The measurement of damage from high temperature solid particle erosion (HTSPE) can be a lengthy process within the laboratory with many lab-based systems requiring sequential heat and cooling of the test piece to enable mass and/or scar volume measurements to be made ex situ. Over the last few years a new lab-based system has been in development at the National Physical Laboratory which has the ability to measure the mass and volume change of eroded samples in situ without the need to cool the sample. Results have previously been shown demonstrating the in situ mass measurement, more recently the in situ volume measurement capability has been added and used to evaluate the erosion performance of additively manufactured materials. Selective laser melting (SLM) is an advanced manufacturing method which is growing in popularity and application. It offers the ability to manufacture low volume complex parts and has been used in rapid prototyping. As the technique has developed there is increasing interest to take advantage of the ability to manufacture complex parts in one piece, which in some case can be more cost and time effective than traditional manufacturing routes. For all the benefits of SLM there are some constraints on the process, these include porosity and defects in the materials such as ‘kissing bonds’, surface roughness, trapped powder and microstructural variation. These features of the processing route may have implications for component performance such as strength, fatigue resistance wear and erosion. To investigate this further SLM IN718 has been used to evaluate factors such as surface roughness, microstructure and morphology on the erosion performance as measured in situ and compared with conventional produced wrought IN718 material.

Diffusion bonding is a key manufacturing process for nucleation applications including compact heat exchangers. Accurately predicting the alloy's behavior during the diffusion bonding process presents challenges, primarily due to the intricate interplay of microstructural evolution and physical processes such as compressive loading, temperature history, and component migration. The current study develops a phase-field model designed to simulate the diffusion bonding in 316H stainless steel, a material with exceptional high-temperature strength, corrosion resistance and suitability to high-pressure conditions. Our model incorporates a multi-phase, multi-component framework that aligns the experimental observations with the grain growth and heterogeneous nucleation, where arbitrary external compressive load and temperature history are considered. The simulations focus on grain nucleation, growth, and microstructure evolutions across diffusion bonding line under a variety of temperature profiles, mechanical loads, and surface roughness conditions, mirroring experimental setups. Our model predicts consistent simulation results with experiments in terms of the grain size and distribution near the bonding area, offering a better understanding of the diffusion bonding mechanism and the manufacturing process for building reliable compact heat exchangers.

Supercritical carbon dioxide cooling during machining has been identified as an effective measure to mitigate the risk of stress corrosion cracking in materials utilized in the primary circuit of light water reactors, particularly in pressure vessel structural steels. This study aims to compare two different cooling methods, the novel supercritical carbon dioxide and conventional high pressure soluble oil, employed during both milling and turning processes for SA508 Grade 3 Class 2 and AISI 316L steels. As the surface conditions of materials are critical to fatigue properties, such as crack initiation and endurance life, the fatigue performance of both cooling methods for each process were then evaluated and the impact on properties determined. To compare the potential benefits of supercritical carbon dioxide cooling against conventional soluble oil cooled machining, fatigue specimens were machined using industry relevant CNC machine tools. Surface finish and machining methods were standardized to produce two different specimen types, possessing dog- bone (milled) and cylindrical (turned) geometries. Force-controlled constant amplitude axial fatigue testing at various stress amplitudes was undertaken on both specimen types in an air environment and at room temperature using a stress ratio of 0.1. The fatigue performance of the supercritical carbon dioxide cooled specimens revealed substantially greater endurance lives for both SA508 and 316L materials, when compared with specimens machined using high pressure soluble oil cooling.

Extended storage of spent nuclear fuel (SNF) in intermediate dry cask storage systems (DCSS) due to lack of permanent repositories is one of the key issues for sustainability of the current domestic Light Water Reactor (LWR) fleet. The stainless steel canisters used for storage in DCSS are potentially susceptible to chloride-induced stress corrosion cracking (CISCC) due to a combination of tensile stresses, susceptible microstructure, and a corrosive chloride salt environment. This research assesses the viability of the cold-spray process as a solution to CISCC in DCSS when sprayed with miniature tooling within a characteristic confinement in two different capacities: cleaning and coating. In general, the cold-spray process uses pressurized and preheated inert gas to propel powders at supersonic velocities, while remaining solid-state. Cold-spray cleaning is an economical, non-deposition process that leverages the mechanical force of the propelled powders to remove corrosive buildup on the canister, whereas the cold spray coating process uses augmented parameters to deposit a coating for CISCC repair and mitigation purposes. Moreover, both processes have the potential to induce a surface compressive residual stress that is known to impede the initiation of CISCC. Surface morphology, deposition analysis, and microstructural developments in the near-surface region were examined. Additionally, cyclic corrosion testing (CCT) was conducted to elucidate the influence of cold-spray cleaning and coating on corrosion performance.

The power industry has been faced with continued challenges around decarbonization and additive manufacturing (AM) has recently seen increased use over the last decade. The use of AM has led to significant design changes in components to improve the overall efficiency of gas turbines and more recently, hot-section components have been fabricated using AM nickel-base superalloys, which have shown substantial benefits. This paper will discuss and summarize extensive studies led by EPRI in a novel AM nickel-base superalloy (ABD·900-AM). A comprehensive high temperature creep testing study including >67,000 hours of creep data concluded that ABD-900AM shows improved properties compared to similar ~35% volume fraction gamma prime strengthened nickel-base superalloys fabricated using additive methods. Several different creep mechanisms were identified and various factors influencing high temperature behavior, such as grain size, orientation, processing method, heat treatment, carbide structure, chemistry and porosity were explored. Additional studies on the printability, recyclability of powder, wide range of process parameters and several other factors have also been studied and results are summarized. A summary on the alloy -by-design approach and accelerated material acceptance of ABD-900AM through extensive testing and characterization is further discussed. Numerous field studies and examples of field use cases in ABD-900AM are also evaluated to showcase industry adoption of ABD-900AM.

For higher efficiency and competitive overall performance, it would be an advantage to be able to safely exceed the highest operational values, currently up to about 600-620°C/25-30 MPa in supercritical (SC) boiler plants. Under such operating conditions the oxidation resistance in SC water tends to limit the potential for further improvement of efficiency. The way to increase the oxidation resistance of traditional austenitic boiler tubes e.g. TP 347H is to do additional cold work on the boiler tube inner surface. In the current paper the effect of cold work on the oxidation resistance of TP347H and TP347HFG has been evaluated by shot peened samples with different parameters and subjecting those samples to supercritical oxidation exposure. The results show an improvement in the oxidation resistance of the alloys, especially in the large grained alloy TP347H. Also the uniformity of the deformation layer was seen to have an influence on the oxidation resistance, since the oxide nodules start to grow at locations with the thinnest or no deformation layer.

The efforts of the European Union and Germany in particular to realize the transformation towards a climate-neutral economy over the coming decades have the establishing of a hydrogen economy as a fundamental milestone. This includes production, import, storage, transportation and utilization of great amounts of gaseous hydrogen in existing and new infrastructure. Metallic materials, mainly steels, are the most widely used structural materials in the various components of this supply chain. Therefore, the accelerated use of hydrogen requires the qualification of materials (i.e., ensuring they are hydrogen-ready) to guarantee the sustainable and safe implementation of hydrogen technologies. However, there is currently no easily applicable and standardized method to efficiently determine the impact of gaseous hydrogen on metallic materials. The few existing standards describe procedures that are complex, expensive, and only available to a limited extent globally. This article outlines the key milestones towards standardizing an efficient testing method as part of the TransHyDE flagship project. This new approach enables testing of metallic materials in gaseous hydrogen using tubular specimens. It uses only a fraction of the hydrogen required by the traditional autoclave method, significantly reducing costs associated with technical safety measures. Among the topics to be discussed are the factors influencing the test procedure, including geometrical considerations, surface quality, gas purity and strain rate.

Diode laser cladding (DLC) surfaces, valued in the nuclear industry for their wear resistance, corrosion protection, and oxidation resistance, present unique challenges in surface characterization compared to conventionally machined surfaces. While traditional machined surfaces exhibit predictable, periodic topographies that can be validated through simple linear profile measurements, DLC surfaces feature distinctive metal tracks with central peaks and inter-track troughs, creating a wave-like structure with randomly distributed spherical asperities. This complex topography cannot be adequately characterized by traditional single-trace sampling methods due to significant variations in localized features at peaks and troughs. To address this challenge, this study examines DLC surfaces produced under varying control parameters (laser power, head travel speed, powder feed rate, and track offset) using laser confocal microscopy. Both profile and areal surface measurements are compared to identify the most effective method for characterizing DLC surface structure and quality, providing a foundation for standardized quality assessment in industrial applications.

For the safe life prediction of components under high cycle fatigue loading at high temperature, such as gas turbine blades and turbocharger components, the behavior of initial defects, which are physically short cracks below the long crack threshold ΔK is of crucial importance. The evolution of different crack closure mechanisms (such as plasticity, roughness and oxide induced crack closure) can lead to crack arrest by a reduction of the effective crack tip loading. To visualize the crack growth behavior of such cracks, cyclic crack resistance curves (cyclic R-curves) are used. The experimental determination of cyclic R-curves is challenging, especially under high temperature conditions due to a lack of optical accessibility. The formation of very short cracks in high strength materials makes it even more complicated to reliably determine these data. Within this study the crack growth behavior of physically short fatigue cracks in three different material states of the nickel alloy IN718 (wrought, cast and PBF-LB/M - processed) is experimentally determined at 650 °C. Based on a load increase procedure applied on Single Edge Notched (SEN) specimens with a compression pre-cracking procedure in advance, crack propagation of physically short cracks is measured with alternating current potential drop systems in air and under vacuum conditions. These examinations are carried out for three different load ratios (R = -1, 0 and 0.5) to investigate the amount of certain crack closure mechanisms active under different loading conditions. Moreover, the formation of a plastic wake along the crack flanks is determined by a finite element simulation. The results determined in air and under vacuum conditions are used to describe the impact of oxide induced crack closure on the behavior of physically short cracks. This allows the evaluation of the behavior of both near-surface and internal defects that are not accessible to the atmosphere.

To improve the efficiency of fossil fuel power plants the operating temperatures and pressures need to be increased. However, at high temperatures the steam side oxidation resistance becomes a critical issue for the steels used especially at the final stages of superheaters and reheaters. Apart from the chemical composition of the material, surface condition is a major factor affecting the oxidation resistance in steam and supercritical water. In this paper, stainless boiler steels (UNS S34710, S31035, S31042, and S30942) are investigated for oxidation resistance in flowing supercritical water. Tests were conducted in an autoclave environment (250 bar, with 125 ppb dissolved oxygen and a pH of 7) at 625°C, 650°C and 675°C for up to 1000 h. Materials were tested with as-delivered, shot peened, milled or spark eroded and ground surface finish. The results show a strong influence of surface finish at the early stages of oxidation. Oxides formed on cold worked surfaces were more adherent and much thinner than on a spark eroded and ground surface. This effect was stronger than the influence of temperature or alloy composition within the tested ranges.

Hardfacing alloys are commonly used for wear- and galling-resistant surfaces for mechanical parts under high loads, such as valve seats. Cobalt-based Stellite, as well as, stainless-steel-based Norem02 and Tristelle 5183 alloys show similar microstructural features that correlate with good galling resistance. These microstructures contain hard carbides surrounded by a metastable austenite (fcc) phase that transform displacively to martensite (hcp or bcc or bct) under deformation. As a result, the transformed wear surface forms a hard layer that resists transition to a galling wear mechanism. However, at elevated temperature (350°C), the stainless steel hardfacing alloys do not show acceptable galling behavior, unlike Stellite. This effect is consistent with the loss of fcc to bcc/bct phase transformation and the increase in depth of the heavily deformed surface layer. Retention of high hardness and low depth of plastic strain in the surface tribolayer is critical for retaining galling resistance at high temperature.

NAC International Inc. (NAC) is providing transportable storage canisters (TSCs) to Central Plateau Cleanup Company CPCCo) for long term dry storage of capsulized radioactive waste at the Hanford Site in Richland, WA. The TSC consists of 316/316L stainless-steel components welded to form a cylindrical canister that acts as a confinement boundary for the payload. The heat affected zones of the welded areas are most susceptible to Chloride Induced Stress Corrosion Cracking (CISCC), that may limit the life of the TSC. To mitigate CISCC during the anticipated 300-year storage period, an overcoating is applied to the heat affected zones of all external TSC fabrication welds, referred to as Cold Spray. This paper will discuss the purpose, development, and application of Cold Spray to the CPCCo TSCs. Cold Spray is a process whereby metal powder particles are deposited upon a substrate by means of ballistic impingement via a high-velocity stream of gas, resulting in a uniform deposition with minimal porosity and high bond strength. Temperatures are below the melting thresholds of many engineering materials enabling a large variety of application uses. NAC developed a process for Cold Spray application onto the 316/316L stainless-steel TSCs to serve as a CISCC protective/mitigative coating for its canister products. Testing during development arrived at nickel as the deposited coating material and nitrogen as the gas vehicle, along with a set of various application parameters. The qualified process was implemented onto the CPCCo TSCs. Prior to application, the equipment and process are validated via coupons that are sprayed and then tested to meet requirements for adhesion strength (ASTM C633) and porosity (ASTM E2109). After successful coupon testing, Cold Spray is performed on the external TSC fabrication welds, to include heat affected zones. Acceptance testing of the resulting deposition is performed via visual inspection.

This paper discusses the design of a prototype for accurately inspecting the degree of wall thinning in boiler tubes, which plays a critical role in power plants. The environment in power plants is characterized by extreme conditions such as high temperatures, high pressure, and ultrafine dust (carbides), making the maintenance and inspection of boiler tubes highly complex. As boiler tubes are key components that deliver high-temperature steam, their condition critically affects the efficiency and safety of the power plant. Therefore, it is essential to accurately measure and manage the wall thinning of boiler tubes.

The current work presented a study of isothermal-oxidation behavior of the additive manufactured (AM) Alloy718 in air at 800°C. The oxidation behavior of Alloy718 specimens produced by selective laser melting (SLM) and electron beam melting (EBM) process were comparatively examined. No significant differences were observed in oxidation kinetics while different microstructures of the oxide scale were found. Coarse and columnar chromia grains developed on SLM specimens, whereas the chromia scale of EBM specimens consisted of extremely fine grains. Glow Discharge Optical Emission Spectrometry (GD-OES) analysis revealed that SLM specimens contain a higher content of Ti in chromia compared with EBM specimens. Process-induced supersaturation in SLM specimens might lead to a relatively high concentration of Ti in the chromia, which may affect the grain morphology of oxide scale in the SLM specimen.

While the water vapor content of the combustion gas in natural gas-fired land based turbines is ~10%, it can be 20-85% with coal-derived (syngas or H 2 ) fuels or innovative turbine concepts for more efficient carbon capture. Additional concepts envisage working fluids with high CO 2 contents to facilitate carbon capture and sequestration. To investigate the effects of changes in the gas composition on thermal barrier coating (TBC) lifetime, furnace cycling tests (1h cycles) were performed in air with 10, 50 and 90 vol.% water vapor and in CO 2 -10%H 2 O and compared to prior results in dry air or O 2 . Two types of TBCs were investigated: (1) diffusion bond coatings (Pt diffusion or simple or Pt-modified aluminide) with commercially vapor-deposited yttria-stabilized zirconia (YSZ) top coatings on second-generation superalloy N5 and N515 substrates and (2) high velocity oxygen fuel (HVOF) sprayed MCrAlYHfSi bond coatings with air-plasma sprayed YSZ top coatings on superalloy X4 or 1483 substrates. In both cases, a 20-50% decrease in coating lifetime was observed with the addition of water vapor for all but the Pt diffusion coatings which were unaffected by the environment. However, the higher water vapor contents in air did not further decrease the coating lifetime. Initial results for similar diffusion bond coatings in CO 2 -10%H 2 O do not show a significant decrease in lifetime due to the addition of CO 2 . Characterization of the failed coating microstructures showed only minor effects of water vapor and CO 2 additions that do not appear to account for the observed changes in lifetime. The current 50°-100°C de-rating of syngas-fired turbines is unlikely to be related to the presence of higher water vapor in the exhaust.

Electron beam melting (EBM) is one of the candidate manufacturing processes for TiAl alloys which have been considered as next generation high-temperature structural materials. The microstructure and mechanical properties of Ti-48Al-2Cr-2Nb (48-2-2) alloy bars fabricated using EBM were investigated, with a particular focus on the effect of processing parameters such as input energy density and building direction. We observed that the microstructure of the alloy bars fabricated using EBM depends strongly on the processing parameters used during the fabrication process of alloy. In particular, the alloy bars fabricated under appropriate processing parameters have a unique layered microstructure composed of duplex regions and equiaxed γ-grain regions (γ bands). Because of their fine microstructure and deformable soft γ bands, the alloy bars with the unique layered microstructure exhibit higher strength and higher ductility at room temperature (RT) than that of cast alloys. In addition, the alloy bars fabricated at an angle between the building direction and the loading axis of 45° show good fatigue properties at RT even without hot isostatic pressing treatment.

Advanced Ultra-Super-Critical (A-USC) technology is one of the remarkable technologies being developed to reduce CO 2 emissions. The 700°C class A-USC steam turbine project was launched in 2008 to contribute to substantial reductions in CO 2 emissions and major Japanese manufacturers of boilers and turbines joined forces with research institutes to bring the project to reality. The use of Ni-base alloys is necessary for high temperature component of 700°C class AUSC steam turbine, and which is required increasing in size of Ni-base casting alloys to apply inner casing, valve body, nozzle block and so on. Therefore, trial production and verification test of Step block (weight: 1.7 ton) with actual component thickness 100-300mm were firstly performed to investigate basic casting material properties in this study. As candidate alloy, alloy 617 was chosen from a commercially available Ni-base alloy, from the viewpoint of large component castability and balance of mechanical properties stability at 700°C use. Microstructure test, high temperature mechanical test and long-term heating test of each thickness part specimen were carried out and good creep rupture strength was obtained. Next, the nozzle block of alloy 617 was manufactured for the trial casting of the actual machine mock-up component with complex shape (weight: 1.2 ton). For a comparison, alloy 625 was cast at the same time. Both castings of alloy 617 and alloy 625 were able to manufacture without a remarkable defect. Detailed comparisons to microstructures and mechanical properties are included in this paper.

This work describes the repair procedure conducted on the High Pressure/Intermediate Pressure (HP/IP) and generator rotors of a 180 MW steam turbine General Electric (GE) - STAG207FA type D11 installed at La Sierra Thermoelectric Power Plant in Puerto Nare, Colombia. A lubricant supply failure at base load caused severe adhesive damage to the shafts in the bearing support areas and a permanent 3.5 mm bow at the HP/IP rotor mid span section, which required a complex intervention. The repair process began with the identification of the rotors manufacturing material through in-situ metallographic replicas, handheld XRF analysis and surface hardness measurements. Volumetric manual Gas Tungsten Arc Welding (GTAW) welding reconstruction of cracked areas followed by a surface overlay using GTAW and Plasma Arc Welding (PAW) welding processes were applied with a modular mechanized system, where a stress relief treatment through vibration was implemented with the help of computational simulations carried out to determine the fundamental frequencies of the rotors. Geometric correction of the HP/IP rotor mid span section was achieved thanks to the excitation of the rotor at some fundamental frequencies defined by the dynamic modeling and the use of heat treatment blankets at specific locations as well. Finally, after machining and polishing procedures, the power unit resumed operation eleven months after the failure and remains in service to the present date.

The steam oxidation behaviour of boiler tubes and steam piping components is a limiting factor for improving the efficiency of the current power plants. Spallation of the oxide scales formed during service can cause serious damage to the turbine blades. Vallourec has implemented an innovative solution based on an aluminum diffusion coating applied on the inner surface of the T/P92 steel. The functionality of this coating is to protect the tubular components against spallation and increase the actual operating temperature of the metallic components. In the present study, the newly developed VALIORTM T/P92 product was tested at the EDF La Maxe power plant (France) under 167b and 545°C (steam temperature). After 3500h operation, the tubes were removed and characterized by Light Optical Metallography (LOM), Scanning Electron Microscopy (SEM), with Energy Dispersive X-ray spectrometry (EDX) and X-Ray Diffraction (XRD). The results highlight the excellent oxidation resistance of VALIORTM T/P92 product by the formation of a protective aluminum oxide scale. In addition, no enhanced oxidation was observed on the areas close to the welds. These results are compared with the results obtained from laboratory steam oxidation testing performed on a 9%Cr T/P92 steel with and without VALIORTM coating exposed in Ar-50%H 2 O at 650°C.

Monoblock low-pressure (LP) turbine rotor shaft forgings for nuclear power plants have been produced from up to 600 ton ingots. However, ingots greater than 600 tons are necessary to increase the generator capacity. Segregation, non-metallic inclusions, and micro porosities inevitably increase with the increase in ingot size. Manufacturing such massive ingots with high soundness is quite difficult. Thus, the development of 650 ton ingot production was carried out in 2010. The 650 ton ingot was dissected and investigated to verify its internal quality. The internal quality of the 650 ton ingot was found to be equal to that of 600 ton ingots. Subsequently, in 2011, we produced a 670 ton ingot, the world’s largest, to produce a trial LP rotor shaft forging with a diameter of 3,200 mm. Results show that the internal quality, mechanical properties, and heat stability are the same as LP rotor shaft forgings made from 600 ton ingots.