Due to a high degree of mixing between substrate and weld deposit, fusion welding of dissimilar metal joints functionally produce new, uncharacterized alloys. In the power generation industry, such mixing during the application of cobalt-based hardfacing has led to a disconcerting number of failures characterized by the hard overlay welds disbonding. Investigations into this failure mechanism point to the unknown alloy beneath the surface of the hardfacing layer transforming, hardening, and becoming brittle during service. This research describes a methodology for exploring a chemical space to identify alloy combinations that are expected to be safe from deleterious phase formation. Using thermodynamic modeling software and a stepped approach to potential chemistries, the entire phase stability space over the full extent of possible mixing between substrate and weld material can be studied. In this way diffusion effects – long term stability – can also be accounted for even in the case where mixing during application is controlled to a low level. Validation of predictions specific to the hardfacing system in the form of aged weld coupons is also included in this paper. Though the application of this methodology to the hardfacing problem is the focus of this paper, the method could be used in other weld- or diffusion- combinations that are expected to operate in a high temperature regime.

Haynes 282 is a great candidate to meet advanced ultra-super-critical (A-USC) steam conditions in modern coal-fired power plants. The standard 2-step aging treatment has been designed for optimizing microstructure therefore providing excellent mechanical properties. We studied an alternative, more economical, 1-step aging treatment and compared microstructure, tensile properties at 750˚C and deformation behavior. Moreover, three cooling rates from the solution temperature were studied to simulate large-scale components conditions. We found that as much as about 20% of fine spherical intragranular γ' particles were successfully precipitated in all cases. Their average size increased as the cooling rate decreased. All four heat-treated alloys exhibited good mechanical properties at 750˚C with a yield strength well over 620MPa. As expected, the yield strength increased and the ductility decreased as the average γ' size decreased. The alloys exhibited a mixed mode of deformation, though the dominant deformation mechanism depended on the different γ' characteristics. The major operative deformation mechanism could be well predicted by strength increment calculations based on the precipitation strengthening model. Our results suggest that wrought Haynes 282 produced by a more economical 1-step aging treatment may be a reliable candidate for high temperature applications under A-USC conditions.

An iron aluminide (Fe 3 Al) intermetallic coating was deposited onto F22 (2.25Cr-1Mo) steel substrate using a JP-5000 high velocity oxy-fuel (HVOF) thermal spray system. The as-sprayed coating was characterized by electron microscopy, X-ray diffraction, oxidation, and adhesion. Fe 3 Al coated steel specimens were exposed to a mixed oxidizing/sulfidizing environment of N 2 -10%CO-5%CO 2 -2%H 2 O-0.12%H 2 S (by volume) at 500, 600, 700, and 800°C for approximately seven days. All specimens gained mass after exposure, inversely proportional to temperature increases. Representative cross-sectioned specimens from each temperature underwent scanning electron microscopy (SEM) and X-ray mapping examination. Results are presented in terms of corrosion weight gain and product formation. The research evaluated the effectiveness of an HVOF-sprayed Fe 3 Al coating in protecting a steel substrate exposed to a fossil energy environment.

Materials are the key to develop advanced ultra-supercritical (A-USC) steam generators. Operating at temperature up to 760°C and sustained pressure up to 4500 psi. Pressure vessel and piping materials may fail due to creep, oxidation, and erosion. Valves are particularly subjected to loss of function and leakage due to impermeant of the sealing surfaces. New materials, less susceptible to the above damage modes are needed for A-USC technology. Two Ni-based superalloys have been identified as prime candidates for valves based materials. Hardfacing is applied to sealing surfaces to protect them from wear and to reduce friction. Stellite 6 (Cobalt-based alloy) is the benchmark hardfacing owing to its anti-galling properties. However, the latest results tend to indicate that it is not suitable for high pressure application above 700°C. An alternative hardfacing will be required for A-USC. New Ni- and Co- based alloys are being developed for applications where extreme wear is combined with high temperatures and corrosive media. Their chemistry accounts for the excellent dry-running properties of these alloys and makes them very suitable for use in adhesive (metal-to- metal) wear. These new alloys have better wear, erosion, and corrosion resistance than Stellite 6 in the temperature range 800°C ~ 1000°C. As such, they have the potential to operate in A-USC. Velan recently developed an instrumented high temperature tribometer in collaboration with Polytechnique Montreal to characterize new alloys including static and dynamic coefficients of friction up to 800°C. We present herein the methodology that has been devolved to explore the effects of elevated temperature on the tribological behavior of those advanced material systems, with the goal of capturing the basis for the specification, design, fabrication, operation, and maintenance of valves for A-USC steam power plants.

Creep strength enhanced ferritic (CSEF) steels, particularly modified 9Cr steels Grade 91 and 92, are increasingly used in advanced coal-fired power plants for header and steam piping construction. While these materials typically enter service after receiving a standard high-temperature normalizing treatment followed by lower temperature tempering to achieve optimal microstructure, practical situations like welding operations may expose components to additional heat treatment exceeding the Ac 1 , and potentially the Ac 3 , temperature before returning to tempering temperature. This research examines the effects of simulated post weld heat treatments (PWHT) on Grade 91 and 92 materials using dilatometer-controlled heating and cooling rates, with peak temperatures below Ac 1 , between Ac 1 and Ac 3 , and above Ac 3 , followed by heat treatment at 750°C for 2 hours. Hardness measurements revealed significant reduction when exceeding the Ac 1 temperature, while advanced electron microscopy, including electron back scatter diffraction, was employed to analyze changes in martensite laths and grain structure, along with detailed carbide size distribution analysis using both scanning and transmission electron microscopy. The findings are discussed in terms of how such PWHT overshoots might affect mechanical properties during high-temperature service.

This paper introduces the GKM (Grosskraftwerk Mannheim AG) test rig, designed to evaluate new Ni-based alloys and austenitic steels for components in advanced 700°C power plants under real operational conditions. The test rig, integrated into a conventional coal-fired power plant in Mannheim, Germany, simulates extreme conditions of up to 725°C and 350/200 bar pressure. After approximately 2000 hours of operation, the paper presents an overview of the rig's design, its integration into the existing plant, and the status of ongoing tests. It also outlines parallel material investigations, including creep rupture tests, mechanical-technological testing, and metallurgical characterization. This research is crucial for the development of materials capable of withstanding the severe conditions in next-generation power plants, potentially improving efficiency and performance in future energy production.

Over the past two decades there has been considerable interest in the development of coatings with finer microstructures approaching nanometer scale because these coatings are more resistant to high-temperature oxidation and corrosion than their counterpart conventional coatings. Long-term cyclic oxidation behavior of nanocrystalline FeCrNiAl and NiCrAl coatings were evaluated at different temperatures and the results showed that ultra-fine grain structure promoted selective oxidation of Al during thermal exposure. The protective Al2O3 scale formed on these coatings with Al content as low as 3 wt.% and exhibited excellent spallation resistance during thermal cycling. The nanocrystalline NiCrAl coating showed significantly higher oxidation resistance compared to the conventional plasma sprayed NiCoCrAlY and PWA 286 coatings. However, the Al content in the nanocrystalline coatings was consumed in relatively short time due to inward and outward diffusion of Al. Variation of oxide-scale spallation resistance during thermal cycling and the rate of Al consumption between the nanocrystalline and plasma sprayed coatings are compared.

High-temperature shape memory alloys (HTSMAs) are expected to be utilized for actuators in high temperature environments such as thermal power plants and jet engines. NIMS has designed TiPd shape memory alloys because high martensitic phase transformation temperature of TiPd around 570 ° C is expected to be high-temperature shape memory alloys. However, the strength of the austenite phase of TiPd is low and the perfect recovery was not obtained. Then, strengthening of TiPd by addition of alloying elements has been attempted, but the complete recovery was not obtained. Therefore, high entropy alloys (HEA, multi-component equiatomic or near equiatomic alloys) were attempted for HTSMA. The severe lattice distortion and the sluggish diffusion in HEA are expected to contribute strong solid-solution hardening of HTSMA. In this study, multicomponent alloys composed of Ti-Pd-Pt-Ni-Zr were prepared and the phase transformation, shape memory properties, and mechanical properties were investigated.

Local vacuum electron beam welding is an advanced manufacturing technology which has been investigated at Sheffield Forgemasters to develop as part of a cost-effective, reliable, agile, and robust manufacturing route for the next generation of civil nuclear reactors in the UK. A dedicated electron beam welding facility at Sheffield Forgemasters has been installed. This includes an x-ray enclosure, 100kW diode electron gun, 100T turntable, and weld parameter development vacuum chamber. A small modular reactor demonstrator vessel has successfully been manufactured with a wall thickness of 180 mm, including indication-free slope-in, steady- state and slope-out welding parameters. Electroslag strip cladding has also been investigated to demonstrate its viability in reactor pressure vessel manufacture. The electro-slag strip cladding method has been shown to produce high quality 60 mm strips on a 2600 mm inner diameter ring.

Refractory metal, such as molybdenum and tungsten, are used in increasingly severe environments. Therefore, these materials are required to have superior mechanical properties, long life and excellent reliability. In this study, we developed newly Mo alloy dispersed Mo-base intermetallic compound for material forming such as hot extrusion die. This newly Mo alloy “MSB” exhibited superior mechanical properties compared with convention Mo alloy at temperatures below 1000℃. In addition, by adding a titanium alloy to the MSB, we have developed another alloy “T-MSB” that has high mechanical properties at higher temperatures. In the hot extrusion of brass, die made of these Mo alloys had 2.5 times longer tool life than the conventional Mo alloy die.

The long-term performance of superheater super 304h tube during the normal service of an ultra-supercritical 1000mw thermal power unit was tracked and analyzed, and the metallographic structure and performance of the original tube sample and tubes after 23,400h, 56,000h, 64,000 h, 70,000 h and 80,000 h service were tested. The results show that the tensile strength, yield strength and post-break elongation meet the requirements of ASME SA213 S30432 after long-term service, but the impact toughness decreases significantly. The metallographic organization is composed of the original complete austenite structure and gradually changes to the austenite + twin + second phase precipitates. With the extension of time, the number of second phases of coarseness in the crystal and the crystal boundary increases, and the degree of chain distribution increases. The precipitation phase on the grain boundary is dominated by M 23 C 6 , and there are several mx phases dominated by NbC and densely distributed copper phases in the crystal. The service environment produces a high magnetic equivalent and magnetic induction of the material, the reason is that there are strips of martensite on both sides of the grain boundary, and the number of martensite increases with the length of service.

The high-temperature oxidation of Fe-9Cr-1Mo steel in a CO 2 environment, with varying oxygen content (0.6-3%), was investigated at 700°C. While the steel heavily oxidized in pure CO 2 , the oxidation mass gain decreased significantly with increasing oxygen content. Microscopic analysis revealed the formation of Fe-rich nodules with an internal Cr-carbide layer beneath them. Notably, the number of nodules decreased with increasing oxygen content but remained independent of the oxidation time. To explain these observations, the authors propose that “intrinsic” defects within the initially formed protective Cr 2 O 3 scale facilitated gas permeation. This mechanism is believed to be responsible for the observed dependence of nodule formation on the oxygen content in the gas mixtures.

In this paper, the microstructural evolution of P92 steel were studied in the viewpoint of degradation mechanism based on the creep rupture experiment results obtained at elevated temperature by means of macroscopic, metallographic, electronic microscope, energy spectrum, XRD and TEM examination. The results show that the decrease of mechanical properties of P92 steel is mainly due to the change of microstructure and the transformation of carbides, and there is definite relationship between microstructure evolution, mechanical properties and life loss of P92 steel. The results are beneficial to the further study of mechanism of high temperature creep rupture strength and microstructural evolution of heat-resistant steel. It also has important instructive significance to quantitative identification of scientific selection of materials.

This study explores the expanded applications of Alloy J513, a high-performance material traditionally used in cast engine valvetrain components, for powder metallurgy and surface cladding applications. While already recognized for its superior heat and wear resistance at a lower cost compared to cobalt-based hardfacing materials, J513 demonstrates additional advantages in powder metallurgy applications due to its ability to achieve desired powder characteristics through atomization without requiring post-atomization annealing. Through experimental investigation based on fundamental metallurgical principles and cladding engineering processes, the presented research demonstrates J513’s exceptional weldability and favorable weldment structure compared to conventional cobalt-based alloys. The study establishes crucial relationships between weldment behavior and unit energy input, providing valuable insights for advanced cladding techniques while highlighting J513’s potential as a sustainable alternative to traditional nickel- and cobalt-based alloys in various manufacturing processes, including surface overlay and additive manufacturing.

Alumina-forming austenitic stainless steels (AFAs) are potential materials for boiler/steam turbine applications in next generation fossil fuel power plants. They display a combination of good high temperature creep strength, excellent oxidation resistance and low cost. A recently-developed AFA alloy based on Fe-14Cr-32Ni-3Nb-3Al-2Ti (wt.%) shows better creep performance than a commercially-available Fe-based superalloy. In this paper we used scanning electron microscopy and transmission electron microscopy to study the fracture surfaces and cracking behavior in relation to the precipitates present in creep failure samples of this alloy tested at either 750°C/100 MPa or 700°C/170 MPa. It was found that most cracks are formed along the grain boundaries with precipitate-free zones beside the grain boundaries potentially providing the path for propagation of cracks.

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.

India's current installed power generating capacity is about 225,000 MW, of which about 59% is coal based. It is projected that India would require an installed capacity of over 800,000 MW by 2032. Coal is likely to remain the predominant source of energy in India till the middle of the century. India is also committed to reducing the CO 2 emission intensity of its economy and has drawn up a National Action Plan for Climate Change, which, inter alia, lays emphasis on the deployment of clean coal technologies. With this backdrop, a National Mission for the Development of Advanced Ultra Supercritical Technology has been initiated. The Mission objectives include development of advanced high temperature materials, manufacturing technologies and design of equipment. A corrosion test loop in an existing plant is also proposed. Based on the technology developed, an 800 MW Demonstration A-USC plant will be established. Steam parameters of 310 kg/cm 2 , 710 °C / 720 °C have been selected. Work on selection of materials, manufacture of tubes, welding trials and design of components has been initiated. The paper gives details of India's A-USC program and the progress achieved.

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.

In the “Boiler Materials for Ultrasupercritical Coal Power Plants” program, sponsored by the U.S. Department of Energy and the Ohio Coal Development Office, various materials are being assessed for their suitability in the high-temperature, high-pressure environment of advanced ultrasupercritical (A-USC) boilers. Beyond mechanical properties and fireside corrosion resistance, these materials must also exhibit adequate steamside oxidation and exfoliation resistance. A comprehensive database of steamside oxidation test results at temperatures relevant to A-USC conditions has been compiled over recent years. These tests have been conducted on ferritic and austenitic materials with chromium content ranging from 2 to 26%. The specimens were evaluated for oxidation kinetics and oxide morphology. The findings indicate that steamside oxidation behavior is significantly affected by temperature, the chromium content of the material, and the ability of chromium to diffuse through the material's crystallographic lattice structure. Additionally, surface treatments have been applied to enhance the steamside oxidation resistance of certain materials. While these treatments have shown potential, their effectiveness can be limited by the operational temperatures.

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.