Single Crystal Nickel Research Articles

Analysis of the features of the operating conditions of modern gas turbine blades and review of methods for determining their high-temperature strength parameters

The subject of the study is modern methods and materials for the manufacture of gas turbine blades, as well as approaches and methods for assessing their dynamic and static strength under high-temperature loading. The first purpose of the article is to describe the main methods of manufacturing turbine blades, provide examples of the materials used and the features of their crystal structure. The second purpose of the article is to review approaches to ensuring the dynamic and static strength parameters of single-crystal turbine blades, in particular, to avoid dangerous resonance modes, to study the parameters of anisotropic creep, high-temperature fatigue life, and long-term strength. The goal of the article is to highlight the main advantages and disadvantages of existing methods, approaches and techniques for assessing and ensuring high-temperature strength parameters of turbine blades under static and dynamic loading, in order to select the objectives of further research. Methods used to create the publication: methods of analysis and comparison, which were used to search and compare open literature sources of information in accordance with the purpose of the article, as well as the method of deduction, which was used to identify the main shortcomings of existing methods for assessing the high-temperature strength of gas turbine blades under static and dynamic loading to outline the goals of further research. The following results have been obtained. Literature sources related to the methods of manufacturing turbine blades, namely, directional crystallization and single-crystal casting, were analyzed. The advantages of single-crystal alloys for the manufacture of turbine blades, namely increased heat strength, heat resistance, fatigue strength, durability and crack resistance, are emphasized. The main modern methods for assessing the high-temperature strength of gas turbine blades with regard to the anisotropic characteristics of single-crystal alloys are analyzed and described. Conclusions. This publication presents information about gas turbine blades, in particular, provides meaningful information about the methods of their manufacture, as well as the materials used to produce them. The study analyses and identifies the main damaging effects on gas turbine blades during their operation. The material describes the achievements of scientists who have developed numerical and experimental methods for assessing the impact of the anisotropic characteristics of single-crystal nickel heat-resistant alloys on the fatigue strength, durability and creep of turbine blades.

Enhanced Long-Term Stability of Crystalline Nickel-Boride (Ni23B6) Electrocatalyst by Encapsulation with Hexagonal Boron Nitride.

Nickel boride catalysts show great potential as low-cost and efficient alternatives to noble-metal catalysts in acidic media; however, synthesizing and isolating a specific phase and composition of nickel boride is nontrivial, and issues persist in their long-term stability as electrocatalysts. Here, a single-crystal nickel boride, Ni23B6, is reported which exhibits high electrocatalytic activity for the hydrogen evolution reaction (HER) in an acidic solution, and that its poor long-term stability can be overcome via encapsulation by single-crystal trilayer hexagonal boron nitride (hBN) film. Interestingly, hBN-covered Ni23B6 on a Ni substrate shows an identical overpotential of 52mV at a current density of 10mA cm-2 to that of bare Ni23B6. This phenomenon indicates that the single-crystalline hBN layer is catalytically transparent and does not obstruct HER activation. The hBN/Ni23B6/Ni has remarkable long-term stability with negligible changes to its polarization curves for 2000 cycles, whereas the Ni23B6/Ni shows significant degradation after 650 cycles. Furthermore, chronoamperometric measurements indicate that stability is preserved for >20h. Long-term stability tests also reveal that the surface morphology and chemical structure of the hBN/Ni23B6/Ni electrode remain preserved. This work provides a model for the practical design of robust and durable electrochemical catalysts through the use of hBN encapsulation.

Negative Creep of Single Crystals of Nickel–Based Superalloys

Negative Creep of Single Crystals of Nickel–Based Superalloys

Prestrain Guided Yield of Large Single-Crystal Nickel Foils with High-Index Facets.

Single-crystal metal foils with high-index facets are currently being investigated owing to their potential application in the epitaxial growth of high-quality van der Waals film materials, electrochemical catalysis, gas sensing, and other fields. However, the controllable synthesis of large single-crystal metal foils with high-index facets remains a great challenge because high-index facets with high surface energy are not preferentially formed thermodynamically and kinetically. Herein, single-crystal nickel foils with a series of high-index facets are efficiently prepared by applying prestrain energy engineering technique, with the largest single-crystal foil exceeding 5×8 cm2 in size. In terms of thermodynamics, the internal mechanism of prestrain regulation on the formation of high-index facets is proposed. Molecular dynamics simulation is utilized to replicate and explain the phenomenon of multiple crystallographic orientations resulting from prestrain regulation. Additionally, large-sized and high-quality graphite films are successfully fabricated on single-crystal Ni(012) foils. Compared to the polycrystalline nickel, the graphite/single-crystal Ni(012) foil composites show more than five-fold increase in thermal conductivity, thereby showing great potential applications in thermal management. This study hence presents a novel approach for the preparation of single-crystal nickel foils with high-index facets, which is beneficial for the epitaxial growth of certain two-dimensionalmaterials.

Bevel-edge epitaxy of ferroelectric rhombohedral boron nitride single crystal.

Within the family of two-dimensional dielectrics, rhombohedral boron nitride (rBN) is considerably promising owing to having not only the superior properties of hexagonal boron nitride1-4-including low permittivity and dissipation, strong electrical insulation, good chemical stability, high thermal conductivity and atomic flatness without dangling bonds-but also useful optical nonlinearity and interfacial ferroelectricity originating from the broken in-plane and out-of-plane centrosymmetry5-23. However, the preparation of large-sized single-crystal rBN layers remains a challenge24-26, owing to the requisite unprecedented growth controls to coordinate the lattice orientation of each layer and the sliding vector of every interface. Here we report a facile methodology using bevel-edge epitaxy to prepare centimetre-sized single-crystal rBN layers with exact interlayer ABC stacking on a vicinal nickel surface. We realized successful accurate fabrication over a single-crystal nickel substrate with bunched step edges of the terrace facet (100) at the bevel facet (110), which simultaneously guided the consistent boron-nitrogen bond orientation in each BN layer and the rhombohedral stacking of BN layers via nucleation near each bevel facet. The pure rhombohedral phase of the as-grown BN layers was verified, and consequently showed robust, homogeneous and switchable ferroelectricity with a high Curie temperature. Our work provides an effective route for accurate stacking-controlled growth of single-crystal two-dimensional layers and presents a foundation for applicable multifunctional devices based on stacked two-dimensional materials.

A bimetal strategy for suppressing oxygen release of 4.6V high-voltage single-crystal high-nickel cathode

High-voltage cathode materials, such as single-crystal high-nickel layered oxide materials, are a necessary condition for achieving high energy density lithium-ion batteries, but they have to be accompanied by the structural instability and irreversible release of lattice oxygen during operation, posing serious safety hazards. Here, to solve the lattice oxygen release issue of single-crystal high-nickel cathode, we propose an improved strategy for overall cathode by synchronously addressing interface and lattice instability, ensuring stable operation at a high voltage up to 4.6 V. By Al-doping, in the bulk phase, we intensify the charge transfer between transition metals and oxygen, and the columnar effect caused by doped atoms effectively alleviates internal strain, thereby significantly limiting lattice shrinkage and then suppressing oxygen release. On the other hand, the protective layer of LiNbO3 as the fast ion conductor formed at the cathode interface suppresses parasitic reactions and hinders lattice oxygen loss caused by dissolution of transition metals. Therefore, after 200 cycles at a cut-off voltage of 4.6 V, our cathode material still maintains a capacity retention rate of 89.1%. Density functional theory (DFT) calculations predict the effective suppression of oxygen release for the modified cathode materials, which has been further confirmed by differential electrochemical mass spectrometry (DEMS) tests. This work provides a new perspective for solving the problem of oxygen release under high cut-off voltage conditions for single crystal high nickel cathode.

Effects of high energy laser peening followed by pre-hot corrosion on stress relaxation, microhardness and fatigue life and strength of single crystal nickel CMSX-4® superalloy

This study investigated the stress relaxation and fatigue life and strength of laser peened single crystal nickel superalloy specimens following hot corrosion exposure and then fatigue testing compared to un-peened and shot peened specimens. The specimens were treated by conventional laser peening and a new cyclic laser peening plus thermal microstructure engineering process. Stress measurements by slitting showed the plastic penetration depth of laser peening exceeded shot peening by a factor of 24. Un-peened and peened specimens were exposed to sulphate corrosives at 700°C for 300 hours and then fatigue tested. Tests of five non-laser peened specimens all failed in low cycle fatigue regime whereas three identically tested laser peened specimens all achieved multi-million-cycle runout without failure, indicating fully consistent large benefit for life by laser peening. Additional tests showed fatigue strength improvement of 2:1 by laser peening.

Impact Velocity-Dependent Patterns and Mechanisms of Spalling Behavior in Single Crystal Nickel

To reveal the impact velocity (U<sub>p</sub>) effect on the spalling and fracture behavior of single crystal nickel, a non-equilibrium molecular dynamics approach is performed to investigate the free surface velocity curve, radial distribution function, atomic crystal structures, dislocations, and void evolution process. The results show that the critical U<sub>p</sub> for spalling behavior in single crystal nickel is 1.5 km/s, the spallation mechanism is classical spallation damage (U<sub>p</sub>≤1.5 km/s) and micro-spallation damage (U<sub>p</sub>＞1.5 km/s). The number and distribution area, and stress distribution area under micro-spallation damage much higher than those under classical spallation damage. Analyzed the influence of impact velocity on the classical spalling damage behavior (U<sub>p</sub> ≤ 1.5 km/s) and obtained the corresponding spalling strength, an accident of spalling strength occurs at the U<sub>p</sub> of 1.3 km/s. The spalling strength of single crystal nickel is influenced by the combined effects of stacking faults, phase transformation, and dislocation mechanisms. The nucleation and emission of dislocations increase lead to a decrease in the spalling strength. When U<sub>p</sub> <1.3 km/s, spalling damage is primarily influenced by stacking faults. When U<sub>p</sub> =1.3 km/s, spalling strength is mainly affected by the competition between stacking faults and phase transformation. When U<sub>p</sub> >1.3 km/s, spalling strength is predominantly influenced by the body-centered cubic (BCC) phase transformation mechanism (transformation path: FCC → BCT → BCC). This study reveals the impact velocitydependent patterns, mechanisms, and effects on spalling damage and fracture, providing a theoretical basis for the protective application of nickel-based materials under extreme impact conditions.

Mitigating hydrogen gas evolution in high nickel cathodes using single-crystalline NCM particles

Single-crystal nickel cobalt manganese oxide cathodes significantly reduce hydrogen gas evolution due to their smaller specific surface area and enhanced structural stability.

Surface gradient structures in single-crystal nickel alloy induced by ultrasonic-assisted high-speed grinding

The gradient structures in surface layer of single-crystal nickel alloy (SX alloy) were produced (i.e., nanograin, submicron grain and coarse single crystal of bulk material) by means of ultrasonic-assisted high-speed grinding (UAHSG). The surface layer with a grain size gradient (from 29.7 to 111.8 nm) along depth from the treated surface featured impressive nano-indentation hardness (up to 12.1 GPa) beyond the initial SX alloy. The coupled effects of high rotation speed of abrasive grain (100 m/s) and the severe ultrasonic vibration impact (up to 4.3 times per contact cycle) induced large strain (up to 6.67) and ultrahigh strain rate (∼109 s−1), resulting in the superiority of such a structure gradient. This study suggests a new approach of UAHSG that can not only achieve high machining efficiency, but also make nickel alloy stronger by tailoring the surface layer gradient structures.

Tuning Mo/W ratio to improve high temperature oxidation resistance of single crystal nickel base superalloys

The effect of different Mo/W ratios of three single crystal nickel base superalloys on the oxidation behavior was investigated at 1100 °C. Both isothermal and cyclic oxidation tests showed that increasing Mo/W ratio corresponds to lower weight change and improved resistance. The microscopic observation uncovers that the harmful effect of Mo is limited by the dense Al2O3 scale. In contrast, excessive W leads to fast growth of interlayer and its premature spallation. This research proposes and verifies a new way to improve oxidation resistance of alloy, namely, balancing the harmful effect of refractory elements.

Computer Simulation and Optimization of the Single-Crystal Nickel Superalloy Compositions: IV. Computer Method for Optimizing the Superalloy Composition

Computer Simulation and Optimization of the Single-Crystal Nickel Superalloy Compositions: IV. Computer Method for Optimizing the Superalloy Composition

Toward single crystal nickel fabrication using WAAM – A first report

The present study is focused on investigating the feasibility of additive manufacturing of single crystal nickel components using MIG processed wire arc additive manufacturing (WAAM) technique. The feasibility was validated by depositing the material first on 99.999 % pure polycrystalline nickel substrate and then onto a 99.995 % pure single crystal nickel specimen oriented in <111> direction. Optical microscopy and EBSD results prove the possibility for regions of single crystal to be deposited. The process yielded distinct regions of single crystal. Columnar and equiaxed grains occurred in a region with the highest local thermal gradient and slowest solidification rate. EBSD analysis confirmed that the single crystal region revealed in optical microscopy was in one orientation and the etchant was effective in highlighting individual grain boundaries.

Development of modular cryogenic indentation apparatus for investigating micro-region mechanical properties of materials

High-precision cryogenic micromechanical testing apparatuses are of significant importance in investigating the micro-region mechanical properties and deformation behaviors of materials at cryogenic temperatures. In this study, a modular cryogenic indentation apparatus was designed and developed utilizing a contact-atmosphere hybrid refrigeration technique with a minimum temperature of −150 °C. The temperature of both the indenter tip and the specimen was independently controlled through a dual-channel proportional–integral–derivative (PID) feedback loop to eliminate contact thermal drift to within 0.1 nm/s. The application of cryogenic nitrogen (N2) atmosphere refrigeration eliminated additional stiffness at the indenter tip completely. The feasibility of the apparatus was demonstrated through calibrations and tests conducted on standard fused silica and single crystal nickel. Highly accurate indentation curves and micro-region mechanical properties of single crystal nickel were obtained at variable cryogenic temperatures. With decreasing temperature, both slip bands and pile-up around residual indentation imprints were weakened. Notably, at −150 °C, the slip bands disappeared, and the phenomenon of pile-up was replaced by sink-in. This developed cryogenic indentation apparatus will be a powerful tool to reveal the effect of cryogenic temperatures on the evolution mechanisms of materials’ micro-region mechanical properties.

Ton-scale preparation of single-crystal Ni-rich ternary cathode materials for high-performance lithium ion batteries

Single-crystal nickel (Ni)-rich cathode materials (Li[Ni [Formula: see text]Co[Formula: see text]Mn[Formula: see text][Formula: see text][Formula: see text][Formula: see text]]O2, (NCMs)) of lithium ion batteries (LIBs) have displayed promising application potential due to the merits of stable structure, minor side reaction, and high energy density. The Ni[Formula: see text]Co[Formula: see text]Mn[Formula: see text][Formula: see text][Formula: see text][Formula: see text](OH)2 as the precursor of single-crystal NCM faces the issues of tedious preparation process and serious pollutant emission for traditional preparation methods during the industrial preparation. Herein, an improved continuous two-step spray pyrolysis strategy is adopted to prepare the precursor of single-crystal NCM. Combining with the industrial devices, ton-scale preparation of single-crystal NCM is realized after dynamic lithiation post-treatment. This improved strategy not only shortens the preparation process, but also reduces metal segregation and sintering temperature, effectively balancing the cost control and production efficiency. The samples sintering at 850[Formula: see text]C show uniform morphology with a diameter of 4.5 [Formula: see text]m and delivers an initial discharge capacity of 169 mAh/g at 0.1 C after 100 cycles. This work provides a new route for the industrial preparation single-crystal NCM cathode materials of LIBs.

The Manufacturing and Experimental Validation of a Nickel Superalloy Double-Wall, Effusion Test Specimen

Abstract With the hot stage of a modern aeroengine operating with combustor firing temperatures well beyond the melting point of the nickel superalloys from which the turbine blades are manufactured, developments to the methods of cooling of these components are required to advance performance. Double-wall, effusion systems exhibit a quasi-transpiration like cooling effect with recent work demonstrating their exceptional cooling performance. Such systems are characterized by two walls, one with impingement holes and the other with film cooling holes, that are mechanically and thermally connected via pedestals. However, manufacturing such geometries from single-crystal nickel superalloys remains a significant barrier to entry into service. This paper presents a method of manufacturing double-wall effusion specimens from a nickel superalloy commonly used in modern commercial high-pressure turbine components. The method maintains the mechanical integrity associated with nickel superalloys. Details of the method are presented alongside X-ray and GOM laser scan data of a flat-plate test article that demonstrates the success of the manufacturing process. Aerothermal testing of the specimen in a bespoke recirculating wind-tunnel facility was undertaken in which the overall cooling effectiveness of the system is obtained. The results reaffirm the excellent cooling performance of double-wall, effusion systems and further validate the manufacturing methodology as a method by which to realize enhanced cooling effectiveness in service.

On the role of vacancy-hydrogen complexes on dislocation nucleation and propagation in metals

New insights are provided into the role of vacancy-hydrogen (VaH) complexes, compared to the hydrogen atoms alone, on hydrogen embrittlement of nickel. The effect of the concentration of hydrogen atoms and VaH complexes is investigated in different crystal orientations on dislocation emission and propagation in single crystal of nickel using atomistic simulations. At first, embrittlement is studied on the basis of unstable and stable stacking fault energies as well as fracture energy to quantify the embrittlement ratio (unstable stacking fault energy/fracture energy). It is found that VaH complexes lead to high embrittlement compared to H atoms alone. Next, dislocation emission and propagation at pre-cracked single crystal crack-tip are investigated under Mode-I loading. Depending upon the elastic interaction energy and misfit volume, high local concentrations at the crack front lead to the formation of nickel-hydride and nickel-hydride with vacancies phases. These phases are shown to cause softening due to earlier and increased dislocation emission from the interface region. On the other hand, dislocation propagation under the random distribution of hydrogen atoms and VaH complexes at the crack front or along the slip plane shows that VaH complexes lead to hardening that corroborates well with the increased shear stresses observed along the slip plane. Further, VaH complexes lead to the disintegration of partial dislocation and a decrease in dislocation travel distance with respect to time. The softening during emission and hardening during propagation and disintegration of partial dislocation loops due to VaH complexes fit the experimental observations of various dislocation structures on fractured surfaces in the presence of hydrogen, as reported in literature.

Effect of free surfaces on localized plastic deformation in single-crystal nickel containing helium bubbles and radiation-induced self-interstitial atom clusters

This paper presents molecular dynamics (MD) simulations of plastic deformation in single-crystal Ni models containing internal distributions of helium (He) bubbles and self-interstitial atom (SIA) clusters corresponding to experimental characterization of ex-service Inconel X-750 components. We simulate single crystals with and without free surfaces at room temperature and 588K, the latter temperature corresponding to the Inconel X-750 service conditions. Both models are deformed under multiple slip to a maximum deviatoric strain of ∼10 %. A dislocation slip band forms in the model without free surfaces, but not in the model with free surfaces. However, the latter exhibits nano-twin nucleation from surfaces. Helium (He) bubbles that overlap with a slip band or a nano-twinned region deform more severely than other bubbles in the model. Nevertheless, the bubbles do not link up and do not form configurations that resemble incipient cracks.

Ultrahigh-power all binder-free hybrid supercapacitors based on single-crystal hexagonal nanorods of molecular sieve VSB-5 hierarchical electrodes

BackgroundMolecular sieve Versailles Santa Barbara-5 (VSB-5) is a highly porous nanomaterial for electrochemical supercapacitor. MethodsA facile hydrothermal method is used to directly synthesize VSB-5 nanorods onto the Nickel Foam (NF). Significant findingsIn this work, one-dimensional single-crystal hydrogen nickel phosphate hydroxide hydrate (Ni20[(OH)12(H2O)6][(HPO4)8(PO4)4]·12H2O, also denotes as VSB-5, hexagonal nanorods arrays are successfully synthesized on NF via a hydrothermal method, and applied them as positive electrodes for hybrid supercapacitor (HSC). The resultant open framework of VSB-5 with unique nanochannels provides the synchronous advantages of a large surface area with numerous active sites for enhancing faradic redox reactions and abundant pathways for promoting electrolyte ions diffusion, thus leading to excellent energy storage behavior. Furthermore, the HSC is fabricated by paring the direct growth of carbon nanotubes (CNTs) on NF as the electrical-double-layer-capacitor negative electrode. Both the VSB-5/NF and CNTs/NF electrodes are binder-free hierarchical structures, owning the lowest interfacial resistivities between active materials and current collects, avoiding the aggregation issues to allow the facile diffusion of electrolyte for maximally utilizing the surface area. The resultant all binder-free VSB-5/NF//CNTs/NF HSC shows remarkable electrochemical performance, which delivers a maximum energy density of 46.9 W h kg−1 at a power density of 1225 W kg−1 with excellent capacity retention of 98.18% after 10,000 cycles.

Impact of Morphology of Polycrystalline and Single Crystal Nickel Rich Cathode Particles on Performance

High nickel cathode material (NMC 811) is great candidate for high performance batteries. It has high specific capacity and lower utilization of cobalt. The morphology of the cathode particles is studied in a comprehensive manner, from the impact of synthesis parameters on primary particle size, to experimental characterization and replicating the key morphological features in computational model to elucidate the morphological features critical to the performance. The polycrystalline micron sized secondary particle is comprised of thousands of nanometers sized primary particles. The single crystal is generally 2 to 3 microns in size. The “single crystal” cathode particle may be cluster of few single crystals. The length scales of primary and secondary particles as well as internal porosity of polycrystalline cathode particles changes the characteristic diffusion length as well as surface area available for electrochemical reaction. Similarly, for single crystal, the size and the degree of clustering changes the diffusion characteristics and surface area. These variations are reflected in specific capacities obtained at different C-rates. Gaining an in-depth understanding of correlation of morphological features to performance would be helpful in directing the synthesis process. Figure 1