bluuebunny/crossref_metadata_2025 huggingface dataset:
Creep and Creep Crack Behavior of Alloy C-263 Used for Thick-Walled Components—An Update
Authors: Mueller Falk , Oechsner Matthias , Speicher Magdalena , Klenk Andreas
Published: March 2024

Detailed knowledge of the creep and creep crack behavior is essential for a safe operation of thick-walled components in thermal power plants. High mechanical loads and temperatures of more than 700 °C often require the application of nickel-based alloys, e.g. alloy C-263. Unfortunately, manufacturing and non-destructive evaluation (NDE) of thick-walled components (> 50 mm) made of nickel-based alloys are quite challenging. Tolerable critical flaw sizes, experimentally validated for long service durations, play an important role in the quality assurance of such components. It is commonly accepted that manufacturing parameters, e.g. heat treatment procedures, have a significant influence on creep ductility and time-dependent crack behavior. By means of adjusting the process parameters, the ductility and the creep life of notched specimen can be significantly improved in the case of alloy C-263. Essential root cause is the decoration of grain boundaries with carbides which drastically influences creep crack initiation and growth. This results in significant differences for allowable critical flaw sizes and thus, the potential use of the candidate material. On a first generation of alloy C-263 “G1”, a dense population of carbides on the grain boundaries was found, which resulted in an inadmissible creep crack behavior. The resulting critical flaw sizes were only a few tenths of a millimeter. On a second generation “G2”, the grain boundary occupation was positively influenced, so that a satisfactory creep crack behavior could be found. The critical flaw sizes are in the order of one millimeter or more. A critical or impermissible material behavior under creep conditions can be demonstrated by testing smooth and notched round specimens. For example, the first generation “G1” notched round specimens fails earlier than the smooth round specimens, indicating notch sensitivity. On the second generation “G2”, however, a notch insensitivity was found. The critical defect sizes can be determined by a method that takes into account a simultaneous examination of the crack tip situation and the ligament situation.
Development of Pt-Ir Diffusion Coatings on Ni-Based Single Crystal Superalloys for Oxidation Protection
Authors: Murakami Hideyuki , Tue Dao Chi , Ishida Akira , Hayakawa Masao , Lien Le Thi Hong
Published: March 2024

A paste, which contains Pt or Pt-xIr (x = 0-30 at%) alloy nano-powder was sprayed on some Ni-based single crystal superalloys. Then the annealing diffusion treatment at 1100 °C for 1 h in flowing Ar atmosphere was conducted to develop Pt and Pt-Ir diffusion coatings. Cyclic oxidation tests were carried out at 1150 °C in still air in order to investigate the thermal stability and oxidation behavior of the coatings and they were compared with electroplated diffusion coatings. It was found that Ir can retard the formation of voids in both the coatings and substrates. In addition, by replacing the electroplating method to the paste coating method, the crack problem due to the brittle feature of electroplated Pt-Ir coatings could be solved. Therefore, the Pt-Ir diffusion coating prepared by the paste- coating method is promising as the bond-coat material due to suppression of voids, cracks and stable Al2O3 on the surface. The Pt-Ir paste diffusion coatings introduced above have several further advantages: they are easy to recoat, cause less damage to substrates, and offer comparable oxidation resistance. Thus, the method can be applicable to the remanufacturing of blades, which may extend the life of components. The future aspect of the paste coating will also be discussed.
Effects of Eta Phase on Creep Performance of the Nickel-Base Superalloy 263
Authors: Mohale N.R. , Milligan W.W. , Sanders P.G. , White C.L. , Shingledecker J.P. , Bridges P.A.
Published: March 2024

In wrought nickel-base alloys used at elevated temperatures for extended periods of time, it is commonly observed that unwanted phases may nucleate and grow. One such phase is the eta phase, based on Ni3Ti, which is a plate-shaped precipitate that nucleates at the grain boundaries and grows at the expense of the strengthening gamma prime phase. In order to study the effects of eta phase on creep performance, Alloy 263 was modified to contain 3 different microstructures: standard (contains gamma prime); aged (contains gamma prime and eta); and modified (contains only eta and no gamma prime). These microstructures were then creep tested in the range of 973-1123 K (700-850°C). An extensive test matrix revealed that the eta-only modified alloy had creep rupture strengths within 10% of the standard alloy even though this alloy had no strengthening gamma prime precipitates. It also exhibited superior creep ductility. A preliminary test matrix on the aged material containing eta and gamma prime prior to the creep tests revealed that the performance of this microstructure was generally between that of the standard alloy (best) and the eta-only alloy (worst). The aged material exhibited far superior creep ductility. These results suggest that the presence of the eta phase may not be deleterious to creep ductility, and in fact, may enhance it.
Effect of B Addition on Creep Strength of Low-C Austenitic Steels
Authors: Otaki Nao , Okada Hirokazu
Published: March 2024

Materials with a higher creep strength and sensitization resistance superior to those of 347AP are required in complex refinery such as delayed coker. To optimize material designing, the effect of B addition on the Z phase-strengthened steels has been investigated. B addition significantly improved the creep strength of steel containing Nb despite the absence of M23C6, whereas the creep strength of steel without Nb showed only a slight change with B addition. The size of Z phase was smaller in the Nb-containing steel with B content than that in B-free steel. It was suggested that the refinement of Z phase contributed to the creep strengthening by B addition in steels containing Nb.
The Dominant Factors of Creep Rupture Strength of 18Cr-9Ni-3Cu-Nb-N Steel
Authors: Hashimoto Keita , Arisue Ko , Saito Nobuhiko , Komai Nobuyoshi , Nagashima Erika , Tominaga Kimihoko , Fujita Masaaki
Published: March 2024

18Cr-9Ni-3Cu-Nb-N steel is widely used for heat exchanger tubes such as super-heaters and reheaters of ultra-super critical power generation boilers. In this study, long-term creep rupture tests were carried out on 18Cr-9Ni-3Cu-Nb-N seamless steel tubes of 7 heat materials, and the specimens of 2 heat materials with different creep rupture strengths were observed by ultra-low voltage scanning electron microscope after creep rupture tests. The results of the investigation of the creep rupture specimens and the coverage ratios of M23C6 on grain boundary were different. The cause of this was estimated to be the difference in B content between the 2 heat materials. Creep rupture tests with different final ST temperatures were also carried out using the same heat material, and it was revealed that the higher final ST temperature, the higher the creep rupture strength. As the final ST temperature is higher, the amount of Nb(C, N) solid solution in the matrix increases, and the amount of precipitation of NbCrN and M23C6 increases during creep, therefore it is assumed that the creep rupture strength increases.
Study on the Long-Term Performance of Super 304H Pipe in Superheater of Ultra Supercritical 1000 MW Power Unit
Authors: Xiong Wei , Ma Qiaochun , Fu Wangan , Shi Zhigang , Yin Zun , Yan Aijun
Published: March 2024

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 M23C6, 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.
Study on the Magnetic Nondestructive Testing Technology for Oxide Scales
Authors: Du Jingyi , Chen Kang , Wang Jiacheng , Hao Le , Qiao Yue , Teng Weizhong , Feng Ming , Liu Qingli , Yan Aijun
Published: March 2024

The spalling of oxide scales at the steam side of superheater and reheater of ultra-supercritical unit is increasingly serious, which threatens the safe and economic operation of the boiler. However, no effective monitoring method is proposed to provide an on-line real-time detection on the spalling of oxide scales. This paper proposes an on-line magnetic non-destructive testing method for oxide granules. The oxide scale-vapor sample from the main steam pipeline forms liquid-solid two-phase flow after the temperature and pressure reduction, and the oxide granules are separated by a separator and piled in the austenitic pipe. According to the difference of the magnetic features of the oxide scales and the austenitic pipe, the oxide granule accumulation height can be detected through the spatial gradient variations of the magnetic induction. The laboratory test results show that the oxide scale accumulation can be accurately calculated according to the spatial gradient changes around the magnetized oxide granules, with the detection error not exceeding 2%.
Root Cause Analysis of Boiler Final Superheater Bending Tube Failure
Authors: Tzeng C. W. , Kao C. S. , Chen T. T.
Published: March 2024

The broken elbow of the final superheater tube (ASME SA213 TP304H) from a coal-fired power plant was evaluated. The root causes were identified by metallographic observation, sensitization evaluation, hardness measurement, and EBSD analysis. The analysis results reached the following conclusions. (1) The tube bending was not performed in accordance with ASME Code requirements—a solid-solution heat treatment was not performed after cold working. (2) The hardness at the elbow is greater than 260 HV, exceeding the ASME code limit. (3) The sensitization was 19%, showing a performance degradation. (4) There are no obvious corrosion elements in the oxide layers of the cracks. (5) Metallographic microstructure analysis shows that there are many intergranular cracks and carbides such as Cr-rich phase and Fe-Cr are precipitated at the grain boundaries, ultimately resulting in strain-induced precipitation hardening damage.
Influence of Initial Precipitated γ′′ Phase Microstructure on δ-Phase Precipitation Behavior in Alloy 718
Authors: Otake Takuji , Nishimoto Takashi , Okajima Takuma
Published: March 2024

Alloy 718 is one of the most useful heat-resistant alloys for important device components that require high-temperature properties. In order to obtain excellent mechanical properties, it is necessary to form fine grains, for which the pinning effect of the δ phase can be used in some cases. To precipitate a sufficient amount for the pinning effect, time-consuming isothermal heat treatments are required. Thus, a metallurgical method with a shortened holding time would improve production efficiency considerably. Our goal is to optimize the forging process to control grain size by utilizing the δ phase, and the purpose of this study was to investigate the influence of the initial microstructure of the precipitated γ″ phase on δ-phase precipitation behavior in Alloy 718. As a solute treatment, Alloy 718 was heated at 1050 °C for 4 h, followed by heating of some samples at 870 °C for 10 h to precipitate the γ″ phase. The specimen with precipitated γ″ phase showed more precipitated δ phase than that under the solute condition by comparing results of heating at 915 °C. This suggested that utilizing the γ″ phase promoted δ-phase precipitation, and it is thus expected to shorten the heat treatment time for δ-phase precipitation.
A286 Applications in Turbo Machineries—Experiences in Fabrication, In-Service Evaluation, and Failure Analysis
Authors: Gowreesan Vamadevan , Greaves Wayne
Published: March 2024

The A286 is one of the earliest superalloys developed. It has been used for manufacturing different components of turbo machineries because of its balanced high temperature properties. These components include shafts, discs, spacers, blades and fasteners. This paper reviews some of the issues and recent field experiences related to metallurgy, fabrication, in-service evaluation and failure of some of these components. The fabrication aspects including the effects of alloy melting processes, forging parameters and different types of heat treatments on the processed parts are discussed. The importance of these factors on the microstructure and properties of A286 are highlighted. The effects of service exposure on some of these parts are also discussed. In service evaluation involves checking for service induced damage or changes in microstructures and properties so that the suitability of the part for continued service can be determined. The failure analysis section of the paper briefly discusses failures of two expander wheels and an expander disc made out of A286 to pinpoint some of the salient features of damage accumulation and fracture during service.
Microstructure and High-Temperature Strength in Cr-Si Binary Alloys
Authors: Aono Yuki , Omori Toshihiro , Kainuma Ryosuke
Published: March 2024

Cr-based alloys have potential as heat-resistant materials due to the higher melting point and lower density of Cr. Although oxidation and nitridation at high temperatures are one of the drawbacks of Cr and Cr-based alloys, addition of Si has been reported to enhance the oxidation and nitridation resistance. This study focuses on the microstructure and mechanical properties in the Cr-Si binary alloys with the Crss + Cr3Si two-phase structure. The Cr-16at.%Si alloy showed an eutectic microstructure and hypoeutectic alloys with the lower Si composition exhibited a combination of the primary Crss and the Crss/Cr3Si eutectic microstructure. Compression tests at elevated temperatures were conducted for the hypoeutectic and the eutectic alloys in vacuum environment. Among the investigated alloys, the Cr-13at.%Si hypoeutectic alloy including the Cr3Si phase of about 40% was found to show the highest 0.2% proof stress of 526 MPa at 1000 °C. Its specific strength is 78.1 Nm/g which is roughly twice as high as that of Ni-based Mar-M247 alloy. It was also confirmed that the 0.2% proof stress at 1000 °C depends on not only the volume fraction of the Cr3Si phase, but also the morphology of the Crss + Cr3Si two-phase microstructure.
Component Level Hot Corrosion and Deposit Modeling for Large Gas Turbines
Authors: Kulkarni Anand A. , Senga Masayoshi , Kiliani Stefan W. , Summer Joy , Simms Nigel J.
Published: March 2024

Modern gas turbines are operated with fuels that are very clean and within the allowances permitted by fuel specifications. However, the fuels that are being considered contain vanadium, sulfur, sodium and calcium species that could significantly contribute to the degradation of components in hot gas flow path. The main potential risk of material degradation from these fuels is “hot corrosion” due to the contaminants listed above combined with alkali metal salts from ambient air. Depending on the temperature regime hot corrosion can damage both TBC coatings and bond coat/substrate materials. Deposit-induced or hot corrosion has been defined as “accelerated oxidation of materials at elevated temperatures induced by a thin film of fused salt deposit”. For the initiation of hot corrosion, deposition of the corrosive species, e.g. vanadates or sulfates, is necessary. In addition to the thermodynamic stability, the condensation of the corrosive species on the blade/vane material is necessary to first initiate and then propagate hot corrosion. Operating temperatures and pressures both influence the hot corrosion damage. The temperature ranges over which the hot corrosion occurs depend strongly on following three factors: deposit chemistry, gas constituents and metal alloy (or bond coating/thermal barrier coating) composition. This paper reports the activities involved in establishing modeling and simulation followed by testing/characterization methodologies in relevant environments to understand the degradation mechanisms essential to assess the localized risk for fuel flexible operation. An assessment of component operating conditions and gas compositions throughout the hot gas paths of the gas turbines, along with statistical materials performance evaluations of metal losses for particular materials and exposure conditions, are being combined to develop and validate life prediction methods to assess component integrity and deposition/oxidation/corrosion kinetics.
Ultrahigh-Temperature Tensile Creep Behavior of 1st Generation MoSiBTiC Alloy
Authors: Yoshimi Kyosuke , Kamata Shiho Yamamoto , Yanagiya Ryuta , Ida Shuntaro , Uemura Sojiro , Tsurekawa Sadahiro
Published: March 2024

The cast microstructure of 1st generation MoSiBTiC alloy composed of Mo solid solution (Moss), Mo5SiB2, TiC phases largely affects tensile-creep behavior in the ultrahigh temperature region. Mo5SiB2 phase crystallized during solidification is plate-like with a size of several tens of microns. The plate surface is parallel to the (001) basal plane, and the <100] directions preferentially grow along the cooling direction, and thereby Mo5SiB2 has a strong texture while Moss and TiC show randomly-oriented distribution in a cast ingot. During creep, Mo5SiB2 plates are largely rotated and Moss works as sticky ligament in the small-plate-reinforced metal-matrix composites. This may be the reason why the MoSiBTiC alloy exhibits large creep elongation and excellent creep resistance. In other words, the evolution of microstructures infers that the consummation of Mo5SiB2 plate rotation may lead to the initiation of creep rapture process. Therefore, the unique microstructure formed during solidification provides the feature of good mechanical properties for the 1st generation MoSiBTiC alloy.
Creep Behavior of Near-α Ti-Al-Nb-Zr Alloys
Authors: Yamabe-Mitarai Yoko , Shimagami Kei , Masuyama Haruki , Matsunaga Tetsuya , Toda Yoshiaki , Ito Tsutomu
Published: March 2024

Ti alloys are used as compressor blades and disks in jet engines due to their high specific strength and good oxidation resistance at operation temperature. However, Ti alloys cannot be used above 600 °C because creep properties and oxidation resistance deteriorate. To overcome the above problems, the effect of alloying element on oxidation resistance was investigated and it was found that Sn deteriorated oxidation resistance and Nb improved oxidation resistance. Then, we have attempted to design new Ti alloys without Sn, but including Nb because Nb improved oxidation resistance. To expect solid-solution hardening, Zr was also added to the alloys. In this study, the creep behavior of Ti-10Al-2Nb-2Zr and Ti-10Al-2Nb-2Zr-0.5Si alloys was investigated. The creep test was performed at temperature range between 550 and 650 °C and stress range between 137 and 240 MPa. The stress exponent and the activation energy for creep were analyzed using an Arrhenius equation. The stress exponent was 5.9 and 3.4, and the activation energy was 290 and 272 kJ/mol for Ti-10Al-2Nb-2Zr and Ti-10Al-2Nb-2Zr-0.5Si, respectively. This indicates the creep deformation mechanism is dislocation (high-temperature power law) creep governed by lattice diffusion.
Microstructure Evolution and High-Temperature Strength of Thermomechanical Processed Near-α Ti Alloys
Authors: Masuyama Haruki , Shimagami Kei , Ito Tsutomu , Shimojo Masayuki , Yamabe-Mitarai Yoko
Published: March 2024

Understanding of the thermomechanical processing that affects microstructures is important to develop new alloys, because the mechanical properties of Ti alloys depend on the microstructures. In our previous study, we found Sn deteriorated the oxidation resistance, while Nb improved the oxidation resistance. Then, we have focused on Ti-Al-Nb-Zr alloys which Nb was added instead of Sn. Zr was added for solid solution strengthening. In this study, the formation of microstructures by thermomechanical processing and the effect of microstructure on the mechanical properties were investigated using the Ti-13Al-2Nb-2Zr (at%) alloy. The samples heat-treated in the β+α phase followed by furnace cooling after processed in the β+α phase formed the equiaxed or the ellipsoid α phase surrounded by the β phase. On the other hand, the sample heat-treated in the β+α phase followed by furnace cooling after processed in the β phase formed the lamellar microstructure. The compression strengths of the equiaxed α structure processed at two temperatures in the β+α phase were almost the same. While creep life of the bi-modal structure was drastically changed by processing temperature.
High-Temperature Shape Memory Effect of High Entropy Alloys
Authors: Matsuda Hiromichi , Sato Hirotaka , Shimojo Masayuki , Yamabe-Mitarai Yoko
Published: March 2024

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.
Effect of Off-Stoichiometry on Elastic Modulus of TiC Phase in Mo-TiC Ternary System
Authors: Ida Shuntaro , Sekido Nobuaki , Yoshimi Kyosuke
Published: March 2024

MoSiBTiC alloy is a promising material for advanced aerospace applications and next generation high pressure turbine blades in jet engines and gas turbines. It mainly consists of Mo solid solution, TiC and Mo5SiB2 phases and has creep strength much stronger than Ni-base superalloys and better than SiC/SiC ceramic matrix composites. Furthermore, the fracture toughness of the alloy is much better (>15 MPa(m)1/2) than Mo-Si-B ternary alloys (<10 MPa(m)1/2) even if the volume fraction of Mo solid solution is less than 50 %. The improvement of fracture toughness would be caused not only by the continuity of Mo solid solution in solidification microstructure but also by TiC phase affecting as a fracture-resistant phase. In order to understand the microstructure evolution during solidification and the effect of TiC phase on the fracture toughness of the MoSiBTiC alloy, Mo-Ti-C ternary model alloys are dealt with in this study. Then, (1) liquidus surface projection and (2) isothermal section and the elastic moduli of TiC phase in equilibrium with Mo solid solution were focused on. The obtained liquidus surface projection suggests that the ternary transition peritectic reaction (L+ Mo2C->Mo+TiC) takes place in Mo-rich region. At 1800 °C, TiC phase in equilibrium with Mo phase contains at least 20.2 at% Mo and the Mo/TiC/Mo2C three phase region should exist around Mo-15Ti-10C.
Anisotropic Mechanical Properties of EBM Manufactured Alloy 718
Authors: Tanaka Yuta , Kubushiro Keiji
Published: March 2024

Alloy 718 is one of the most widely used for aircraft engine and gas turbine components requiring oxidation and corrosion resistance as well as strength at elevated temperatures. Alloy 718 has been produced in both wrought and cast forms, but metal injection molding and metal-based additive manufacturing (AM) technologies have the potential to create a three-dimensional component. Their mechanical properties are highly dependent on the types of powder processing, but the relationship between microstructures and properties has not been clarified. In this study, the mechanical properties of Alloy 718 manufactured by AM are compared to cast and wrought properties. The electron beam melting processed specimens with strong anisotropy showed higher yield strength, which can be explained by critical resolved shear stress. In addition, the creep deformation showed a complicated behavior which was different from that of wrought alloy. Such abnormal behavior was characterized by γ-channel dislocation activity.
Method of On-Site Repairing Steam Turbine Valve Seat with Laser Cladding
Authors: Liao Qiyin , He Xinxin , Zhang Gang , Cai Zhi
Published: March 2024

Steam turbine is one of the critical equipments in coal-fired power plants, steel P91 is a common material of its control valves. CoCr-based hardfacing on valve seats can resist long time exposure to water vapor with high temperature, thermal fatigue and solid particles erosion under high pressure. However, these hardfacing can crack and disbond during operation, which generates high risks for turbine systems and power plants. This article discussed the failure reasons of CoCr-based hardfacing, and introduced a method and practical experience of on-site repairing steam turbine valve seats with laser cladding NiCr coating.
Development of High Strength Mo Alloy (Mo-Mo5SiB2 Alloy) for Material Forming
Authors: Adachi Ippei , Watanabe Yuri , Nishino Nidenobu , Kadokura Takanori , Takida Tomohiro , Ikegaya Akihiko
Published: March 2024

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.
Establishing Induction Bending Technique for Ni-Based Alloy HR6W Large Piping
Authors: Nomura Kyohei , Kubushiro Keiji , Nakagawa Hirokatsu , Nishimoto Yuzo , Yamaguchi Takashi , Mihune Hideyuki
Published: March 2024

In order to establish a induction bending technique for Ni-based alloy HR6W large pipe, induction bending test was conducted on HR6W, which is a piping candidate material of 700°C class Advanced Ultra-Super Critical. In this study, a tensile bending test in which tensile strain was applied and a compression bending test in which compression strain was applied to the extrados side of the pipe bending part. As the results of these two types of induction bending tests, it was confirmed that a predetermined design shape could be satisfied in both bending tests. In addition, the wall thickness of the pipe was equal to or greater than that of the straight pipe section in compression bending. Therefore, if compression bending is used, it is considered unnecessary to consider the thinning amount of the bent portion in the design. Next, penetrant test(PT) on the outer surface of the bending pipes were also confirmed to be acceptable. Subsequently, metallographic samples were taken from the outer surface of the extrados side, neutral side and intrados side of the pipe bending portion. Metallographic observation confirmed that the microstructures were normal at all the three selected positions. After induction bending, the pipe was subjected to solution treatment. Thereafter, tensile tests and creep rupture tests were carried out on samples that were cut from the extrados side, neutral side and intrados side of the pipe bending portion. Tensile strength satisfied the minimum tensile strength indicated in the regulatory study for advanced thermal power plants report of Japan. Each creep rupture strength was the almost same regardless of the solution treatment conditions. From the above, it was possible to establish a induction bending technique for HR 6W large piping.
Creep Characteristics of Near Alpha-Ti Alloys and Proposal of Deformation Mechanism Map
Authors: Ito Tsutomu , Kitashima Tomonori , Yamabe-Mitarai Yoko
Published: March 2024

Titanium alloys are expected to be used as heat-resisting structural materials in the airplane and automotive industries. In this study, the creep properties of near-α Ti alloys consisting of a lamellar microstructure were studied. Ti–8.5wt%Al–8.0wt%Zr–2wt%Mo–1wt%Nb–0.15wt%Si alloy (alloy code, TKT34) and an alloy with 0.1 wt% of added boron (alloy code, TKT35) were used in this study. An ingot was hot forged at a temperature of 1,403 K and hot rolled (caliberrolling) at a temperature of 1,273 K to a reduction rate of approximately 90%. It then underwent solution treatment in a β single-phase region followed by air cooling. Finally, it was subjected to aging treatment for 28.3 ks at a temperature of 863 K and then air-cooled. Two solution treatment conditions were applied: a time of 1.8 ks at a temperature of 1,323 K (high temperature/short time (HS)) and a time of 3.6 ks at a temperature of 1,223 K (low temperature/long time (LL)). The average grain size of the prior β grains showed a tendency of the solution treatment temperature being low and the boron-added alloys tending to be small. The length and thickness of the lamellar of these alloys shortened or thinned owing to the addition of boron and at a low solution treatment temperature. The creep tests were carried out at an applied stress of 137 MPa and a temperature of 923 K in air. The creep rupture life of these alloys was excellent, in order of TKT35 (LL) < TKT34 (LL) < TKT35 (HS) ≦ TKT34 (HS). Therefore, the creep rupture life of these alloys was shown to be superior under the HS solution treatment condition as compared to the LL solution treatment condition. However, the minimum or steady-state strain rate of these alloys became slower in order of TKT 35 (LL)> TKT34 (LL)> TKT34 (HS) ≧ TKT35 (HS). The creep properties depended on the microstructure of the alloys.
Effect of Impurities in CO2 at Supercritical Pressure on Alloy Compatibility
Authors: Pint B. A. , Keiser J. R.
Published: March 2024

Direct-fired supercritical CO2 (sCO2) cycles are expected to result in sCO2 with higher impurity levels compared to indirect-fired cycles. Prior work at ambient pressure showed minimal effects of O2 and H2O additions, however, a new experimental rig has been built to have flowing controlled impurity levels at supercritical pressures at ≤800°C. Based on industry input, the first experiment was conducted at 750°C/300 bar in CO2+1%O2-0.25%H2O using 500-h cycles for up to 5,000 h. Compared to research grade sCO2, the results indicate faster reaction rates for Fe-based alloys like 310HN and smaller increases for Ni-based alloys like alloys 617B and 282. It is difficult to quantify the 310HN rate increase because of scale spallation. Characterization of the 5,000 h specimens indicated a thicker reaction product formed, which has not been observed in previous impurity studies at ambient pressure. These results suggest that more studies of impurity effects are needed at supercritical pressures including steels at lower temperatures.
Possibility of Scale Breakage by the Electromotive Force Generated in the Zirconium Oxide Scale at 873 K
Authors: Kawamura Kenichi , Kishimoto Gen
Published: March 2024

Oxide scale, whose ionic conductivity is larger than its electronic one, generate an electro-motive force between a metal/scale and a scale/gas interfaces. When the scale is thin, an electrical potential gradient is large. The large electrical potential gradient may have a possibility to break scales. To confirm the possibility, high temperature oxidation of zirconium on initial stage was observed by an acoustic emission (AE) technique. AE signal was detected before the scale thickness less than 3 μm. And an electrical response on sputtered zirconium oxide thin film was observed. When the applied voltage over 2.00 V, the electrical current was scattered.
Competitive Effect of Nb and V on High-Temperature Oxidation of α2-Ti-30Al Alloys
Authors: Jullian Domingo , Hayashi Shigenari , Takeyama Masao
Published: March 2024

The competitive effect of Nb and V additions on the high-temperature oxidation behavior of Ti- 30Al alloys were studied at 800°C in air. Oxidation performance increased with increasing Nb content, however, V additions eliminated the beneficial effect of Nb on oxidation performance, causing higher oxidation mass gains. In-situ high-temperature XRD by means of synchrotron source suggested dissolution of Nb5+ but lower valence of vanadium ions in the TiO2 oxide scale during oxidation. Dissolution of Nb and V ions with different valence in TiO2 during oxidation could cause the beneficial and detrimental effects observed on the performance of high-temperature oxidation of Ti-30Al.
Benchmarking Combined Cycle Power Plant Designs Employing 9-12%Cr CSEF Steels in Environments Prone to Steam Oxidation
Authors: Ceuca S. , Ferrara A. , Baietta S. , Campanari S. , Chiesa P. , Zecca Nicola
Published: March 2024

To stay competitive in today’s dynamic energy market, traditional thermal power plants must enhance efficiency, operate flexibly, and reduce greenhouse gas emissions. This creates challenges for material industries to provide solutions for harsh operating conditions and fluctuating loads. Higher efficiency demands steels with excellent steam oxidation resistance, favoring ferritic steels for cycling operation due to their limited thermal expansion. This paper presents a study modeling a combined cycle power plant using GE 9HA0.2 GT technology. The analysis compares different maximum live steam temperatures (585°C, 605°C, 620°C) and four alloys (grades 91 and 92, stainless S304H, and Thor 115) for heat exchangers exposed to steam oxidation. Results indicate that Thor 115, a creep strength enhanced ferritic (CSEF) steel, is a viable alternative to stainless steel for live steam temperatures above 600°C, offering improved oxidation resistance with minimal weight increase. Modern CSEF steels outperform stainless steel in power plants with lower capacity factors, reducing thermal fatigue during load changes. Increasing the live steam temperature boosts plant efficiency, leading to significant CO2 savings for the same power output.
Corrosion Behavior of Fe- and Ni-Base Alloys in High Temperature Carbon Dioxide Environment with Impurity Additions
Authors: Kim Sung Hwan , Cha Ji-Hwan , Subramanian Gokul Obulan , Jang Changheui
Published: March 2024

The effect of gas impurities on corrosion behavior of candidate Fe- and Ni-base alloys (SS 316LN, Alloy 800HT, Alloy 600) in high temperature CO2 environment was investigated in consideration of actual S-CO2 cycle applications. Preliminary testing in research and industrial grade S-CO2 at 600 °C (20 MPa) for 1000 h showed that oxidation rates were significantly reduced in industrial-grade S-CO2 environment. Meanwhile, controlled tests with individual impurity additions such as CH4, CO, and O2 in research-grade CO2 were performed. The results indicated that CH4 and CO additions did not seem to significantly affect oxidation rates. On the other hand, O2 addition resulted in lower weight gains for all alloys, suggesting that O2 may be primarily affecting corrosion behavior.
Resisting Attack by Hot CO2—A Comparison of Fe- and Ni-Base Alloys
Authors: Zhang Jianqiang , Young David J.
Published: March 2024

Model alloys of Fe-20Cr and Ni-20Cr (all compositions in weight %) and variants containing small amounts of Si or Mn were exposed to Ar-20CO2 and Ar-20CO2-H2O (volume %) at 650 or 700°C. Protective Cr2O3 scale was more readily formed on Fe-20Cr than Ni-20Cr, as a result of the different alloy diffusion coefficients. Silicon additions slowed chromia scale growth, promoting passivation of both alloy types. Water vapour accelerated chromia scaling, but slowed NiO growth.
Nickel Chromium Alloy Claddings for Extension of Fossil-Fueled Boiler Tubing Life
Authors: Baker Brian A. , Kiser Samuel D.
Published: March 2024

The INCONEL filler metals 72 and 72M have been utilized significantly for weld overlay protection of superheaters and reheaters, offering enhanced corrosion and erosion resistance in this service. Laboratory data conducted under simulated low-NOx combustion conditions, field exposure experience, and laboratory analysis (microstructure, chemical composition, overlay thickness measurements, micro-hardness) of field-exposed samples indicate that these overlay materials are also attractive options as protective overlays for water wall tubes in low-NOx boilers. Data and field observations will be compared for INCONEL filler metals 72, 72M, 625 and 622.
Evaluation of Weld Cracking Susceptibility of Candidate Ni-Based Alloys for Advanced USC Boilers
Authors: Saito Nobuhiko , Komai Nobuyoshi , Hashimoto Keita , Kitamura Masaki
Published: March 2024

The susceptibilities of hot cracking and reheat cracking of A-USC candidate Ni-based alloys were evaluated relatively by Trans-Varestraint testing and Slow Strain Rate Tensile (SSRT) testing. In addition, semi-quantitative evaluation of the stress relaxation cracking susceptibility of Alloy 617 was conducted, because stress relaxation cracking in the heat affected zone (HAZ) has actually been reported for repair welds in Alloy 617 steam piping in European A-USC field-testing. Solidification cracking susceptibilities of Alloy 617 were the highest; followed by HR35, Alloy 740 and Alloy 141, which were all high; and then by HR6W and Alloy 263, which were relatively low. In addition, liquation cracking was observed in the HAZ of Alloy 617. The reheat cracking susceptibilities of Alloy 617, Alloy 263, Alloy 740 and Alloy 141 were somewhat higher than those of HR6W and HR35 which have good creep ductility due to the absence of γ’ phase precipitates. A method to evaluate stress relaxation cracking susceptibility was developed by applying a three-point bending test using a specimen with a V-notch and finite element analysis (FEA), and it was shown that stress relaxation cracking of aged Alloy 617 can be experimentally replicated. It was proposed that a larger magnitude of creep strain occurs via stress relaxation during the three-point bending test due to a higher yield strength caused by γ’ phase strengthening, and that low ductility due to grain boundary carbides promoted stress relaxation cracking. The critical creep strain curve of cracking can be created by means of the relationship between the initial strain and the creep strain during the three-point bending tests, which were calculated by FEA. Therefore, the critical conditions to cause cracking could be estimated from the stress relaxation cracking boundary from of the relationship between the initial strain and the creep strain during the three-point bending test.
Study on GTAW Welded Joint of Nimonic 263 Alloy after Aging at 750℃ for Gas Turbine Transition Pieces
Authors: Jianshui Ye , Lei Liu , Yuming Ding , Renjie Yang
Published: March 2024

Nimonic 263 alloy was selected for gas turbine combustor transition piece due to its excellent high temperature mechanical performance. In present work, Nimonic 263 alloy plate with thickness of 5mm was welded using 263 filler metal by GTAW, then post weld heat treatment of 800℃/8h/air cool was carried out. The hardness and impact toughness of welded joints were measured, and the microstructure evolution after aging at 750℃ for 3000h was investigated by scanning electron microscopy(SEM). The results show that, during the aging process, the hardness of weld metal increases firstly and then decreases. The impact toughness decreases significantly at first and then increase. Furthermore, some fluctuations can be detected in hardness and impact toughness after long-term thermal exposure. The significant decrease in the impact toughness of the aged welded joints mainly results from the precipitation of η phase around grain boundary and intergranular MC phase. The hardness of weld metal increases due to the precipitation of more carbides and γ′ phase after 1000h aging, then decreases owing to the growth of γ′ phase after 3000h aging.
The Improvement of Repair Welding for CrMoV Turbine Casings
Authors: Nakade Katsuyuki , Tokoro Masaaki , Lolla Tapasvi , Bridges Alex , Siefert John
Published: March 2024

CrMoV cast steels are widely utilized for steam turbine and valve casings, and are subjected to operating and loading conditions which can promote damage mechanisms such as thermal fatigue, creep, erosion, etc. These components are subjected to variable, and sometimes severe conditions because of flexible operation. Therefore, there is a growing need for weld repair techniques including those which do not mandate post weld heat treatment (PWHT), e.g. so-called ‘temper bead’ weld repair. In this study, a simulated weld repair was performed using a temper bead technique. The maximum hardness in the heat affected zone (HAZ) CrMoV steel was ≤400HV. The integrity of the repair methodology was investigated using destructive testing, including hardness mapping, Charpy impact tests, tensile tests, low cycle fatigue and cross-weld creep, and the microstructure was assessed using light optical microscopy and scanning electron microscopy (SEM).
Investigation of the Stress Relief Cracking Behavior of Welded 25% Chromium Stainless Steel Tubes
Authors: Unterumsberger Fabian , Bernds Dietrich
Published: March 2024

In a European ultra-supercritical (USC) power station repaired reheater bundle tubes made out of 25% Chromium stainless steels developed stress relief damages at the tube-to-tube butt welds, leading to leakages after only 8.500 hours of operation. Laboratory investigations of the leakages revealed common features of stress relief cracking (SRC) such as highly localized intergranular cracking in the heat affected zone (HAZ) near the fusion line, creep void formation at the crack tip and around the crack. At that time no other SRC damages were known for the employed 25% Chromium stainless steel boiler tubes. This article briefly describes the SRC damage found on the repaired reheater bundle tubes. It further provides insight on the several laboratory tests employed to assess the SRC behavior of welded joints of different creep resistant stainless steels. Among the selected test methods were Slow-Strain-Rate-Tests (SSRT), static 3-point bending tests derived from the Van Wortel approach and component tests. The results provided by the described tests methods have shown that the SRC behavior of a given material combination must be assessed by different techniques. This is especially the case for the evaluation of potential countermeasures and for the determination of the service conditions leading to the highest susceptibility.
Microstructure Characterization of a 2.25Cr-1Mo Main Steam Pipe Weldment after Long-Term Service
Authors: Yang Bin , Li Ming-Chao , Jiang Wen-Chun , Wang Ming-Lei , Song Ming-Da , Zhao Yan-Ling
Published: March 2024

Metallographic tests, micro-hardness tests, mechanics performance tests and Energy Dispersion Spectrum (EDS) were conducted for a 2.25Cr-1Mo main steam pipe weldment served for more than 32 years. Microstructural evolution of the 2.25Cr-1Mo base metal and weld metal was investigated. Degradation in micro-hardness and tensile properties were also studied. In addition, the tensile properties of subzones in the ex-service weldment were characterized by using miniature specimens. The results show that obvious microstructural changes including carbide coarsening, increasing inter lamella spacing and grain boundary precipitates occurred after long-term service. Degradation in micro-hardness is not obvious. However, the effects of long term service on tensile deformation behavior, ultimate tensile strength and yield stress are remarkable. Based on the yield stress of micro-specimens, the order of different subzones is: WM>HAZ>BM, which is consistent with the order of different subzones based on micro-hardness. However, the ultimate tensile strength and fracture strain of HAZ are lower than BM.
Characterization of Suitable Fillers for Butt Weld of Creep Aged X20 and Virgin P91 Pipes
Authors: Mphaphathi Thendo , Maledi Nthabiseng , Bezuidenhout Marthinus , Pete Thobeka , Westraadt Johan , Dreyer Bernard
Published: March 2024

Components such as tubes, pipes and headers used in power generation plants are operated in a creep regime and have a finite life. During partial replacement, creep exhausted materials are often welded to virgin materials with superior properties. The aim of this study was to identify a suitable weld filler material to join creep aged X20CrMoV12-1 to a virgin P91 (X10CrMoVNbV9-1) steel. Two dissimilar joints were welded using the gas tungsten arc welding (GTAW) process for the root passes, and manual metal arc (MMA) welding for filling and capping. The X20 and the P91 fillers were selected for joining the pipes. The samples were further heat treated at 755°C to stress relief the samples. Microstructural evolution and mechanical properties of the weld metals were evaluated. The average hardness of X20 weld metal (264 HV10) was higher than the hardness measurement of P91 weld metal (206 HV10). The difference in hardness was attributed to the high carbon content in X20 material. The characterisation results revealed that the use of either X20 or P91 weld filler for a butt weld of creep aged X20 and virgin P91 pipes material does not have a distinct effect on the creep life and creep crack propagation mechanism. Both weld fillers (X20 and P91) are deemed to be suitable because limited interdiffusion (<10 μm) of chromium and carbon at the dissimilar weld interface was observed across the fusion line. The presence of a carbon ‘denuded’ zone was limited to <10 μm in width, based on the results from local measurements of the precipitate phase fractions using image analysis and from elemental analysis using EDS. However the nanoindentation hardness measurements across the fusion line could not detect any ‘soft’ zone at the dissimilar weld interface. The effect of the minute denuded zone was also not evident when the samples were subjected to nanoindentation hardness testing, tensile mechanical testing, Small Punch Creep Test (SPCT) and cross weld uniaxial creep testing.