The cast microstructure of 1st generation MoSiBTiC alloy composed of Mo solid solution (Mo ss ), Mo 5 SiB 2 , TiC phases largely affects tensile-creep behavior in the ultrahigh temperature region. Mo 5 SiB 2 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 Mo 5 SiB 2 has a strong texture while Moss and TiC show randomly-oriented distribution in a cast ingot. During creep, Mo 5 SiB 2 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 Mo 5 SiB 2 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.

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.

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 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.

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 Mo 5 SiB 2 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+ Mo 2 C->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/Mo 2 C three phase region should exist around Mo-15Ti-10C.

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.

Advanced martensitic 9% chromium steels have been identified as the most favored group of materials for high temperature applications in thermal power plants. To extend the temperature range of martensitic steels up to 650°C large effort was put on the development of new alloy concepts. The so-called MARBN concept (Martensitic steel with defined Boron/Nitrogen relation) provides increased creep rupture strength due to higher solid solution strengthening and improved microstructural stability. The major improvement is the reduction of type IV cracking in welded joints, which shifts the focus to the creep rupture strength of the weld metal. This paper illustrates the process experience of the steel foundry for production of heavy cast components in latest state of the art 9-12%Cr-MoCoVNbNB-alloyed cast steel grades and the newest state of development and prototype components in MARBN cast steel grades. Metallurgy, solidification, heat treatment and welding are main items to be considered for development of new, complex steel grades for foundry processing with the help of empiric processing in test programs and thermo-physical simulation. As welding is an essential processing step in the production of heavy steel cast components a good out-of-position weldability is required. Moreover a stress-relieve heat-treatment takes place subsequently after welding for several hours. This contribution also deals with the development of matching welding consumables for the production of heavy cast components and discusses the challenges of defining appropriate welding and heat treatment parameters to meet the requirements of sufficient strength and toughness at ambient temperature. Additionally, first results of creep rupture tests are presented.

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.

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.

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.

The Alloys-by-Design approach, involving large-scale CALPHAD calculations to search a compositional range, has been used to isolate a suitable nickel-based superalloy for additive manufacturing (AM) by optimizing the trade-off between processability and increasing strength. This has been done in response to the limited focus on development of new superalloys designed to overcome the limitations of the AM process, specifically the high defect density of parts made from high-performance alloys. Selected compositions have been made using gas atomization, and laser powder-bed fusion AM trials were performed. The resulting properties were evaluated in the as-processed, heat treated and thermally exposed conditions. The assessment, combined with characterization techniques including scanning electron microscopy and atom probe tomography, rationalizes a temperature capability up to and above 850 °C, and demonstrate the opportunity to develop alloys with properties beyond the current state of the art.

In the context of research of lighter and/or stronger high temperature materials in order to improve aeroengines, the present work shows an example of a powder metallurgy (PM) manufacturing route for TiAl alloys that could be used for low pressure turbine (LPT) blades processing. In this frame, two different alloys, Ti-47Al-1Fe-1Zr-1Mo-0.2Si (at. %) FZM and Ti- 43.5A1-4Nb-1Mo-0.1B (at.%) TNM-B1, were gas-atomized into powders, extruded, heat-treated and mechanically tested.

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

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.

So-called Ni base dual two-phase intermetallic alloys are composed of primary Ni 3 Al (L1 2 ) phase precipitates among eutectoid microstructures consisting of the Ni 3 Al and Ni 3 V (D0 22 ) phases. In this article, microstructural refinement of an alloy with a nominal composition of Ni 75 Al 10 V 15 (in at.%) was attempted by various heat treatment processes. When the alloy was continuously cooled down after solution treatment, fine and cuboidal Ni 3 Al precipitates were developed by rapid cooling while coarse, rounded and coalesced Ni 3 Al precipitates were developed by slow cooling. When the alloy was isothermally annealed at temperatures above the eutectoid temperature, the morphology of the Ni 3 Al precipitates changed from fine and cuboidal one to large and rounded one with increase in annealing time. When the alloy was annealed at temperatures below the eutectoid temperature, the Ni 3 Al precipitates were grown keeping cuboidal morphology. The morphological change from the cuboidal to rounded Ni 3 Al precipitates was induced by the transition from the growth driven by elastic interaction energy between the precipitate and matrix to that by the surface energy of the precipitate. Fine and cuboidal Ni 3 Al precipitates generally resulted in high hardness.