High-temperature Alloys Research Articles

Electrochemical cutting with flexible electrode of controlled online deformation

Abstract Improvements in aero-engine performance have made the structures of the aero-engine components increasingly complex. To better adapt to the processing requirements of narrow twisted channels such as an integral shrouded blisk, this study proposes an innovative method of electrochemical cutting in which a flexible tube electrode is controlled by online deformation during processing. In this study, the processing principle of electrochemical cutting with a flexible electrode for controlled online deformation (FECC) was revealed for the first time. The online deformation process of flexible electrodes and the machining process of profiles were analysed in depth, and the corresponding theoretical models were established. Conventional electrochemical machining (ECM) is a multi-physical field-coupled process involving electric and flow fields. In FECC, classical mechanics are introduced into the tool cathode, which must be loaded at all times during the machining process. Therefore, in this study, before and after the deformation of the flexible electrode, a corresponding simulation study was conducted to understand the influence of the online deformation of the flexible electrode on the flow and electric fields. The feasibility of flexible electrodes for online deformation and the validity of the theoretical model were verified by deformation measurements and in situ observation experiments. Finally, the method was successfully applied to the machining of nickel-based high-temperature alloys, and different specifications of flexible electrodes were used to complete the machining of the corresponding complex profiles, thereby verifying the feasibility and versatility of the method. The method proposed in this study breaks the tradition of using a non-deformable cathode for ECM and adopts a flexible electrode that can be deformed during the machining process as the tool cathode, which improves machining flexibility and provides a valuable reference to promote the ECM of complex profiles.

Study on properties of pre-alloy powder of TiNiHf high temperature shape memory alloy for additive manufacturing by preheating treatment

In this work, pre-alloyed powder high-temperature shape memory alloy (Ti30Ni50Hf20) for additive manufacturing was preheated at 300–800°C and thermoscycled at 650°C to examine the influence of preheating temperature and thermal cycle number on the phase composition and phase transformation behavior. The results showed that the H phase precipitation occurred in the matrix with the rising preheating temperature within 300–600°C, and the phase transformation temperature of the pre-alloyed powders also increased. When the preheating temperature exceeded 600°C, the H phase dissolved back into the matrix, and the phase transformation temperature decreased. A total of 50 thermal cycles were conducted on the pre-alloyed powders at 650°C, and the phase transformation temperature and phase composition remained stable after cycling. It can be concluded that the preheating temperature greatly affected the phase composition and phase transformation behavior of Ti30Ni50Hf20 high-temperature shape memory alloy pre-alloyed powders, while the number of thermal cycles delivered a minor effect.

Advanced corrosion-resistant materials for enhanced nuclear fuel performance: A conceptual review of innovations in fuel cladding against molten salt degradation

The increasing demand for efficient and sustainable nuclear power has led to the development of advanced corrosion-resistant materials that can significantly enhance nuclear fuel performance. This conceptual review focuses on the innovations in fuel cladding materials designed to resist degradation in molten salt environments, which are crucial for advanced nuclear reactors like molten salt reactors (MSRs). Fuel cladding serves as a critical barrier between the nuclear fuel and the reactor environment, and its ability to withstand extreme temperatures and corrosive conditions is essential for safe and efficient reactor operation. Recent advancements in materials science have introduced novel alloys and coatings that demonstrate superior corrosion resistance in molten salts, which are used as both coolants and fuel solvents in MSRs. These innovations include high-temperature nickel-based alloys, refractory metals, and ceramic coatings, which are engineered to reduce the effects of molten salt corrosion, such as oxidation, pitting, and embrittlement. By enhancing the durability of fuel cladding, these materials contribute to improved fuel performance, longer reactor lifespans, and increased safety. This review explores key developments in corrosion-resistant materials, emphasizing the mechanisms by which these materials mitigate molten salt degradation. Additionally, it highlights the challenges associated with material selection, fabrication, and long-term performance in the highly corrosive environments of advanced nuclear reactors. Ongoing research into these materials offers promising avenues for the future of nuclear energy, particularly in addressing the limitations of current fuel cladding technologies. In conclusion, the use of advanced corrosion-resistant materials represents a significant step toward enhancing the performance and safety of nuclear fuel, ensuring the viability of MSRs and other advanced reactor designs. Continued innovation in this field is essential for the future of nuclear power.

Molecular dynamics simulation of gradient alloying distribution on the nano-mechanical properties of Nb-Zr alloys

Abstract In this work, a nano-indentation process of homogeneous Nb-Zr alloy and gradient Nb-Zr alloy was simulated using molecular dynamics simulation. The effects of Zr content, system temperature, indentation radius on the mechanical properties and micro-deformation were investigated. Comparing the homogeneous and gradient alloys, it was revealed that the gradient alloy had a smoother mechanical performance. The results showed that the effect of Zr content on the hardness of Nb-Zr homogeneous alloy was not linear. The hardness rose followed by a decline with increasing Zr content and the turning point came at 1.5 wt.%. Under high temperatures, the Nb-Zr homogeneous alloy and gradient alloy layer retained extremely high hardness, exhibiting excellent mechanical properties. Due to the entanglement of multiple dislocations in gradient Nb-Zr alloy at high temperatures, the hardness still increased with increasing temperature at high temperatures. The influence of indentation size on nano-indentation experiments was mainly affected by the curvature of the indented part. It was worth noting that gradient alloys could disperse stress faster and reach a stable state during the loading process. The hardness of the Nb-Zr homogeneous alloy layer first increased and then decreased as the Zr content changed from 1.0 wt.% to 2.0 wt.%, as verified by the experiments. This study provided the reference for the preparation of high-temperature applications alloy by constructing Nb-Zr gradient alloy.

Promoting effect of CO2 on NiCr oxidation: Atomistic origins based on first principles.

The adsorption and dissociation of CO2 on both perfect and oxygen-deficient α-Cr2O3 (0001) surfaces, alongside the subsequent incorporation of the resulting C into the oxide lattice and its impact on oxide growth, are investigated using first-principles calculations. Our findings reveal that oxygen vacancies significantly enhance CO2 adsorption and promote its stepwise decomposition into C and O atoms. The resulting C can spontaneously dissolve into the oxide lattice through the oxygen vacancies. The presence of bulk dissolved C in the Cr2O3 lattice substantially enhances the formation, migration, and clustering of oxygen vacancies in the bulk. These results provide an atomic-level understanding of how CO2 accelerates the oxidation of chromia-forming alloys, offering microscopic insights for controlling oxide growth and mitigating oxidation-induced degradation of high-temperature alloys.

Size effects and optimization during laser directed energy deposition on high thermal conductivity copper alloys

High-copper alloy/nickel-based high-temperature alloy bimetallic structures are widely utilized in critical components, such as thrust chambers of liquid rocket engines, water cooling circuits for fusion reactor deflectors, and electromagnetic railguns. Among various methods for fabricating Cu/Ni bimetallic structures, laser directed energy deposition (LDED) is considered one of the most promising techniques for depositing nickel-based high-temperature alloys onto high-copper alloy surfaces. In the LDED fabrication process, substrates with uneven thicknesses are a common. The process is characterized by its multi-parameter, high-sensitivity, and non-equilibrium solidification characteristics. Consequently, variations in substrate size can significantly affect molten pool morphology and fabrication stability. This study examines the size effect of a single track of LDED Inconel 718 (In718) on a CuCr0.8 high-copper alloy substrate. The results indicate a pronounced size effect when using a high thermal conductivity CuCr0.8 substrate, particularly regarding substrate thickness. By reducing the thermal conductivity of the CuCr0.8 substrate, the size effect is mitigated, improving the process adaptability of LDED. These findings provide valuable data for the laser processing of surfaces with uneven thickness and high thermal conductivity. They are expected to support the fabrication of variable thrust liquid rocket engines and advance the field of interplanetary exploration.

Enhanced oxidation resistance in nano-lamellar CoCrFeNiNbx (0.45 ≤ x ≤ 0.55) eutectic high entropy alloy during cyclic oxidation at 700–1100 °C

We report the superior oxidation resistance of nano-lamellar CoCrFeNiNbx (x = 0.45, 0.50, 0.55 atom ratio) eutectic high entropy alloy (EHEA) at 700–1100 °C. The as-cast microstructure comprises of nano-lamellar eutectic FCC+Laves phases. The oxidation kinetics followed the parabolic rate in between 700–800 °C, whereas, near-parabolic kinetics is followed at 900 °C. The addition of Nb improves the oxidation and spallation resistance of the EHEAs. A protective outer-oxide layer containing Cr2O3, FeCr2O4-type spinels, whereas, an inner-oxide layer containing Nb2O5, CrNbO4 were formed during oxidation. The mechanism of protection and the superiority of EHEAs as high temperature alloy are explored.

Noise-Aware Active Learning to Develop High-Temperature Shape Memory Alloys with Large Latent Heat.

Shape memory alloys (SMAs) with large latent heat absorbed/released during phase transformation at elevated temperatures benefit their potential application on thermal energy storage (TES) in high temperature environment like power plants, etc. The desired alloys can be designed quickly by searching the vast component space of doped NiTi-based SMAs via data-driven method, while be challenging with the noisy experimental data. A noise-aware active learning strategy is proposed to accelerate the design of SMAs with large latent heat at elevated phase transformation temperatures based on noisy data. The optimal noise level is estimated by minimizing the model error with incorporation of a range of noise levels as noise hyper-parameters into the noise-aware Kriging model. The employment of this strategy leads to the discovery of the alloy with latent heat of -36.08 J g-1, 9.2% larger than the best value (-33.04 J g-1) in the original training dataset within another four experiments. Additionally, the alloy represents high austenite finish temperature (481.71°C) and relatively small hysteresis. This promotes the latent heat TES application of SMAs in high temperature circumstance. It is expected that the noise-aware approach can be convenient for the accelerated materials design via the data-driven method with noisydata.

Analysis of High and Low Temperature Performance of Titanium Zirconium Molybdenum Alloy and High Temperature Alloy Brazed Joint

Abstract Using niobium as the intermediate layer and gold nickel (Au82-Ni) filler metal, TZM alloy and high-temperature alloy GH3128 were brazed. The brazed specimens were subjected to 400 cycles of high and low temperature cycling tests at temperatures ranging from 650 °C ∼ 680 °C (high temperature) to -196 °C (low temperature) for 10 minutes seperately. Then the microstructure variation before and after the experiment were observed and the shear strength of the specimens were tested at room temperature for 50 cycles of 400 high and low temperature testing.. The results show that the microstructure of the transition zone at the brazing interface after brazing is uniform and dense, with good wettability with the substrate and no defects such as cracks. The solder and substrate undergo diffusion reactions, and the molybdenum alloy, niobium, and niobium, high-temperature alloy had each form diffusion layers, formed intermetallic compounds on the brazing surface. After high and low temperature cycling, cracks exist in the braze seam between molybdenum alloy and niobium alloy. The cracking mode should be thermal fatigue based on the fracture morphology and phase analysis. The reasons of interface cracking are that due to different thermal expansion coefficients, low mutual solid solubility, and the formation of a large number of different types of intermetallic compounds, Mo and Nb materials have poor brazing compatibility and lower interface strength. Under cold and hot cycling conditions, brittle intermetallic compounds are prone to form crack source areas. As the number of cycles increases, the cracks gradually expand, ultimately leading to product leakage. In addition, the shear strength of brazed joints shows a decreasing trend with the increase of high and low temperature cycles in 400 high and low temperature tests.

Preparation and properties of ultra-high hardness Co-Cr-Mo-Nb-B high-temperature amorphous alloy coating

In this paper, a high temperature and amorphous alloy coating of Co26Cr26Mo26Nb7B15 was prepared by high-velocity oxy-fuel spraying. The phase structure, thermodynamic properties, hardness, friction and wear behaviors, and corrosion behavior and its mechanism were studied. The results showed that the glass transition temperature of the coating reached to 1058 K, and the hardness was as high as 1589.4 HV. The amorphous alloy coating of Co26Cr26Mo26Nb7B15 exhibited excellent wear resistance. Its friction coefficient was only 0.1152, which was about 25 % of 316 stainless steel, and the wear volume was only 0.1338 mm3. Additionally, the coating presented excellent corrosion resistance in 1 M hydrochloric acid solution, with the corrosion current density of 1.04 × 10−5 A·cm−2, and corrosion voltage of −0.32 V vs SCE.

Unique grain refinement mechanism of graphene oxide reinforced high-temperature titanium alloy matrix composite

Grain refinement is an effective way to improve the comprehensive mechanical properties of titanium matrix composites. In this work, the strong grain refinement effect of GO on 600 ℃ high-temperature titanium alloy prepared by hot isostatic pressing was found. The refinement mechanism was studied by experimental analysis, first-principles calculation and cellular automaton simulation. The α grain size of the composite with 0.50wt.% GO decreased by 53.2% compared with the matrix alloy. The direct effect of GO on grain refinement was weak. GO introduced C and O as α-stable elements to increase α phase content, resulting in the solid solubility of Si decreasing and fine (TiZr)6Si3 particles precipitating. (TiZr)6Si3 particles prevented dislocation from moving to accelerate continuous dynamic recrystallization nucleation and pinned grain boundary to inhibit grain growth. The results of cellular automaton simulation show that the inhibitory efficiency of (TiZr)6Si3 on grain growth was 4.7 times that of GO. The unique mechanism that GO promoted silicide particles precipitation and indirectly refined grain provided a design route for novel titanium matrix composites synergistically strengthened by two-dimensional nanosheets, in-situ nanoparticles and grain refinement.

Development of the interlayer alloy using for TLP diffusion bonding of GH3230 superalloy based on the CALPHAD method

The hot-end components of aero-engines and gas turbines not only require high-temperature alloys capable of withstanding extreme temperatures, but also demand welds with high-temperature-resistant properties. In this study, the CALPHAD method was employed, utilizing the thermodynamic theory of phase diagrams with Thermo-Calc software and the corresponding database, to design the interlayer composition for superalloy TLP diffusion connections. The optimization aimed to determine the interlayer material's solidus-liquidus and compound phase content, resulting in the selection of a new nickel-based interlayer material containing B as MPD, with Co and W as strengthening elements. Using GH3230 alloy as the research subject, TLP diffusion bonding experiments were conducted at a welding temperature of 1200 °C with a holding time of 4 h. The weld zone exhibited no defects, and the microstructure was identical to that of the GH3230 base metal, consisting entirely of a solid solution. High-temperature tensile tests revealed that fractures consistently occurred in the GH3230 base metal, indicating that the weld's strength significantly exceeded that of the base metal. The average tensile strength of GH3230 high-temperature alloy bar tensile simulated specimens is 899 MPa at room temperature and 213 MPa at high temperature. In addition, the 90° three-point bend test showed no cracking in the weld area, indicating adequate plasticity.

Grain growth in Ni50Ti30Hf20 high-temperature shape memory alloy processed by high-pressure torsion

Grain growth in Ni50Ti30Hf20 high-temperature shape memory alloy processed by high-pressure torsion

Enhanced thermal performance of CeYSZ coating on Ni-based high temperature alloy with a unique Y-doped Al2O3 barrier layer via cathodic plasma electrolytic deposition

Cathodic plasma electrolytic deposition (CPED) has shown considerable potential in producing high-performance thermal barrier coatings (TBCs) for components operating in extreme thermal environments, such as gas turbines and aviation engines. However, the dendritic and porous structures greatly limited the use of CPED-coatings in some harsh environments. In this study, one Y-doped Al2O3 (Y/A) barrier layer was prefabricated before the deposition of CeO2 and Y2O3 stabilized ZrO2 (CeYSZ) thermal barrier coating using CPED. The results suggested that the prefabricated Y/A barrier layer can attenuate the plasma bombardment and promote the uniform discharge, resulting in the formation of a thinner gas film layer on the cathode surface, which significantly avoided the course dendritic defects and improved the density of the CeYSZ coating from 6.788 g/cm³ to 6.978 g/cm³. Consequently, the thermal insulation temperature of Y/A-CeYSZ coatings exceeded that of CeYSZ coatings by a factor of 1.3, and the thermal cycling performance at 1300 °C demonstrated a 52.5% improvement. This study provided a valuable method for the development of novel CPED TBCs.

Comprehensive study of the effect of Hf and Ta co-doped MCrAlY bond coat on the high-temperature properties of thermal barrier coating

The MCrAlY bond coat is modified by reactive element (RE) Hf and refractory element Ta, and the high-temperature oxidation resistance of the thermal barrier coating (TBC) before and after the modification are investigated by comparative experiments. The experiments use high-velocity oxygen-fuel (HVOF) to prepare NiCoCrAlY and NiCoCrAlYHfTa bond coats on the surface of GH4099 high-temperature alloy, and then yttrium stabilized zirconia (YSZ) ceramic layers are prepared on the surface of the bond coat by atmospheric plasma spraying (APS), and cyclic oxidation is carried out in air at 1050 °C until failure. It is shown that the oxidation lifetime of the modified TBC reached 1992 h, which is one time higher than that of the unmodified TBC. The doping of Hf and Ta elements reduces the growth rate of the oxide layer, and these diffuse externally and combine with the internally diffused O to form HfO2 and Ta2O5 in the thermally grown oxide (TGO) layer, thereby improving the adhesion and mechanical properties of the oxide layer. In addition, the bond strength and thermal shock resistance of the TBCs are significantly improved after doping with Hf and Ta elements, which prolongs the lifetimes of the TBCs. In this paper, the morphology, structure, and properties of the modified TBCs are characterized to investigate the mechanism of the oxidation lifetime extension.

Material selection and design of intake blades for aircraft engines based on additive manufacturing

Abstract The intake blades of aircraft engines are mainly used to capture and guide external air into the engine and are the foundation of engine operation. Their materials and design are related to the performance level and reliability of the entire engine. The “additive” 3D printing manufacturing method has the advantages of high precision, low cost, less material waste, strong design, and a short research and development cycle. This article proposes the use of GH4169 high-temperature alloy as the 3D printing material for the service requirements of aircraft engine intake blades, constructs a 3D printing model, and designs and realizes the 3D printing of engine intake blades.

Отримання жароміцного гомогенного сплаву методом пресування та спікання суміші порошків (Nb-21Ti-5Al-10Cr-7Mo) ат. %

Multicomponent high temperature strength alloys of the Nb-Ti-Al system, alloyed with Cr, Zr, Mo and Si, with a specific gravity of 6.3 - 7.4 g/cm3, have proven extremely promising in aviation and space technology. However, their physical and chemical features are associated with the high activity of the components, with a significant difference in melting temperatures (from Tmel. Mo – 2617 °C to Tmel. Al – 660 °C) and different specific gravity (from 10.2 g/cm3- Mo up to 2.7 g/cm3- Al), is a big problem for their production. The long crystallization interval of cast alloys of this system, thermophysical features of their crystallization, determine the possibility of formation of dendritic structures, the development of dendritic liquation and segregation of low- or high-temperature intermetallics and eutectics, the tendency to the formation of crystallization cracks, which reduces the operational characteristics of cast alloys. In this regard, it became necessary to investigate the possibilities of obtaining an alloy by the method of powder metallurgy. The purpose of this work was to obtain a homogeneous alloy, to study changes in the grain structure, phase transformations and mechanical properties of the material at various stages of processing in the process of obtaining a homogeneous alloy structure by powder metallurgy methods. The need to protect powder components from oxidation, formation of nitrides, carbides during technological operations at temperatures above 200 °C (high-purity argon) has been established. The optimal duration of intensive grinding of a mixture of powders and granules of raw materials has been worked out, which makes it possible to control the uniformity of the size of the particles of the mixture components, porosity and homogeneity of the alloy. The optimal duration of grinding is 30 minutes, during which the most homogeneous mixture in terms of particle size is formed. The optimal annealing mode was established, which ensures the achievement of homogenization of the alloy, phase transformations at the boundaries of the contact of component particles, and changes in grain sizes. Microstructural and X-ray structural analysis of the samples was carried out, their microhardness and grain dispersion were determined. Keyword: high-temperature strength niobium alloys, physical and chemical features, powder metallurgy, homogeneity, microstructure, mechanical properties, phase composition.

Effect of rotary swaging and annealing on mechanical properties and microstructure evolution of aeroengine high-temperature alloy steel tube

Effect of rotary swaging and annealing on mechanical properties and microstructure evolution of aeroengine high-temperature alloy steel tube

Optimization of Machining Parameters for Nimonic PE16 Using Machine Learning Models

Machining high-temperature alloys such as Nimonic PE16 demands precise control of machining parameters to achieve desired outcomes while minimizing tool wear and optimizing surface finish. In this study, we propose using machine learning regression models combined with synthetic data and response surface methodology strategies to optimize machining parameters for PE16. We aim to develop a predictive model that accurately estimates optimal cutting speeds and feed rates based on key output parameters, including cutting forces and surface roughness. Our methodology involves collecting experimental data from controlled machining tests conducted on PE16 samples under varying conditions. We used the datasets to train and validate regression models to establish correlations between input parameters and machining outcomes. The performance of each model is evaluated based on metrics such as mean absolute error and coefficient of determination. These metrics show relationships within the data and can determine a model’s success. The proposed machine learning framework offers a data-driven approach to optimize machining processes for PE16, facilitating enhanced efficiency, productivity, and quality in nuclear and other high-performance applications. Our findings contribute to understanding machining dynamics in challenging materials and provide valuable insights for intelligent machining systems.

Development and approval of the procedure of high-temperature uniaxial creep strength tests of difficult -to-weld high-temperature nickel alloys specimens with microplasma powder deposition

Development and approval of the procedure of high-temperature uniaxial creep strength tests of difficult -to-weld high-temperature nickel alloys specimens with microplasma powder deposition