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A strong temperature-dependent effect in the range from 25°C to 700°C in the nanomechanical behaviour has been found in a single-crystal nickel-base superalloy. The hardness of this alloy gradually...

By performing solution treatment at various temperatures, creep property measurements, and microstructural observations, the influence of the solution temperature on the microstructure uniformity a...

The focus of this study is on assessing the chromium-depletion occurring in the subsurface layer associated with the formation of chromium oxide upon high-temperature exposure. As this is a critica...

This work presents the experimental data obtained using an integrated approach in the study of the chemical, crystallographic and morphological homogeneity of the structure of a heat-resistant material on a nickel base with carbide-intermetallic hardening and an increased content of the γ-phase, synthesized on single-crystal substrates of various compositions with CHO in Z-direction. Using the proposed method for studying the capabilities and certification of different-level structural structures of samples in the initial state and after thermal study of the impact. The analysis was carried out using the system for EBSD analysis integrated into the scanning electron microscope and the software package for the analysis of electron microscopic images.

The evolution of microporosity in single-crystal nickel-base superalloy CMSX-4 during hot isostatic pressing has been investigated by high resolution tomography at the European Synchrotron Radiation Facility in Grenoble. The kinetic dependencies of microporosity annihilation in the superalloy in initially as-cast and homogenized conditions were obtained. It was shown that smaller homogenization pores of about 5-10 μm in size are rapidly annihilate during hot isostatic pressing, while annihilation of larger solidification pores of size up to a few hundred micrometer takes a long time. After commercial hot isostatic pressing at 1288 °C, 103 MPa, 4 h only rare pores smaller than 20 μm remain, which are not critical for fatigue strength.

The relationship between the long-term strength and the structural-phase and physico-chemical parameters of castable polycrystalline nickel-based superalloys is considered. A regression model for prediction of the durability at a temperature of 1100 °C and a stress of 80 MPa of the considered class of alloys is proposed. The model takes into account the amount of the γ'-phase, the γ'-solvus and solidus temperatures, γ/γ'-misfit, the lattice spacing of the γ- and γ'-phases, and the atomic mass of the alloy. The reliability of the durability prediction is confirmed by comparison with the experimental results on the long-term strength at temperatures 1000, 1050 and 1100 °C of a number of industrial and experimental castable polycrystalline nickel-based superalloys.

Microstructural evolution of a nickel-base single-crystal superalloy during homogenisation at ultra-high temperature has been investigated using scanning electron microscope and electron probe micr...

Cooling-induced precipitation of the strengthening γ’ phase is commonly investigated in Ni-base superalloys with a high γ’ volume fraction, where it is used to control the final microstructure and ...

Nickel-based superalloy GH4169 has high strength and stability at high temperature and is widely used in aerospace and military fields.However, due to the problems of hard spots and poor thermal conductivity in actual processing,it is difficult for workers to select reasonable processing parameters during processing,which increases the difficulty of processing.In order to optimize the milling parameters,reduce the milling cost and operational difficulties in actual machining,we used ABAQUS finite element analysis software to simulate the 3D milling of GH4169 nickel base superalloy.The variation of milling force during milling was studied.The influences of milling speed,feed per tooth and radial depth on milling force were analyzed and the results of the simulation were compared with those obtained by orthogonal experiment.The variation of milling force was verified.Finally,we obtained the reasonable milling parameters.

Nickel base single crystal superalloy is widely used in hot end parts of aeroengine because of its excellent creep, fatigue and oxidation resistance. In the face of strong market demand and the emergence of new technologies and methods, in 2019, nickel-based single crystal superalloys have made remarkable achievements in preparation and heat treatment processes, repair techniques, test methods, characterization methods, theoretical simulation analysis and composition design, which continuously promotes the development of nickel base single crystal superalloy to the direction of high performance and low cost. The present work reviews the progresses from preparation and heat treatment process, repair technology of service alloy structure, service evaluation of alloy, high flux composition design. The progress in the design, preparation and engineering application of superalloy materials will eventually promote the development of a new generation of aeroengine.

Two-step solution cooling experiment was performed to investigate the precipitation behavior in a polycrystalline nickel base superalloy. Both experimental and simulation results show that the particle size distribution (PSD) of γ′ precipitates strongly depends on the transition temperature (Ttrans) that is closely related to their nucleation driving force. We proposed a modified model that considers multi-modal PSD to predict the yield strength, which is numerically validated by the experimentally measured hardness.

Under conditions of multilayer microplasma powder overlay welding process of nickel-base difficult to weld high temperature strength alloys with a content of the strengthening γ׳- phase more than 50 vol. % the tendency to the reheating cracks formation in the corresponding welded joint "cast-deposited metal" from is largely determined by the structure and properties of the deposited metal. With appropriate research studies of the crack formation tendency, it was proposed not to post factum quantitatively evaluate its manifestations by the number and length of cracks, but to focus on studies of the preliminary resistance stage to their formation in the overlay metal. It is shown that an objective method for the deformation ability studying can be tensile testing at elevated temperatures (1000 ° C) of overlay metal samples. This allows us to move from the two-dimensional system of its assessment “temperature T - critical strain ε” when using a common machine test according to the international standard for hot crack testing resistance ISO 17641: 2005 to the three-dimensional system “temperature T - critical stress σ (Rmcr ) - critical deformation ε (Acr)”. For the overlay metal ZhS32 obtained by the microplasma powder overlay welding process, in the state immediately after deposition, the limited deformation capacity at 1000 °C was established: Rmcr ~ 345 МРа (tensile strength); Acr ~ 0,1 % (percentage elongation). Based on the previously established limited deformation ability of the ZhS6K overlay metal in the after deposition state, it is proposed to use the quantitative criterion ε 1000°C (А1000°C) for predictive assessments of the possibility of ensuring the technological strength of the overlay metal of nickel-base difficult to weld high temperature strength alloys. The reduced level of mechanical properties of the overlay metal ZhS32 after its crystallization in the welding pool is associated to the some its primary structure features. Using scanning electron microscopy, the following differences were established in comparison with a similar cast metal of the ZhS32 alloy: dendritic cell cross section; dispersion and uniform distribution of the carbide phase particles; the visual signs absence of the release of strengthening γ׳-phase particles on the dendrite axes. It is shown that the presence of dispersed hardening in the structure of nickel-base high temperature strength alloys of the ZhS32 and ZhS6 types depends on the cooling rate of the molten metal during crystallization, and in the case of the overlay metal it is finally formed only during subsequent heat treatments in the range of aging-homogenization modes.

A systematic study on the wettability and interactions between superalloy melts with various Re contents and Al2O3-based ceramic moulds was presented in this paper. It was found that the increase of Re content inhibited the interfacial reactions to some extent. With regard to the 0, 1.5 and 3Re alloys, a double reaction layer containing Al2O3 and HfO2 was formed at the interface, but the thickness of reaction layer decreased with the increase of Re content. However, only Al2O3 phase was detected at the interface when the content of Re was 6 wt%, and the interface reaction was the weakest and the thickness of reaction layer was the thinnest. The wetting angle of the alloy/ceramic system increased as the level of Re increased. Moreover, the formation of viscous sand at the interface mainly depended on the change of wetting angle of the system.

All engineering materials have the potential to contain inhomogeneities that can act as initiators for fatigue cracks during cyclic loading. One class of inhomogeneity that can occur as a result of the processes used to create metallic materials is a ceramic inclusion, typically resulting from the raw material contamination during the melting process. This article examines the predicted behavior of hard ceramic inclusions in a nickel-base superalloy metallic matrix. Compressive residual stresses are created in the inclusion during cool down from a stress-free state at high temperature. The influence of the proximity of the inclusion to the surface of the matrix material is examined, together with the impact of subsequent uniaxial loading on the stress field in the inclusion and in the surrounding material. The stress field in the ceramic inclusion is observed to transition from compressive to tensile as a function of the proximity of the inclusion to the surface of the material and the applied uniaxial stress field. For deep subsurface inclusions, the uniaxial stress field required to achieve a tensile stress in the inclusion is close to the yield stress of the material. The sensitivity of this critical stress to material cyclic hardening behavior and to the temperature difference between the stress-free state and the operating state is also explored. The significance of these modeling results is discussed in terms of the sensitivity of nickel-base superalloys to crack formation and growth from ceramic inclusions and hence the impact on probabilistic fatigue life assessments of the presence, location and size of the ceramic inclusions.

Four kinds of single-crystal Ni-base superalloys (12Ta–7.5Cr–5Co–4.8Al–1.9Mo–1Ti, balance Ni in wt%) containing (0–3) wt%W and (1–4) wt%Re were cast, and oxidized at 1000 °C for up to 275 h in air. In the as-cast condition, the microsegregations of (Cr, Co, Mo, W, Re) in the dendrites and (Al, Ti, Ta) in the interdendritic regions were observed. The γ/γ′ eutectic phases formed in the interdendritic regions. The oxidation rate of the cast alloys was comparable to that of the 2nd generation alloys, displaying relatively good oxidation resistance due primarily to the formation of stable alumina and chromia on the surface. Especially, the alloy with 2 wt% W and 2 wt% Re showed the best oxidation resistance among the four alloys. Uniform oxidation occurred in the dendrite area, whereas nodular oxidation occurred in the interdendrite region.

After presenting the state-of-the-art Bridgman casting process to obtain single crystalline components, as well as alternative directional solidification techniques, common processing defects (recrystallized grains, freckles, microsegregation, slivers, etc.) are reviewed and their formation mechanisms are discussed. The typical heat treatment sequence applied to Ni-base single crystal superalloy (when needed) is then detailed from both microstructure and mechanical properties points of view. Creep properties of these alloys are shown to be mainly dependent on the heat treatments following investment casting, especially the solution heat treatment. Conversely, fatigue properties are mainly controlled by the solidification processes, through the casting pore size and spatial distribution, when oxidation has no major contribution to the crack initiation mechanisms.

The relation between Ta/W ratio and mechanism of γ/γ’ eutectics morphological changes and solidification path was investigated for experimental nickel-base superalloys. Thermal analysis and...

Density functional theory was used to investigate the anticorrosion mechanism of Cr-doped nickel-base alloy in Br/O environment. The adsorption properties including adsorption energy, bond length a...

Superdislocation configurations in a [011]-oriented single crystal superalloy after creep at 1100 °C/150 MPa have been investigated. Besides a〈110〉 superdislocations, a[100] superdislocations are observed. TEM analysis shows that these a[100] superdislocations are pure edge dislocations and mainly lie on (100) plane with 〈011〉 directions. They form by the reactions of two matrix dislocations with different Burgers vectors, and they may move in a similar way to a〈100〉 dislocations in [001] specimens owing to the zero Schmid factors.

Components of gas turbines must be extremely resistant to high temperatures, high stresses, high-temperature corrosion, and erosive environments. The materials used in these environmental conditions are mainly nickel-based superalloys. In this study, the low-cycle fatigue of the nickel-based superalloy Inconel 792 was examined. The total strain range of a gas turbine between 760 °C and 870 °C was considered as the parameter representing the actual gas turbine operation. In addition, tests were performed using a trapezoidal waveform of the total strain to reflect the operation-stop conditions of a gas turbine with frequent shutdowns. The results of the fatigue test were compared with the Coffin–Manson method and energy method. The fractured surface was analyzed using a scanning electron microscope (SEM).

The high temperature low cycle fatigue behavior of specimens manufactured from a single crystalline nickel base superalloy processed by selective electron beam melting (SEBM) has been investigated with respect to the effect of different heat treatments. The fatigue lifetime of heat treated material was significantly higher than that of as-built material. Applying hot isostatic pressing (HIP) with an integrated heat treatment resulted in even longer fatigue life. Lifetime limiting crack initiation occurred at interfaces of melting layers, at micro-porosity generated during solidification or, in HIP treated samples, at precipitates which formed at the location of collapsed pores.

A newly developed heavily alloyed polycrystalline nickel-base superalloy containing rhenium and intended as a structural material for turbine discs in gas turbine engines has been studied. Homogeni...

Cored wires are used in numerous welding processes with or without extern al gas or flux shielding. Submerged are welding (SAW) with eored wires, seamed or seamless, for joining mild and low alloyed steel grades is a technique that has demonstrated clear advantages during the three last decades. Ever since its invention, the SAW process has evolved with one main goal: to combine quality with produetivity. With low alloy wires, the benefits have already been clearly demonstrated and widely exploited. However, little has been written on SA Wand cladding with eored wires for eorrosion or he at resisting applieations. Its extension to high alloy eompositions brings eorresponding benefits and adds so me specific and unique features. This paper foeuses on consumable specificities and on the quality and productivity features of SAW with CRA (corrosion resistant alloy) cored wires. It deseribes the potential as weIl as the limitations ofthis technique. Cored wires are now used for submerged are welding of almost aIl stainless steels ranging from soft martensitic to super-duplex, and for aseries of nickel base compositions as weIl as for cladding cobalt base aIloys. Examples of industrial applications with austenitic, duplex, martensitic and heat resisting stainless steels are given to illustrate the potential ofthe eored wire solution.

In recent years, the micro-deformation mechanisms of the tension/compression behavior for nickel-base single-crystal superalloys have been studied extensively and general agreements have been derived. Based on these researches, a new model called united tension/compression asymmetry micro-mechanical model (UTCAM) has been proposed, which can effectively estimate the initial yield strength of nickel-base single-crystal (SC) superalloys under different loading directions. Considering the combined effects of octahedral slip system and cubic slip system, slip control factor is introduced in the UTCAM to determine the type of the open slip system of nickel-base single-crystal superalloys during deformation, thus making this model cover a rather wide range of application. Furthermore, the UTCAM is applied to hot tension and compression tests of three typical nickel-base SC superalloys (PWA1480-593 °C, RENE N4-760 °C and DD407-760 °C). The predicted initial yield strengths of the nickel-base SC superalloys are in good agreement with the experimental results, and the UTCAM proves to be effective.

In order to improve the composition and microstructure of nickel-base single crystal superalloys, equilibrium phases of third generation single crystal superalloys RenéN6 and CMSX-10 have been researched by using thermodynamic calculation software JMatPro. The calculated results indicated that the two superalloys have the same equilibrium phases, such as liquid phase, γ phase, γ’ phase and TCP (topologically close-packed phases), however, there are differences in the quantity and temperature range. RenéN6 alloy has higher content of μ phase. And CMSX-10 alloy has higher γ’ phase precipitation temperature and more γ’ phase precipitates.

This research has an aim to evaluate the effect of temperature dropping conditions during solution treatment of reheat treatment process on final restored microstructure of cast nickel base superalloy, grade MGA-1400, a gas turbine blades materials, which had been degraded under long-term service at high temperatures and pressure. Generally, reheat treatment process to restore the degraded microstructure of the alloy consists of solution treatment of 1100-1125°C for 4 hours and precipitation aging of 845-865°C for 24 hours. However, the temperature dropping could be practically occurred due to the machine error of high temperature vacuum furnace. Therefore, the research had simulated various conditions of temperature dropping during solution treatment at temperature of 1100°C and 1125°C with decreasing temperature to 845°C after a) solutioning for 1 hours b) solutioning for 2 hours and c) solutioning for 3 hours then temperature was increased again to the required 1100°C and 1125°C. Then all various solution treated specimens were performed with precipitation aging at temperature of 845°C and/or 865°C for 24 hours. From all obtained results, it was found that the effect of temperature dropping provided the different in received reheat treated microstructures when considering in term of precipitation gamma prime particle morphology such as shape, size and phase density.

Optimizing hot workability and processing parameters of the difficult-to-work powder metallurgy (P/M) superalloy is critical to obtain a desired component through thermo-mechanic processing (TMP). In this study, a P/M superalloy with tailored grain structure and γ′ particle was prepared through atomization and hot isostatic pressing, then thermal compression tests were performed to evaluate its hot workability based on processing maps and microstructure evolution. Considering the friction and temperature variations during deformation, the flow data were corrected via an integrated method, to construct dependable processing maps. The results illustrated that the P/M superalloy prepared by the modified processing method presents superior hot workability, comparing with the P/M superalloys produced by different routes.

In order to determine the safe operational life of the components of gas turbine engines (GTE), introductory tests of nickel-base heat-resistant alloys (NHRA) have been performed. X-ray fluorescence and X-ray diffraction analyzes, optical microscopy and Vickers hardness measurements provided data on the phase-structural state and mechanical properties of the pristine ZhS6K-VI and ZhS32-VI alloys obtained by equilibrium and high-speed directional crystallization, respectively. Almost complete compliance of the investigated materials with the certified alloys in chemical and phase composition has been found. A significant difference in the parameters of the fragments of the microstructure of the investigated alloys, which is naturally consistent with the conditions of equilibrium and high-speed directional crystallizations, was revealed. A slightly lower anisotropy of microhardness (2.8 %), measured in transverse and longitudinal sections, was found in the ZhS6K-VI alloy as compared to the anisotropy (5.1 %) in the ZhS32-VI alloy. The obtained results will be used to test a non-destructive method for determining the safe operational life of gas turbine engine components.

The cast nickel-base MAR-M247 superalloy has been widely used for high-temperature components. In this work, the creep behaviour of two alternates of MAR-M247 superalloy with different grain size processed at different temperatures of casting are compared. Under the creep testing conditions used in this study, only negligible differences of creep behaviour of the alternate alloys were found and the evaluated creep characteristics correspond to the power-law or dislocation creep. The microstructure of the alloys consists of a 𝛾 matrix with a eutectic, 𝛾' strengthening cubic precipitates, and M6C and M23C6 carbides. Increasing the temperature induces the dissolution of some M23C6 carbides. Fractures of both variants of alloys exhibit a more ductile character at higher temperatures, while at lower temperature a mixture of brittle and ductile fracture modes was observed, which changes the creep fracture ductility.