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Prussian blue analogues with tunable open channels are of fundamental and technological importance for energy storage systems. Herein, a novel facile synthesis of nickel-cobalt hexacyanoferrate/reduced graphene oxide (denoted as Ni-CoHCF/rGO) nanocomposite is realized by a reverse microemulsion method. The very fine Ni-CoHCF nanoparticles (10–20 nm) are homogeneously anchored on the surface of reduced graphene oxide by electrostatic adsorption and reduced graphene oxide is well-separated by Ni-CoHCF particles. Benefiting from the combined advantages of this structure, the Ni-. It CoHCF/rGO nanocomposite can be used as electrodes for both supercapacitors and sodium ion batteries exhibits excellent pseudocapacitve performance in terms of high specific capacitance of 466 F g −1 at 0.2 A g −1 and 350 F g −1 at 10 A g −1 , along with high cycling stabilities. As a cathode material for sodium ion batteries, it also demonstrates a high reversible capacity of 118 mAh g −1 at 0.1 A g −1 , good rate capability, and superior cycling stability. These results suggest its potential as an efficient electrode for high-performance energy storage and renewable delivery devices. [ABSTRACT FROM AUTHOR]

γ′-strengthened CoNi-based superalloys containing Ti and Ta are studied to investigate the γ′ stability after long-term aging at 900 °C. Both thermodynamic predictions and experimental observations suggest that there is no formation of CoAl or Co 3 W phases, indicating that the γ′ phase remains stable in the investigated CoNi-based superalloys. Typical γ/γ′ structure with a relatively high amount of γ′ phase remains in the microstructures of explored CoNi-based superalloys containing Ti and Ta after aging for 3000 h. The secondary MC carbides separate out from γ matrix during aging and different orientation relationships between MC and matrix exist for the explored CoNi-based superalloys: (100) γ // (100) MC , [ 001 ] γ // [ 001 ] MC for the alloy with Ti; (11 1 ¯ ) γ // ( 1 ¯ 1 1 ¯ ) MC , [ 011 ] γ // [ 011 ] MC for the alloy with Ta. Nanoindentation was performed to evaluate the mechanical properties of individual γ channel and γ′ precipitate. It is found that indentation modulus of γ′ phase in the explored CoNi-based superalloys locate between those of Ni 3 Al and Co 3 (Al, W) alloys, and Ta exhibits stronger strengthening effects as compared to that of Ti. • γ′ phases are stable in CoNi-base alloys after long-term aging at 900 °C. • Young's modulus of γ′ in CoNi-base alloys are between those of Ni 3 Al and Co 3 (Al,W). • Ta has a stronger strengthening effect on γ′ than Ti. [ABSTRACT FROM AUTHOR]

In present work, a multiphase Ni 3 Al-based intermetallic alloy with complex components of γ'+γ dendrite comprising extremely high volume fraction (81 vol %) of γ′ phase and interdendritic β phase is investigated, the microstructure evolution and phase transformation behavior tailored by different solution cooling rates are studied by applying different cooling methods of water cooling (WC, 138 °C/s), air cooling (AC, 72 °C/s), and furnace cooling (FC, 0.05 °C/s) after solution treatment at 1200 °C for 10 h. Results show that the cubic degree, size and volume fraction of cuboidal primary γ′ as well as size of spherical secondary γ′ particles in the γ'+γ dendrite are improved by decreasing cooling rates, and the average sizes of the primary and secondary γ′ particles are found to meet logarithmic relationships with cooling rates. There are three kinds of precipitates in the interdendritic β phase resulted from different cooling methods, i.e., the rod-like Cr 3 C 2 carbides, the semi-spherical α-Cr particles, and the long acicular γ′ precipitates. The lower cooling rate decreases the number of rod-like Cr 3 C 2 carbides, increases the number and size of the semi-spherical α-Cr particles, and promotes the formation of long acicular γ′ precipitates in the interdendritic β-matrix. The semi-spherical α-Cr particles play the role of pinning dislocations in the β-matrix and have the orientation relationship of [‾110] α-Cr //[‾110] β-matrix. In addition, the precipitation of semi-spherical α-Cr particles in β-matrix is observed to accomplish in two sequential stages and grow in an onion-like ordered way. Stacking faults existed in partial of α-Cr particles due to the nanotwins in β-matrix. Microtwins are observed in the interdendritic β-matrix after water cooling, which have a bimodal configuration of nanotwins at the microtwinning boundaries and interior stacking faults. Besides, γ′-envelope formed between the γ'+γ dendrite and interdendritic β phase dependent on the solution cooling processes. Image 1 • Re-precipitation sizes of primary and secondary γ′ particles have the logarithmic relationship with solution cooling rates. • Microtwins in the β-matrix have a bimodal configuration of nanotwins at their boundary and interior stacking faults. • Precipitation pattern and growth mode of semi-spherical α-Cr particles in β-matrix phase after air cooling. • Precipitation behaviors influenced by solution cooling rates of precipitates in the interdendritic β. [ABSTRACT FROM AUTHOR]

Coarse columnar grains are always present in nickel-based superalloys fabricated by laser powder bed fusion (LPBF), which not only causes anisotropy in mechanical properties, but also increases the hot cracking susceptibility of the alloys. Generally, the addition of nucleating agents is a common consideration for grain refinement. However, the intrinsic ultra-high thermal gradient and cooling rate of the LPBF process result in significant differences in grain nucleation and growth compared to conventional casting. The ultra-high thermal gradient of the LPBF process severely inhibits constitutional supercooling, which significantly reduces the heterogeneous nucleation efficiency of nickel-based superalloys. In this work, we introduced Zr into Haynes 230 alloy to improve constitutional supercooling of the LPBF molten pool during solidification and investigated the individual/synergistic effects of nucleating agent (TiC particles) and solute (Zr atoms) addition on the grain refinement of Haynes 230 alloy. It was found that the columnar grain size and texture intensity of LPBF fabricated Haynes 230 alloys were dramatically decreased with Zr and TiC co-addition, which obviously improved the mechanical properties as well as weakened its anisotropy. Our work revealed that inhibition of cell epitaxial growth and promotion of cell nucleation are necessary conditions to refine the grain size of LPBF fabricated nickel-based superalloys. Solutes with high growth restriction factor (Q value), such as Zr in our work, can rapidly generate constitutional supercooling, thereby obviously improving the heterogeneous nucleation efficiency of nucleating agents in nickel-based superalloy during the LPBF process. [Display omitted] [ABSTRACT FROM AUTHOR]

Precipitation and growth behavior of γ′ (Ni3Al) phase are crucial to evaluate the service stability of superalloys. In this work, precipitation and growth mechanisms of γ′ phase in different areas of a newly designed Ni3Al-based superalloy were investigated under short-term thermal exposure conditions. Results showed that twinning γ′ phase and foliated γ′ phase precipitated in eutectic area and interface area, respectively. γ′ phase went through from sphere to precursor plate and plate twinning eventually in eutectic area, which was related to preferred orientation of γ′ phase and local segregation of Al element. Dislocation and sidestep interface between matrix and the precipitation were the main reasons for the formation of twinning γ′ phase. Meanwhile, the morphology of γ′ phases in interface area went through a process from sphere to rod-like, and foliated γ′ phases formed eventually which grew toward eutectic areas with thermal exposure time increasing. Vacancies, distortions caused by different thermal expansion coefficients, lattice mismatch between dual-phase area and eutectic area contributed to the formation and growth of spherical phase. Moreover, reduction in interface energy promoted the transformation of spherical phase to rod-like and foliated γ′ phases. In addition, concentration gradient of Al element and adequate holding time were responsible for the directional growth of foliated γ′ phase. [ABSTRACT FROM AUTHOR]

• Rapid solidification rate promotes high nucleation burst of α-Cr precipitates (sources for dislocations). • Dislocations act as precursor to stacking faults and microtwinning. • Martensite plates with a high density of stacking faults and multiple microtwins are formed. Influence of solidification rate on the interdendritic microstructure evolution of a multiphase Ni 3 Al-based superalloy was investigated. Compared to the original as cast sample, rapid solidification rate leads to high nucleation burst of α-Cr precipitates in spray casting alloy, which promotes the transformation from b.c.c. B2 β phase to f.c.t. L1 0 martensite plates with high density of stacking faults and microtwins in interdendritic regions. [ABSTRACT FROM AUTHOR]

Abstract Inconel 718 is a widely used nickel-based superalloy in aircraft engines during the past decades, whose elevated temperature strength derives from disc-shaped gamma double prime (γ″) in three perpendicular variants plus less spherical gamma prime (γ′) precipitates. In present work, we observed an abnormal γ″ variant with tailored orientation and shape in directly aged cold-rolled Inconel 718, creep tests proved its substantial benefits in improving creep resistance at 650 °C superior to commonly perpendicular γ″ variants. The results can provide new insights for processing optimization and second-particle configuration design to maximize the strengthening effect of γ″ phase in 718-type superalloys. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Allvac 718Plus alloy is a newly-developed Ni-based superalloy with excellent thermal stability and mechanical performance at elevated temperatures up to 704 °C. The precipitation behavior of the rapidly-solidified Allvac 718Plus superalloy during aging is systematically investigated in this work. The microstructure evolutions of the strengthening γ' phase and the γ'/γ″ co-precipitates during aging are examined. During aging, the "duplet" γ'/γ″ and "triplet" γ″/γ'/γ″ occur and then disappear due to the dissolution of γ″ phase, which is promoted by the δ precipitation. On the contrary, the "triplet" γ'/γ″/γ' forms and remains after aging, resulting from the low diffusion rate of solute atoms through the spheroidal γ' precipitates. The lamellar δ-Ni 3 Nb phase occurs at grain boundaries. Its size and content increase with the prolongation of aging time. After long-term thermal exposure, the hexagonal η phase forms at the δ-γ interface due to the variations of local chemical composition, and then the tetragonal Cr-rich σ phase nucleates adjacent to the δ and η particles because of the segregation of Cr atoms rejected from the δ and η particles. • The rapidly-solidified γ-matrix of 718Plus is obtained with a supersaturated solid solution and a high density of defects. • The dissolution of ellipsoidal γ″ results in the disappearance of the "duplet" γ'/γ″ and "triplet" γ″/γ'/γ″. • The "triplet" γ'/γ″/γ' is remained due to the low diffusion rate of solute atoms through the spheroidal γ' precipitates. • The lamellar δ forms first and the η and σ phases successively nucleate at the δ-γ interface after long-time thermal exposure. [ABSTRACT FROM AUTHOR]

A polycrystalline Ni 3 Al-based superalloy was joined through transient liquid phase (TLP) bonding technique. A post bond heat treatment (PBHT) was successively conducted. Creep tests of the TLP and TLP + PBHT specimens were then carried out under 800 °C and 160 MPa. The creep deformation and fracture behaviors were further investigated through interrupted creep tests. During the PBHT procedure, microstructure evolution of the joint occurred with creep life prolonged from 64 h to 368 h. The superdislocations in TLP and TLP + PBHT specimens were determined to study the γ′ phase shearing modes. Both individual superdislocations and APB-coupled partial dislocation pairs are observed. The variation of dominate superdislocation configurations among different joint zones and the evolution of the superdislocations during the creep process are discovered. Besides, the formation of different γ′ rafting microstructures and the initiation of intergranular microcracks in the polycrystalline joint are both studied. [ABSTRACT FROM AUTHOR]

The roles of the alloying elements, Ti and Ta, on the γ' strengthening phase and the corresponding high temperature deformation responses of the CoNi-based superalloys have been systematically investigated. The results indicate that addition of either 4 at.% Ti (4Ti) or 2 at.% Ta (2Ta) can significantly increase the volume fraction of the γ' phase. Detailed analysis of the deformation mechanisms and Gibbs free energies of each phase in the two alloys at elevated temperatures were carried out by using the transmission electron microscopy (TEM) characterization and the thermodynamic calculation, respectively. The dislocations shearing into the γ' precipitates is the primary deformation mechanism in both alloys when deformed at 600 °C. However, when increasing the deformation temperature to 800 °C, the dislocation cross-slipping and by-passing mechanism dominants the 4Ti alloy's deformation, while the additional stacking faults (SFs) were introduced to the 2Ta alloy due to the lower barrier energy of the SFs formation. Continuing increasing the deformation temperature to 1000 °C will promote the dislocation-based mechanisms by lower the dislocation propagation resistance in both alloys. The process will also induce the mechanical twins in the 2Ta alloy which can further strengthening the alloy. The alloying induced deformation mechanism transition and the related high-temperature mechanical performance of the CoNi-based superalloys have been further discussed. • Adding Ti or Ta to the CoNi-based alloy will improve its γ' volume fraction to 60% • Ti and Ta will improve the flow strength at medium and high temperature, respectively • Ta can reduce the energy barrier for stacking fault formation at high temperature • Deformation mechanisms at elevated temperatures can be altered by the alloy elements [ABSTRACT FROM AUTHOR]

Based on its excellent high-temperature performances, polycrystalline Ni 3 Al-based alloys have attracted more and more attention. In this work, different thermal cycle aging treatments (TCAT) were applied to investigate microstructure evolution behavior of Ni 3 Al (γ′) phase in eutectic γ-γ′ area of JG4246A alloy. SEM equipped with energy dispersive X-ray spectrometer (EDS) and high-resolution transmission electron microscopy (HRTEM) were used for microstructure observation and mechanism analysis. The results showed that plate-like Ni 3 Al (γ′) phase and twinning Ni 3 Al (γ′) formed in eutectic γ-γ′ area due to its initial state of the alloy and thermal cyclic aging treatment conditions. Meanwhile, blocky Ni 3 Al (γ′) phase precipitated along eutectic γ-γ′ area and dual phase (γ+γ′) area ((γ-γ′)/(γ+γ′)) interfaces. Vacancies and dislocations generated during short-term TCAT were responsible for the formation of plate-like Ni 3 Al (γ′) phases in eutectic γ-γ′ area of as-cast alloy. While, for the solution-treated alloy, dislocations and internal stress generated during long-term TCAT led to the formation of twinning Ni 3 Al (γ′) in eutectic γ-γ′ area and blocky Ni 3 Al (γ′) phase along (γ-γ′)/(γ+γ′) interface. [ABSTRACT FROM AUTHOR]

The correlation of microstructure-properties of the Ni-based superalloy with coprecipitation of γ'/γ'' phases has been studied in details. To obtain the different γ'/γ'' microstructures, various heat treatments were attempted. The experimental results show that high amounts of the compact γ'/γ'' phases contribute to the tensile strength of Ni-based superalloy, which decreases with the coarsening of γ'/γ'' structures. The γ'/γ'' phases can restrain the motion of the dislocations. Further increasing the size of the γ' and γ'' phases, the deformation mechanism transforms from dislocation pairs shearing to Orowan bypassing, and then to dislocation shearing. Stacking faults (SFs) also appears in γ'/γ'' phases. Additionally, the moderate η/δ phases effectively pin the grain boundary, which enhances the alloy's ductility. [ABSTRACT FROM AUTHOR]

Harsh service environment especially in sulfur-containing atmosphere and complex structures of dominant γ' + γ dendrite, interdendritic region and interface region have significant effect on service life of polycrystalline Ni 3 Al-based superalloys. In this work, hot corrosion behavior of polycrystalline Ni 3 Al-based superalloy in sulfur-containing atmosphere was studied at 900 °C. Growth behaviors of corrosion products were analyzed by X-ray Photoelectron Spectroscopy, Raman spectrometer, Scanning Electron Microscope and Transmission Electron Microscope. The results showed that the growth behaviors of corrosion products were different in different regions. Corrosion products in interdendritic regions were Ni 3 S 2 and Al 2 O 3. While, as for dominant γ' + γ dendrite and interface regions, corrosion products were mainly composed of Ni 3 S 2 , Cr 3 S 4 and mixed oxides. However, though the corrosion products are similar in composition, they have different growth mechanism. Spatial structure and precipitates were observed to analyze and explain the reasons for difference of corrosion behaviors in different regions. • Corrosion behavior of polycrystalline Ni 3 Al-based superalloys was investigated. • Corrosion products are different in different regions. • Elemental distribution and microstructure have significant influence on growth of corrosion products. [ABSTRACT FROM AUTHOR]

A CoNi-based γʹ phase strengthened superalloy was designed with alloy elements Al, W, Cr, Ti, and Ta added. The size and volume fraction of the γʹ phase can be tailored by the post-heat-treatment, which will then affect mechanical behavior of this alloy. The aged alloy was compressively tested at a wide temperature range, from room temperature to 1000 °C. Detailed microstructural analysis of the tested alloy was carried out using transmission electron microscopy. At 600 °C, the primary deformation mechanism is pairs of a/2 <110> type dislocations and stacking faults shearing in the alloy. The deformation mechanism changed to dislocation pile-ups and climbing in the γ phase when deformed at 800 °C. Further increasing the deformation temperature to 1000 °C, both nanotwins and dislocations were formed and their interactions will be the main strengthening mechanism of the alloy. The deformation mechanism transition and correlated mechanical behavior of this alloy was further discussed based on the defect analysis. [ABSTRACT FROM AUTHOR]

A CoNi-based alloy (various cooling rates after solution heat treatment) was utilized to investigate the microstructure-dependent coarsening behavior of γ′ precipitates. The fast cooling rate leads to the formation of initial fine γ′ precipitates with high number density. The different initial microstructures of CoNi-based alloy lead to various coarsening behaviors of γ′ precipitates during subsequent aging treatment at 900 °C. The coarsening behavior of large γ′ precipitates with low density (formed in slow cooling rate, 0.1 °C/s) is in accordance with the Lifshitz-Slyozov-encounter modified (LSEM) model. Whereas for the fine γ′ precipitates with high density (formed in fast cooling rate, 60 °C/s or 240 °C/s), its coarsening behavior is consistent with the TIDC model at early stage and LSEM model at later stage, respectively. • The different initial microstructures of Cobalt-based alloy lead to various coarsening behaviors of γ′ precipitates. • Fast cooling rate leads to the formation of fine γ′ precipitates with high density. • Coarsening of fine γ′ precipitates is consistent with the TIDC model in the early stage and LSEM model in the later stage. • Coarsening of large γ′ precipitates is in accordance with the LSEM model. [ABSTRACT FROM AUTHOR]

The effects of solution cooling rate on microstructure, mechanical properties and the corresponding deformation mechanisms of ATI 718Plus superalloy were investigated. With solution cooling rate decreasing, the volume fraction and the size of primary γ′ phase both increase, which is attributed to that the lower solution cooling rate is beneficial to the migration and interaction of alloy elements in γ′ phase. The tensile strength and microhardness of sample were improved by decrease of solution cooling rate, which is mainly attributed to increase of volume fraction of primary γ′ phase. Specially, the elongation of sample with the lowest solution cooling rate (furnace cooling) was also higher than other samples probably due to large size of primary γ′ phase, which is beneficial to plastic deformation by helping promote active movement of dislocations. In general, three samples exhibit the mixed deformation mechanisms characterized by shearing and bypassing, but primary deformation mechanism of three samples was different, which depends on different precipitation behavior of γ′ phase resulting from different solution cooling rate. The sample that was furnace cooled from solution temperature exhibits a typical shearing deformation mechanism, including stacking faults (SFs) and dislocations shearing, while other two samples with the higher solution cooling rate primarily show an Orowan looping deformation mechanism. The result of calculating critical resolved shear stress (CRSS) exhibits an increasing tendency of SFs shearing while decreasing tendency of Orowan looping with solution cooling rate decreasing, which is corresponding to experimental results. [ABSTRACT FROM AUTHOR]

The isothermal oxidation behavior of micro-regions in multiphase Ni 3 Al-based superalloys (high Fe and Cr contents) was investigated at 600 °C in air. The oxide scale is mainly composed of the outer mixed oxide layer (NiO, NiFe 2 O 4 and Al 2 O 3) and the inner single Al 2 O 3 layer. In particular, Cr 2 O 3 is formed in the outer oxide scale of γ' + γ dendrite with enrichment in Cr element. The relative dense continuous Al 2 O 3 layer is formed in the interdendritic region (β phase with high Al content). In addition, γ' envelope (connecting the γ' + γ dendrite and interdendritic β phase) shows preferential oxidation featuring significant cellular bulge (NiO and NiFe 2 O 4 mixed oxides). Unlabelled Image • The micro-regions in multiphase Ni 3 Al-based superalloy present significant different oxidation behaviors at 600 °C. • The γ' envelope shows preferential oxidization featuring obvious cellular bulge (NiO and NiFe 2 O 4 mixed oxides). • Cr 2 O 3 is formed in the outer oxide layer of γ' + γ dendrite enriching in Cr element. • The dense protective alumina layer is formed on interdendritic region (β phase) with relative high Al content. [ABSTRACT FROM AUTHOR]

The microstructure, element segregation and γ/γ′ interface characters of polycrystalline Ni 3 Al-based superalloys under conventionally solidified (~10 K/s) and rapidly solidified (~103 K/s) conditions were investigated. Cr and Fe are primarily partitioned into the γ phase while Al and Ni are into γ′ phase. However, rapid solidification rate of spray casting alloy improves the solubility of Cr and Fe elements at the expense of Al in γ′ phase, which decreases the lattice parameters of γ and γ′ phases. Moreover, it further increases the absolute value of γ/γ′ lattice misfit and contributes to the formation of (100) plane misfit dislocations in γ/γ′ interface. As a result, spray casting specimen possesses higher hardness (6.5 ± 1.0 GPa) and elastic moduli (166.4 ± 15.9 GPa) than that in as-cast alloy with lower solidification rate. • Rapid solidification rate of spray casting alloy improves the solubility of Cr and Fe elements in γ′ phase. • It further increases the absolute value of γ/γ′ lattice misfit. • The rapidly solidified spray casting alloy possesses high hardness and elastic moduli. [ABSTRACT FROM AUTHOR]

The microstructural evolution and phase transformation behavior of a designed multiphase Ni 3 Al-based superalloy in as-cast and spray casting states were investigated under thermal exposure at various temperatures. For the exposure temperatures range from 600 °C to 900 °C, the average size of γ′ precipitates in the dendritic dual (γ+γ′) areas of the two states alloys increases, and the morphology of γ′ changes to irregular shapes due to merging of neighboring particles and Ostwald ripening. After thermal exposure at 600 °C or 900 °C, bulky γ′ precipitates generate in the interdendritic regions of as-cast alloy, and the γ′ envelope develops a curved interface by aggregation. For the spray casting sample, high density of microtwins in γ′ precipitates are 'inherited' from the preceding L1 0 -type martensite phases after thermal exposure at 600 °C. However, the γ′ precipitates without any microtwins form after thermal exposure at 900 °C. • For as-cast alloy, bulky γ′ precipitates generate in β phase after thermal exposure at 600 °C or 900 °C. • For the spray casting sample, high density of microtwins in γ′ precipitates are 'inherited' after thermal exposure at 600 °C. • The γ′ precipitates without microtwins form in spray casting alloy after thermal exposure at 900°C. [ABSTRACT FROM AUTHOR]

Cyclic oxidation behavior of a polycrystalline Ni 3 Al-based superalloy under as-cast and solution treated conditions was investigated in detail. SEM equipped with energy dispersive X-ray spectrometer and high-resolution transmission electron microscopy was used for microstructure observation and mechanism analysis. Results showed that oxidation process occurred along eutectic area (γ-γ′) and dual phase area (γ+γ′)interfaces firstly for as-cast alloy and oxide scales along (γ-γ′)/(γ+γ′) interfaces spalled gradually with oxidation process proceeding. As for the solution treated alloy, though oxidation process also occurred along (γ-γ′)/(γ+γ′) interfaces, no obvious spalling of oxide scales was observed under the present conditions. Due to the precipitation of Hf-containing carbides which can increase the adhesion of scales and its segregation to Al 2 O 3 grain boundaries during cyclic oxidation to hinder outward migration of Al, leading to slower growth rate of scales. During the long-time (8–200 h) cyclic oxidation process of the solution treated alloy, O atoms continuously diffused towards the matrix along the pores in scales, resulting in thickening of Al 2 O 3 layer. Moreover, thickening of Al 2 O 3 layer also hindered the outward diffusion of Ni and a small amount of NiO was observed on surface of specimen after long-term cyclic oxidation, meaning the improvement of oxidation resistance. • The oxidation behavior occurs on the interface area firstly. • Hf-containing carbides increase the adhesion force of scale. • Solution elements and thermal expansion affect the oxidation behavior. [ABSTRACT FROM AUTHOR]