRD) to identify phase development and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) to examine surface morphology, cross-sectional microstructure, and chemical composition. This study addresses a significant knowledge gap regarding the steam oxidation behavior of 699 XA alloy, particularly in its additively manufactured state.

During the last decades, new generations of Ni-based superalloys have emerged with judiciously controlled chemistries. These alloys heavily rely on the addition of refractory elements to enhance their mechanical properties at elevated temperatures; however, a clear interpretation of the influence of these minor-element additions on the alloy's high-temperature oxidation behavior is still not well understood, particularly from the standpoint of predicting the transition from internal to external alumina formation. In this context, the present investigation describes a systematic study that addresses the intrinsic effects that minor element additions of Nb, Ta, and Re have on the oxidation behavior of alumina-scale forming γ-Ni alloys. By combining a novel simulation approach with high-temperature oxidation experiments, the present study evidences the generally positive effect associated with 2 at. % addition of Ta and Re as well as the detrimental consequences of Nb additions on the 1100 °C oxidation of (in at. %) Ni-6Al-(0,4,6,8)Cr alloys.

To improve the economics of critical components, such as receivers and heat exchangers, for Generation 3 (Gen 3) concentrating solar power (CSP) plants, research was conducted to understand how manufacturing impacts the high-temperature performance of various tube production routes. Gen 3 CSP components are expected to require the use of heat-resistant nickel- based alloys due to the elevated operating temperatures in designs carrying molten salt or supercritical CO 2 . INCONEL alloy 740H (alloy 740H) was investigated as an alternative to UNS N06230 (alloy 230) as it possesses superior high-temperature creep strength which can lead to overall reductions in material cost. A key challenge is understanding how autogenous seam welding with and without re-drawing can be used to manufacture thin-wall tubing for CSP receivers and heat-exchangers to further reduce costs over traditional seamless production routes. Alloy 740H welded tube was successfully fabricated and re-drawn to several relevant tube sizes. Since traditional mechanical testing samples could not be removed from the thin-wall tubing, full-sized tubes were used for tensile, fatigue, and vessel testing (internally pressurized creep- rupture) which was critical to understanding the weld performance of the manufactured product forms. The generated vessel test data exhibited a creep strength reduction when compared to wrought product with no clear trend with temperature or test duration. It was found that redrawing the welded tubes improved the creep strength to approximately 82% of the wrought material performance and elevated temperature tensile and fatigue behavior exceeded 85% of the design minimums. Detailed, post-test characterization found that nano-sized carbides formed during the laser seam-welding process remained stable after multiple solution-annealing steps, which restricted grain growth, and impacted the time-dependent performance. This paper will focus on the time-dependent behavior of the examined welded and redrawn tubes, supporting metallographic evidence, and give perspective on future considerations for using alloy 740H in CSP components.

A United States-based consortium has successfully completed the Advanced Ultra-Supercritical Component Test (A-USC ComTest) project, building upon a 15-year materials development effort for coal-fired power plants operating at steam temperatures up to 760°C. The $27 million project, primarily funded by the U.S. Department of Energy and Ohio Coal Development Office between 2015 and 2023, focused on validating the manufacture of commercial-scale components for an 800 megawatt power plant operating at 760°C and 238 bar steam conditions. The project scope encompassed fabrication of full-scale components including superheater/reheater assemblies, furnace membrane walls, steam turbine components, and high-temperature transfer piping, utilizing nickel-based alloys such as Inconel 740H and Haynes 282 for high-temperature sections. Additionally, the team conducted testing to secure ASME Code Stamp approval for nickel-based alloy pressure relief valves. This comprehensive effort successfully established technical readiness for commercial-scale A-USC demonstration plants while developing a U.S.-based supply chain and providing more accurate cost estimates for future installations.

The voestalpine foundry group, operating at locations in Linz and Traisen, Austria, specializes in heavy steel casting components ranging from 1 to 200 tons for power generation, oil and gas, chemical processing, and offshore applications. Their manufacturing expertise encompasses high-alloyed martensitic 9-12% Cr-steels and nickel-based Alloy 625, particularly for ultra-supercritical (USC) and advanced USC power generation systems operating at temperatures from 600°C to over 700°C. The production of these complex, thick-walled components relies on advanced thermodynamic calculation and simulation for all thermal processes, from material development through final casting. The foundries’ comprehensive capabilities include specialized melting, molding, heat treatment, non-destructive testing, and fabrication welding, with particular emphasis on joining dissimilar cast, forged, and rolled materials. Looking toward future innovations, the group is exploring additive manufacturing for mold production and robotic welding systems to enhance shaping and surface finishing capabilities.

Nuclear reactor inspections occasionally identify degraded materials in irradiated reactor components. Although mechanical repair options are possible, these repair solutions may be cost prohibitive or impractical to implement due to access restraints and/or the severity of the degradation. Welding repair of reactor components may input excessive heat into these irradiated materials resulting in diffusion of trace amounts of helium within the grain boundaries of the weld heat-affected zone (HAZ). Intergranular HAZ cracking can then result from the combination of this helium diffusion and high localized tensile stresses generated during weld cooling. It is therefore critical to characterize these zones and understand limitations for welding highly irradiated components to prevent helium-induced cracking. To accomplish this, typical reactor structural materials including Types 304L and 316L stainless steels and nickel-based Alloy 600/182 materials irradiated within the High Flux Isotope Reactor facility at Oak Ridge National Laboratory were used in this study for welding and evaluation. A phased array ultrasonic inspection system has been developed to characterize cracking in the weld samples. It provides remote controlled scanning and minimizes handling the samples, minimizing operator dose. The samples are inspected from the side opposite of the welds. The material and weld grain noise were evaluated at 10 MHz and found to be conducive to detecting cracking in the material and welds. Inspection of the samples comprises a 10 MHz phased array probe sweeping a focused longitudinal wave from -60° to 60° while the probe is raster scanned over the sample in small increments. The collected data is analyzed using UltraVision 3. Several of the irradiated samples were inspected prior to welding. Some of the samples had what appear to be small lamination defects in them. One irradiated welded sample has been tested to date with no cracking detected, which has been confirmed by destructive examination.

This paper reports on the latest in a series of projects aiming at the qualification of new and proven materials in components under a severe service environment. In the initial stages of the project (HWT I & HWT II), a test loop at Unit 6 of the GKM Power Plant in Mannheim was used to study the behavior of components for advanced ultra-supercritical (A-USC) plants made from nickel alloys at 725 °C under both static and fluctuating conditions. Due to recent changes in the operation modes of existing coal-fired power plants, the test loop was modified to continue operating the existing nickel components in the static section while applying thermal cycles in a different temperature range. HR6W pipes and valves were added to the bypass of the static section, and all components in the cyclic section were replaced with P92, P93, and HR6W components. The test loop achieved approximately 9000 hours of operation and around 800 cycles with holding times of 4 and 6 hours. After dismantling the loop, nondestructive and destructive examinations of selected components were conducted. The accompanying testing program includes results from thermal fatigue, fatigue, thermal shock, and long-term creep tests, focusing on the behavior of base materials and welds, particularly for HR6W, P92, P93, and other nickel-based alloys. Additionally, test results on dissimilar welds between martensitic steel P92 and nickel alloys A617 and HR6W are presented. Numerical assessments using standardized and numerical lifetime estimation methods complement the investigations. This paper provides insights into the test loop design and operational challenges, material behavior, and lifetime, including advanced numerical simulations and operational experiences with valves, armatures, piping, and welds.

Additive manufacturing is a groundbreaking manufacturing method that enables nearly lossless processing of high-value materials and produces complex components with a level of flexibility that traditional methods cannot achieve. Wire arc additive manufacturing (WAAM), utilizing a conventional welding process such as gas metal arc welding, is one of the most efficient additive manufacturing technologies. The WAAM process is fully automated and guided by CAD/CAM systems on robotic or CNC welding platforms. This paper explores the fundamental concepts and metallurgical characteristics of WAAM. It focuses primarily on the mechanical properties of printed sample structures made from P91, X20, and alloys 625 and 718 wire feedstock. The study particularly addresses the anisotropy of mechanical properties through both short-term and long-term testing, comparing these results to materials processed using conventional methods.

In this paper, the dissimilar metal welds (DMWs) between 617B nickel-based alloy and 10%Cr martensitic heat-resistant steel filled by 617 filler metal was studied, focused on the high temperature creep rupture properties. The high temperature creep rupture properties of welded joints with different welding processes were tested, and the microstructure of welded joints before and after the creep rupture test was observed by OM and SEM. The results showed that, there were three failure modes: base metal failure, type W failure and interface failure, among which interface failure caused the most serious life reduction. The welded joints using ER NiCr-3 filler metal reduced the strain concentration at the interface, so the fracture location shifted from the interface to HAZ of 10%Cr martensitic heat-resistant steel under high temperature and low stress conditions, and creep rupture life was improved. Similarly, weld cap shifted the creep crack propagation path by changing the groove form, so as to altered the stress state of joint and prolong the creep rupture life.

This presentation compares the corrosion resistance of uncoated Haynes 230 and SS316HS substrates to the same substrates coated with a Fe-based amorphous alloy. The substrates were exposed to highly corrosive media, FLiNaK, for 120 hours at 700 °C. The findings indicate that the thermal spray amorphous alloy coating provided superior corrosion resistance within the coatings while protecting the substrates against the aggressive environment. As a result, the new amorphous metal coating improved the substrate's lifespan by providing better protection against high-temperature corrosion, paving the way for a more efficient and cost-effective future in various industrial applications.

Hydrogen as a clean fuel is increasingly being used to propel gas turbines and to power combustion engines. Metallic materials including Ni-based alloys are commonly used in conventional gas turbines and combustion engines. However, hydrogen may cause embrittlement in these materials, depending on their chemical composition. In this work, the hydrogen embrittlement behavior of Ni-based alloys containing up to 50 wt.% Fe has been investigated using slow strain rate tensile testing, under cathodic hydrogen charging at room temperature. It was found that the larger the Ni equivalent concentration in an alloy, the more severe the hydrogen embrittlement. It was also found that solid solution alloys have less severe hydrogen embrittlement than precipitation alloys of the same Ni equivalent concentration. In solid solution alloys, hydrogen embrittlement led to cleavage type fracture, which is in line with literature where hydrogen enhanced planar deformation. In precipitation alloys, hydrogen embrittlement resulted in a typical intergranular fracture mode.

Coke drums experience failures in through-wall cracking throughout their operating life, resulting from low cycle fatigue. Coke drums are typically fabricated from Chrome Moly (CrMo) steels. This study was performed on P4 (1.25Cr-0.5Mo) base material using ER70S-B2L and Alloy 625 (ERNiCrMo-3) filler materials. Specimens were welded with the temper-bead/controlled deposition welding technique. The weld processes used were HP-GTAW, GMAW and SMAW. The fatigue performance, HAZ hardness and toughness of the weld samples was evaluated. The HP-GTAW welds exhibited an order of magnitude improvement in fatigue performance when compared to the other weld processes using ER70S-B2L filler material. The HP-GTAW welds also exhibited improved HAZ hardness and toughness when compared to the other weld processes. This presentation will introduce the HP-GTAW process, its features, and benefits and where it is applied in Coke drum repair welding. Comparative test results of the different weld processes for fatigue performance, HAZ tempering, and toughness will also be presented.

Supercritical CO 2 (sCO 2 ) is of interest as a working fluid for several concepts including the direct- fired Allam cycle as a low-emission fossil energy power cycle. Over the past 10 years, laboratory exposures at 300 bar sCO 2 have found reasonably good compatibility for Ni-based alloys at <800°C, including an assessment of the sCO 2 impact on room temperature mechanical properties after 750°C exposures. However, initial screening tests at 1 and 20 bar CO 2 at 900°-1100°C showed poor compatibility for Ni-based alloys. In an open cycle, the introduction of 1%O 2 and 0.1- 0.25%H 2 O impurities at 300 bar increased the reaction rates ≥2X at 750°C. At lower temperatures, steels are susceptible to C ingress and embrittlement. Creep-strength enhanced ferritic steels may be limited to <550°C and conventional stainless steels to <600°C. Two strategies to increase those temperatures are higher Ni and Cr alloying additions and Al- or Cr-rich coatings. Alloy 709 (Fe- 20Cr-25Ni) shows some promising results at 650°C in sCO 2 but reaction rates were accelerated with the addition of O 2 and H 2 O impurities. Pack aluminized and chromized Gr.91 (Fe-9Cr-1Mo) and type 316H stainless steel show some promise at 600°-650°C but further coating optimization is needed.

There is a critical lack of data on the mechanical behavior of candidate structural materials for advanced nuclear reactors under molten halide salt environments. Limited legacy data from the molten salt reactor experiment (MSRE) program showed a significant reduction in creep rupture strength of a Ni-base alloy in molten fluoride salt. With ongoing efforts to commercialize different molten salt reactor concepts, the industry can considerably benefit from quantitative information on the impact of molten halide salts on the engineering properties such as creep and fatigue strength of materials of interest. The present work aims to assess the role of molten salt corrosion on the creep behavior of three alloys 316H, 617 and 282 at 650-816 °C. Creep tests were conducted in fluoride (FLiNaK) and chloride (NaCl-MgCl 2 ) salts. Initial results from the ongoing testing will be presented which suggest that the molten salt environment caused a 25-50% reduction in creep rupture lifetime compared to air exposures. Physics-based corrosion and creep models were employed to gain some insights into the potential degradation mechanisms.

Solidification cracking (SC) is a defect that occurs in the weld metal at the end of the solidification. It is associated with the presence of mechanical and thermal stresses, besides a susceptible chemical composition. Materials with a high solidification temperature range (STR) are more prone to the occurrence of these defects due to the formation of eutectic liquids wetting along the grain boundaries. The liquid film collapses once the structure shrinks and stresses act during the solidification. Thus, predicting the occurrence of SC before the welding process is important to address the problem and avoid the failure of welded components. The nuclear power industry has several applications with dissimilar welding and SC-susceptible materials, such as austenitic stainless steels, and Ni-based alloys. Compositional optimization stands out as a viable approach to effectively mitigate SC in austenitic alloys. The integration of computational modeling into welding has significantly revolutionized the field of materials science, enabling the rapid and cost-effective development of innovative alloys. In this work, a SC resistance evaluation is used to sort welding materials based on a computational fluid dynamic (CFC) model and the alloy's chemical composition. An index named Flow Resistance Index (FRI) is used to compare different base materials and filler metals as a function of dilution. This calculation provides insights into the susceptibility to SC in dissimilar welding, particularly within a defined dilution range for various alloys. To assess the effectiveness of this approach, the relative susceptibility of the materials was compared to well-established experimental data carried out using weldability tests (Transvarestraint and cast pin tear test). The FRI calculation was programmed in Python language and was able to rank different materials and indicate the most susceptible alloy combination based on the dilution and chemical composition.

Ductility dip cracking (DDC) is known to occur in highly restrained welds and structural overlays made using high chromium (Cr) nickel (Ni) based filler metals in the nuclear power generation industry, resulting in costly repairs and reworks. Previous work explored the role of mechanical energy imposed by the thermo-mechanical cycle of multipass welding on DDC formation in a highly restrained Alloy 52 filler metal weld. It was hypothesized that imposed mechanical energy (IME) in the recrystallization temperature range would induce dynamic recrystallization (DRX), which is known to mitigate DDC formation. It was not shown however that IME in the recrystallization temperature range (IMERT) induced DRX. The objective of the work is to discern if a relationship between IMERT and DRX exists and quantify the amount of DRX observed in a filler metal 52 (FM-52) groove weld. DRX was analyzed and quantified using electron beam scattered diffraction (EBSD) generated inverse poll figures (IPF), grain surface area and grain aspect ratio distribution, grain orientation spread (GOS), kernel average misorientation (KAM), and grain boundary (GB) length density. From the analysis, GOS was determined to be an unsuitable criterion for quantifying DRX in multipass Ni-Cr fusion welds. Based on the observed criteria, higher IMERT regions correlate to smaller grain surface area, larger grain boundary density, and higher grain aspect ratio, which are all symptoms of DRX. High IMERT has a strong correlation with the symptoms DRX, but due to the lack of observable DRX, creating a threshold for DRX grain size, grain aspect ratio, and GB density is not possible. Future work will aim to optimize characterization criteria based on a Ni-Cr weld with large presence of DRX.

Nitridation is a high-temperature material degradation issue that can occur in air and in environments containing nitrogen, ammonia, etc., and in a variety of industrial processes. The nitridation behavior of several commercial nickel- and cobalt-based alloys is reviewed in this paper. The alloys include Haynes 230, Haynes 188, Haynes 625, Haynes 617, Haynes 214, Hastelloy X, and Haynes 233. The environments discussed are high-purity nitrogen gas between 871°C and 1250°C, 100% ammonia gas at 982°C and 1092°C, and a simulated combustion atmosphere at 982°C. The results showed that nitridation occurred in all the environments containing nitrogen. The nitridation attack was strongly influenced by the alloy compositions and the type of oxide formed (i.e., chromia or alumina), as some degree of oxidation was expected in the environments in which residual oxygen was present. Thermal cycling is briefly discussed because the integrity of protective oxides is also an important factor in resisting high-temperature oxidation and nitridation attack.

An attempt is being made to develop novel Ni-Mo-W-Cr-Al-X alloys with ICME approach with critical experimental/simulations and processing/microstructural characterization/property evaluation and performance testing has been adopted. In this work, based on thermodynamic modeling five alloy compositions with varying Mo/W and two alloys with high tungsten modified with the addition of Al or Ti were selected and prepared. The newly developed alloys were evaluated for their response to thermal aging in the temperature range of 700 to 850 °C and corrosion in the KCl-NaCl-MgCl 2 salt under suitable conditions. Thermally aged and post-corrosion test samples were characterized to ascertain phase transformations, microstructural changes and corrosion mechanisms. Al/Ti modified alloys showed significant change in hardness after 400 hours aging at 750°C, which was found to be due to the presence of fine γ’/γ” precipitates along with plate-shaped W/Mo-rich particles. These alloys show comparable molten salt corrosion resistance as commercial alloys at 750°C for 200-hour exposures. The good corrosion behavior of these alloys may be attributed to the formation of a protective multicomponent Al-or Ti-enriched oxide as well as the unique microstructure.

Creep-fatigue tests strain-controlled with different strain amplitudes and different hold times at 725 were done on nickel-based alloy 617 as a typical candidate material for turbine rotor of advanced ultra-supercritical power plant. Stress relaxes during the hold time when the strain remains at the tensile peak. The analysis of the stress relaxation during different strain hold times shows that the ratio of the relaxation stress and the maximum stresses has strong correlation with strain amplitude and hold time. The failure life also has a certain dependence on the relaxation stress ratio. The failure life decreases and the relaxation stress ratio increases as the strain amplitude increases. The failure life decreases and the relaxation stress ratio increases as the hold time increases. Therefore the stress relaxation ratio was used as an intermediate variable to obtain the corresponding relationship model by establishing the relationship between the relaxation stress ratio and the strain and the relationship between the relaxation stress ratio and the failure life. This model can be used to predict the creep-fatigue interaction life more simply and directly.