bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 &lt;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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 (&gt;15 MPa(m)1/2) than Mo-Si-B ternary alloys (&lt;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-&gt;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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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) &lt; TKT34 (LL) &lt; 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)&gt; TKT34 (LL)&gt; 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

Abstract
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

Abstract
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

Abstract
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.