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Ni-based metallic foams possessing large specific surfaces and open cell structures are of specific interest as catalysts or catalyst carriers for electrolysis of water. Traditional fabrication of Nickel foam limits the element modification choices to several inert transition metals only on polymer foam precursor and subsequent preparation of foam-based catalysts in aqueous solution or organic electrolyte. To expand the modification horizon, molten salt with wide electrochemical window and fast ion diffusion can achieve the reduction of highly active elements. Herein, we reported is a general and facile method to deposit directly of highly reactive element La and prepare hierarchical honeycomb LaNi5 alloy on Ni foam (ho-LaNi5/NF). This self-supporting electrode presents excellent electrical coupling and conductivity between the Ni foam and LaNi5, which provides a 3D self-supported heterostructure with outstanding electrocatalytic activity and excellent durability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). It exhibits excellent overpotential (1.86 V) comparable to commercial coupled IrO2//Pt/C (1.85 V) at a high current density of 100 mA cm−2. This work may pave the way for fabricating novel 3D self-supported honeycomb alloy that can be applied as electrode for usage of clean energy.

The large-scale preparation of monolayer two-dimensional (2D) material remains a great challenge, which hinders its real-world applications. Herein, we report a novel layered metal–organic framewor...

We have proposed and experimentally demonstrated a four-channel wavelength-tunable in-series DFB laser array with 100-GHz channel spacing. Compared to the in-parallel laser array, the optical combiner is not utilized and the extra power loss induced by the combiner is avoided. A linearly chirped Bragg grating with multiple phase shifts implemented in the laser cavity is utilized to reduce the grating interference among different lasers. Besides, the reflector sections are inserted at two ends to provide grating feedback for two side channels. With the feedback, all the channels work with low threshold currents. The linearly chirped Bragg grating requires precise control of grating phase variation, which is quite difficult for traditional e-beam-lithography-based method. Here we used the reconstruction-equivalent-chirp technique to fabricate the grating, and precise control of the grating phase is achieved. From the experimental results, the laser arrays work with high output power (>10 mW), relative intensity noise near the relaxation oscillation frequency of below -130 dB/Hz, stable single-mode operation, and high-uniform channel spacing. Fast channel switchings (

In K4750 alloy, the evolution of grain boundary (GB) precipitates, including the degradation of blocky MC carbide particles and the precipitation of granular/needle-like η phase particles, were observed after long-term aging (LA) at 750°C for 8000 h. During MC degradation, the Ti and C released from the MC carbide combined with Ni and Cr, respectively, in the γ matrix to form η-Ni3Ti phase and Cr-rich M23C6 carbide. Large amounts of granular η phase precipitated at GBs and the needle-like η phase grew gradually from GBs toward the grain interior. Because of the growth of the η phase through absorbing γ′ phase, γ′-depleted zones were formed around the η phase. The evolution of the MC carbide and η phase was primarily responsible for the decrease of the stress rupture life and the increase of elongation. After an LA sample was tested at 750°C and 360 MPa, the residual strain distribution was investigated by electron backscatter diffraction (EBSD). The results showed that the residual strain mainly distributed at GBs, especially in the region of MC degradation and at the edges of η phases, which was closely related to the appearance of phase interfaces. Microvoids/cracks easily initiated at phase interfaces, then easily extended along the γ′-depleted zones, thus the stress rupture life of LA samples was substantially shorter than that of samples subjected to the standard treatment. In particular, because of large amounts of fine degraded MC, granular M23C6 and granular η phase particles distributed at GBs after 750°C /8000 h LA and microvoid/crack formation could be hindered by the formation of dimples, which led to an increase of elongation.

The precipitation characteristics of intergranular carbides generally have a significant impact on the microstructural homogeneity and properties of Alloy 690. M23C6 carbides with distinct dendritic morphology are found precipitating in the continuously cooled Alloy 690, and this study focuses on the effects of solution heat treatment on the morphology evolution of M23C6 carbides during cooling. Results show that if the solution heat treatment is sufficient enough, carbides tend to precipitate in a dendritic morphology during cooling, otherwise rod-like carbides would be dominant on the grain boundary. The precipitation morphology of carbides basically depends on the critical nucleation radius R∗ and the relative supersaturation S which is closely related to the solute concentration on the grain boundary. Insufficient solution annealing will leave undissolved original carbides on the grain boundary, which can grow prior to the precipitation of new carbides and consume lots of solute elements in advance. This earlier solute consumption and the consequent element diffusion could prevent the formation of dendritic carbides, and then rod-like carbides form instead. This study will help to regulate the precipitation morphology of grain boundary carbides in Alloy 690 during continuous cooling, so as to obtain a microstructure conducive to properties.

Fresnel lenses are important compact optical components, which are comprised of multiple faceted concentric rings. These lenses are the most widely utilized diffractive optical element in the industry and has been extensively applied in various optical systems due to their distinct advantages. These include the reduction in the lens thickness, smaller occupied volume and less material required compared to their conventional spherical and aspherical counterparts. In general, the processes to manufacture Fresnel lenses can be categorized into two distinct groups: subtractive fabrication and precision forming. Precision forming processes, like molding and embossing, are usually used in mass production to replicate the optical features and profiles usually employ the use of lens molds generated by subtractive fabrication processes. Thus, the process of molding Fresnel lenses are not substantially different from that of conventional molding processes for other optical components, still relying on the accuracies of the molds utilized. Unfortunately, there is a lack of a comprehensive study to summarize and evaluate the recent advances of UPM techniques to generate these optical Fresnel lens structures. Fresnel lenses and molds differ from each other in terms of lens design, work material and tool/workpiece geometries, and such variations will then drive the development of different machining and characterization methods in terms of tool setting, tool wear, tool path generation as well as lens measurement. This paper summarizes the existing fabrication techniques to generate these lens structures, excluding molding. In addition, a discussion and analysis of the strengths and future areas of research interest of the reviewed techniques are conducted. This review is believed to be helpful and educational for the progress and further development of machining of ultra-precision Fresnel lens structures for advanced optical applications.

This paper underlined the corrosion behavior of aluminum alloy/galvanized steel joints fabricated by resistance spot welding (RSW) and self-piercing riveting (SPR) exposed to different salt-spray cycles. It was found that the crevice generated by different joining methods has an important impact on corrosion behavior. Compared with the RSW joint, less corrosion happened on the coupled regions in SPR joints because of the higher local pH value resulted from the smaller crevice. The crevice, however, has less impact on the types of corrosion products. Galvanic corrosion happened in the coupled region for both RSW and SPR joints. The Pourbaix diagram explained the stable corrosion products of Al and Zn Fe alloy, which are Al2O3, ZnO, and Fe3O4. Additional corrosion products observed from the experiment included α-Al(OH)3, Ca4Al2(CO3)(OH)12(H2O)5, Zn5(OH)8Cl2(H2O), Zn5(CO3)2(OH)6, and Fe2(OH)2(CO3), which can be understood by considering the metastable corrosion products, Pourbaix diagram, and possible chemical reactions.

The effect of reactive element yttrium on purification and carbide precipitation of superalloy K4169 has been studied through vacuum induction melting. The results show that yttrium has a strong deoxidizing and desulfurizing ability, and the impurity elements of sulfur and oxygen in melting K4169 are greatly reduced to 2−5 ppm and 4−5 ppm, respectively. The metallurgical reaction product is mainly Y2O3 and yttrium containing sulfides have not been observed. With the increase of the content of yttrium from 0.005 wt.% to 0.033 wt.%, the morphology and size of MC carbides in casting are significantly influenced due to that the yttrium changes the diffusion of the carbide forming elements and solid fraction during solidification. In the alloys without yttrium, only isolated blocky or strip carbides exist, while skeleton-like carbides are observed in the alloys with yttrium. Both the average size and the number density of skeleton carbides decrease monotonously with yttrium content increasing. After yttrium increasing to 0.033 wt.%, a phase of hexagonal Ni17Y2 is observed to precipitate in the form of symbiosis with MC carbide and matrix. The addition of yttrium is not beneficial for the properties of K4169 alloys at the room temperature, which is quite related to the MC carbides with a large skeleton-like morphology through the analysis of tensile fracture.

In situ growth of pyrochlore iridate thin films has been a long-standing challenge due to the low reactivity of Ir at low temperatures and the vaporization of volatile gas species such as IrO3(g) and IrO2(g) at high temperatures and high PO2. To address this challenge, we combine thermodynamic analysis of the Pr-Ir-O2 system with experimental results from the conventional physical vapor deposition (PVD) technique of co-sputtering. Our results indicate that only high growth temperatures yield films with crystallinity sufficient for utilizing and tailoring the desired topological electronic properties and the in situ synthesis of Pr2Ir2O7 thin films is fettered by the inability to grow with PO2 on the order of 10 Torr at high temperatures, a limitation inherent to the PVD process. Thus, we suggest techniques capable of supplying high partial pressure of key species during deposition, in particular chemical vapor deposition (CVD), as a route to synthesis of Pr2Ir2O7.

In this work, a new preparation method of highly pure gold aerogel using cellulose triacetate as a template was developed. Gold aerogel with high-purity, low density, and elevated specific surface area was successfully prepared by the proposed fast and simple method as a typical example of noble metal aerogels. In this process, the ligament, crystal grain size, and specific surface area of the product could be controlled by adjusting the concentration of the reducing agent. After complete removal of the template, the obtained gold aerogel with 99% purity showed a moderate catalytic effect toward organic pollutants but with great modification potential. The Raman intensity of pure gold aerogel was 3.2-fold higher than that of the conventional porous gold substrate. The excellent effect of the as-prepared nanogold aerogel was attributed to its enhanced surface plasmon resonance effect induced from high purity. In sum, these findings look promising for future application of high-purity gold aerogels in many fields.

Gas tungsten arc welding (GTAW) method was employed to join a newly developed cast superalloy K4750 with Hastelloy X by using K4750 and Hastelloy X filler metals (FMs), respectively. Thereby we obtained two kinds of interfaces namely K4750 base metal (BM) and Hastelloy X FM, and K4750 FM and Hastelloy X BM. The elemental distribution, interfacial characteristics, and the residual welding stress of the dissimilar joints were investigated by electron probe micro analyzer (EPMA), electron backscattered diffraction (EBSD), and section technique, respectively. The results showed that the elemental distribution across both interfaces were varied significantly. And the composition segregation regions were identified in both interfaces but the segregation extent was different. Epitaxial growth was clearly observed in both interfaces. The distribution of the residual welding stress across the joint exhibited that the highest tension stress area in both as-welded joints was located at the joint heat affected zone (HAZ). The residual welding stress in the joint with Hastelloy X FM was significantly relieved through post weld heat treatment (PWHT).

The site occupancy of boron (B) in L12 γ′-Ni3Al and its (010) antiphase boundary (APB) are studied by first-principles calculations in the present work. Based on the electronic structures of the (010) APB, 12 initial tetrahedral sites for B are identified and reduced to 6 distinct configurations due to symmetry, which are transformed into 4 octahedral sites presented by the atomic trajectories during relaxations in first-principles calculations. It is revealed that B atoms prefer to occupy a site far away from the fault layers within the (010) APB of γ′-Ni3Al, agreeing well with previous experimental observations. Bonding charge density is utilized to provide a novel insight into the local L12 → D022 structural phase transformation of the APB and the corresponding tetrahedral-octahedral transition. The energetic site occupation of B is dominated by the lower electron density of the octahedral sites than that of tetrahedral sites.

This study investigated the oxidation behavior of a new casting Ni-based superalloy K4750 at 750 °C-1000 °C in air for 100 h-1000 h by isothermal oxidation tests. The oxidation-kinetic curves were plotted by the static discontinuous weight gain method. Observation and identification of oxidation products were conducted using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD). X-ray photoelectron spectrometer (XPS) was also used to analyze the chemical state of elements and the distribution in depth. The results showed that the oxidation-kinetic curves of K4750 alloy basically obeyed the parabolic law. The average oxidation rate below 900 °C was less than 0.1 g/m2·h which meant the alloy was at a complete anti-oxidation grade, and the alloy was at an anti-oxidation grade at 1000 °C. The predominant surface oxide was Cr2O3, and a double layer structure of the oxide scale was observed at all tested temperatures as time increased. The outer oxide layer contained continuous Cr2O3 and a small amount of oxides mixed TiO2 and NiCr2O4, while the inner oxide layer was composed with Al2O3. The oxidation process could be interpreted by the competitive oxidation of different elements. The diffusion rate of Ti through Cr2O3 layer increased with increasing temperature, and thus the generation of TiO2 was advantageous. The dispersed TiO2 reaching a certain amount destroyed the continuity of the surface oxide layer, which accounted for the reduction of oxidation resistance of K4750 alloy at high temperatures.

The relationship among B content, microstructure evolution and stress rupture properties of K4750 alloy during long-term aging were investigated. After aging at 800 ℃ for 1000 h, the decomposition degree of MC carbides of K4750 alloys with 0B, 0.007 wt. % B and 0.010 wt. % B were basically identical, which indicated that B has no inhibition on MC carbide decomposition during long-term aging. The MC carbide decomposition was accompanied by the formation of M23C6 carbides and a small number of η phases, which was controlled by the outward diffusion of C and Ti combined with the inward diffusion of Ni and Cr from the γ matrix. In addition, M23C6 carbides in boron-free alloy were in continuous chain and needle-like η phases were precipitated near them, while M23C6 carbides in boron-containing alloys remained in granular distribution and no η phases precipitation around them. Adding B could delay the agglomeration and coarsening of M23C6 carbides during long-term aging, which was because the segregation of B at grain boundary retarded the diffusion of alloy elements, thus weakened the local fluctuation of chemical composition near grain boundary. The stress rupture samples of K4750 alloys with various B contents after aging at 800 ℃ for 1000 h were tested at 750 ℃/380 MPa. The results indicated that the stress rupture properties of boron-containing alloys were significantly better than that of boron-free alloy, which could be attributed to the increase of grain boundary cohesion strength and the optimization of M23C6 carbide distribution due to the addition of B.

Gd2Zr2O7 ceramic is considered as one of the most promising host minerals for the immobilization of high-level radioactive wastes. Here, the effects of grain size on the aqueous durability of Gd2Zr2O7 ceramics were studied. Two kinds of leaching experiments were used to research Gd2Zr2O7 ceramic powders and bulks with different grain sizes (5 nm, 78 nm, 1 μm and 18 μm). The results demonstrate that the normalized leaching rates decrease with the increase of grain size. Through characterization and analysis, it is concluded that the hydrolysis reactions of Gd2Zr2O7 occur in the leaching experiment and the hydrolysates are Gd(OH)3 and Zr(OH)4. Besides, all the samples after leaching exhibit slight lattice contraction, which decreases with the increase of crystal grain size. The influence of leaching on the elemental distribution is most significant for the sample with grain size of 5 nm. This study has theoretical guiding significance for the application of Gd2Zr2O7 immobilization.

1Cr15Ni36W3Ti was thermally exposed at 580 ℃ and 680 ℃, respectively, up to 3000 h. The γ’ phase and intergranular TiC carbides continuously coarsened during exposure. None of η, laves or σ phase was discovered in the exposed samples, indicating good microstructure stability under the present exposure conditions. The ripening process of the γ’ phase could be well modelled utilizing the LSW theory. The evolutions of the yield and tensile strengths were monotonous during exposure at 580 ℃. However, a transition point in strengths was detected in the tensile samples exposed at 680 ℃ for 300 h. Accordingly, the critical γ’ diameter was measured to be 13−14 nm. The γ’/dislocations interaction mechanism transformed from shearing to looping with the γ’ diameter exceeding the critical point. The combination of the weakly coupled dislocations model and the Orowan looping model yielded a critical diameter of 13.1 nm which coincided well with the measured one, indicating the applicability of these two strengthening models for 1Cr15Ni36W3Ti. The present exposure conditions did not exert a profound effect on the fracture mode. All the tensile samples underwent a typically ductile fracture with a dimple pattern dominating the fracture surface. The dispersed deformation induced by the prevalence of dislocation looping in the over-aged tensile samples retarded the propagation of intergranular cracks. The declined precipitation hardening increment and the enhanced deformation homogeneity partially recovered the tensile ductility in the over-aged samples exposed at 680 ℃.

Oxygen (O) is an inevitable impurity in bulk metallic glasses (BMGs) and its influence over the glass-forming ability (GFA) of BMGs is a longstanding controversy. The present ab initio molecular dynamics (AIMD) simulations indicate that the GFA decreases upon introducing 0.78 at. pct O in the amorphous Zr55Cu55Al9Be9 (at. pct), while examining the evolution of atomic configurations and kinetic properties in BMGs. This study includes a comprehensive analysis using pair correlation function (PCF), bond pair analysis (BPA), and Voronoi polyhedra construction. It is concluded that the incorporation of O leads to a decline in the closely packed icosahedral polyhedrons, where the atom O is coordinated with Be and Zr in the first nearest shell to form the O-centered clusters with enhanced ordering. Mean square displacement (MSD) analysis also shows that the trace O could induce remarkable acceleration of atomic mobility, therefore increasing crystallization tendency of the Zr55Cu55Al9Be9 alloy. The present results illuminate the role of O in the metallic glass-forming process and reveal the underlying role of O in the GFA of the Zr-Cu amorphous alloys.

As technological components continue to utilize space effectively within devices without compromise to their operational efficiency, the relevance of accurate and precise parts with good tolerances and surface finishing has shot to prominence. Ultra-Precision Machining (UPM) technology has constantly risen to the challenge by realizing components with superior geometrical accuracies and mirror-like surface finishes, much of which are required in the optical industry. However, conventional diamond shaping processes are usually limited to rotary symmetric components or linear gratings. Thus, the developed Virtual Rotating Tool Shaping (VRTS) addresses these issues by enabling the UPM to fabricate non-rotary symmetric, intricate and freeform elements by Direct Diamond Shaping (DDS). VRTS synchronizes the linear and rotational motions of the ultra-precision machine to constantly align the tool with the cutting direction, while compensating in the linear axes for the run-off. As such, DDS can now achieve a combination of linear and rotary features by planing. In this paper, the developed DDS technique is presented with experimental verifications of the algorithm on a segmented bi-focal Fresnel lens and a serpentine micro-channel, followed by the corresponding analyses.

Tensile properties at room temperature of a new casting Ni-base superalloy during aging at 800 °C for 0-1000 h were investigated. During aging, granular M23C6 carbides presented at grain boundaries and kept growing from dispersed particles to continuous networks. The γ′ phase significantly coarsened, with the morphology of some γ′ phase changed from spherical to rounded cubic shape after 1000 h. Three deformation mechanisms in relation to the γ′ diameter (dγ′) were identified: (i) weakly coupled dislocations (WCD) connected by anti-phase boundary (APB) traveled in pair across the γ/γ′ structure when dγ′ was small in the under-aged alloys; (ii) strongly coupled dislocations (SCD) with reduced spacing compared to (i) sheared γ′ phase when dγ′ increased in the over-aged alloys; (iii) dislocations occasionally by-passed γ′ phase when dγ′ was larger than 97 nm after aging for more than 300 h. The alloy obtained the peak strength when 20 h-aged with dγ′ = 44 nm which was in the transition between (i) and (ii). The aging-induced variation in yield strength was correlated to the coarsening of γʹ phase using a theoretical model of precipitation strengthening in terms of the formation of APB. The calculated results suggested that the γ′ phase with a volume fraction of 23% contributed more than 61% of the peak-aged yield strength. Observation after fracture revealed that the alloys usually fractured at grain boundaries. High stress concentration around carbides resulted in cracks by carbides self-cracking and the initiation of cavities. The undesirable agglomeration of M23C6 at grain boundaries was harmful to the properties of the over-aged alloys.

In this study, a series of transparent ceramics with chemical composition of La1+xYb1+yZr2O7 (x, y = 0.1−0.5) were successfully prepared by vacuum sintering using combustion synthesized powders. The effects of excess contents on the phase composition, microstructure and in-line transmittance have been studied. The detailed results indicate that the in-line transmittance increases at first and then decreases as La content be elevated. It was also determined that the highest in-line transmittance of La1+xYb1+yZr2O7 (x, y = 0.1−0.5) ceramics is 84.1 % at 1100 nm when the excess amount of co-doped La-Yb is 30 %. Compared with stoichiometric LaYbZr2O7 ceramic, the nonstoichiometric La1+xYb1+yZr2O7 (x, y = 0.1−0.5) ceramics exhibit much higher transparency. In addition, the high excess amount of La, Yb and co-doped La-Yb also shows effects on the phase composition and crystal structure.

Interfacial reactions of various cold isostatic pressed oxide crucibles (calcia, yttria-stabilized zirconia, and yttria) with Ti–5wt% Cu alloy at 1680 °C for 15 min melting in an argon environment have been investigated to estimate the corrosion resistance. Predicting thermodynamic analysis results indicate that oxide refractories based on calcia, zirconia, and yttria, can be used for melting titanium–copper alloy. However, significant differences between experimental results and those thermodynamic analysis results in the ZrO2–12 wt% Y2O3 and CaO systems were identified. The surface observations and element distribution made on cross-sections perpendicular to the interface using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) show that obvious interfacial reactions between alloy melt and ceramics in ZrO2–12 wt% Y2O3, and CaO systems occur at experimental temperature, while yttria shows the most superior stability with the most desirable features of interface properties of metal and crucible, and the product of dissolved Y2O3 was still found in the metal. Meanwhile, the interaction between the ZrO2 oxide and the Ti–5 wt% Cu melt can be effectively reduced by the addition of Y2O3. The high apparent porosity of the crucible results in low resistance to erosion caused by Ti–5Cu melt. Moreover, the reduction of calcia causes the boiling of the melt. These results would provide the basis for designing a new refractory for the melting of titanium–copper alloy.

Based on the growing power of computational capabilities and algorithmic developments, with the help of data-driven and high-throughput calculations, a new paradigm accelerating materials discovery, design and optimization is emerging. Titanium (Ti) alloys have been chosen herein to highlight an integrated computational materials engineering case study with the aim of improving their strength and ductility. The electronic properties of elemental building blocks were derived from high-throughput first-principles calculations and presented in the form of the Mendeleev periodic table, including their electron work function (Ф), Fermi energy (EF), bonding charge density (Δρ), and lattice distortion energy. The atomic and electronic insights of the composition–structure–property relationships were revealed by a data mining approach, addressing the key features/principles for the design strategies of advanced alloys. Guided by defect engineering, the deformation fault energy and dislocation width were treated as the dominating criteria in improving the ductility. The proposed yield strength model was utilized quantitatively to present the contributions of solid-solution strengthening and grain refinement hardening. Machine learning was used collaboratively with fundamental knowledge and feed back into a new training model, shown to be superior to the empirical molybdenum equivalence method. The results draw a conclusion that the integration of data mining and machine learning will not only generate plausible explanations and address new hypotheses, but also enable the design of strong and ductile Ti alloys in a more efficient and cost-effective way.

Atomic structure, diffusivity and viscosity of Al1-xMgx (x=0, 0.0039, 0.1172, 0.9180, 0.9961, 1)melts at 875, 1000, 1125, and 1250K were investigated by the ab initio molecular dynamics (AIMD) simulations. The simulated results are compared with available experimental and calculated data in the literature with reasonable agreements. Considering the results of pair correlation function g(r), it can be observed that Mg atoms in Al0.8828Mg0.1172 melt aggregate more obviously at 1000 and 1250K. For Al0.0820Mg0.9180, Al atom segregation is more obvious at 875 and 1000K. The tracer diffusion coefficients of Al or Mg in Al1-xMgx (x=0.1172, 0.9180) melts, and interdiffusion coefficients of Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts are all close to the self-diffusion coefficients of Al or Mg. With the increasing temperature, the diffusivity increases linearly. In dilute melts, the tracer diffusion coefficients of solute atom and the interdiffusion coefficients increase nonlinearly with the increasing temperature. For Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts, the viscosities ? are comparatively higher than pure melts. The viscosities of all melts decrease with the increasing temperature, then increase at 1250K. The results obtained in the present work provide an insight into the design of Al and Mg alloys.

To study quantitatively the effect of heat treatment on the microstructure, composition and mechanical property in a new single crystal nickel-based superalloy for industrial gas turbine (IGT) applications, the eutectic fraction, carbide fraction, and the fraction, size, shape and distribution of the γ ́ phase was characterized by quantitative metallographic method, the evolution of chemical composition and hardness between core and inter dendrite was tested through EMPA and nanoindentation. The experimental results indicate that: The eutectic fraction decreases from (0.52±0.08) % to (0.03±0.01) %. The carbides fraction decreases from (0.23±0.04) % to (0.12±0.03) %, and Feret ratio decreases from 3.21±2.54 to 2.14±0.98. The γ ́ fraction increases from (55.66±4.18) % to (73.78±3.24) % in core dendritic region, from (64.82±1.44) % to (70.11±3.10) % in inter dendritic region. The γ ́-size is 406±111(nm) in core dendritic region and 918±384(nm) in inter dendritic region before heat treatment, 359±69(nm) in core dendritic region and 361±57(nm) in inter dendritic region after heat treatment. The γ ́-cuboidal degree is 1.08±0.20 in core dendritic region and 1.14±0.23 in inter dendritic region before heat treatment, 1.08±0.19 in core dendritic region and 1.02±0.14 in inter dendritic region after heat treatment. The solidification segregation coefficient of main segregation elements, such as Re, W, Hf, Ta, Al, and Mo, is closer to 1, with an average decrease of 27% after heat treatment. The hardness and modulus increase in core and inter dendritic, and their inhomogeneity is reduced between cores and inter dendritic. The improvement of properties result from the improvement of size uniformity and cuboidal degree of γ ́, and the reduction of carbides and eutectic through element homogeneity during heat treatment. The solidification segregation coefficient of main segregation elements, such as Re, W, Hf, Ta, Al, and Mo, is closer to 1, with an average decrease of 27% after heat treatment. With the addition of refractory elements, some elements partition to the dendrite core, while other elements tend to accumulate in the interdendritic liquid and then solidify as the interdendritic and eutectic regions during solidification. The hardness and modulus increase in core and inter dendritic, and their inhomogeneity is reduced between cores and inter dendritic. The improvement of properties result from the improvement of size uniformity and cuboidal degree of γ ́, and the reduction of carbides and eutectic through element homogeneity during heat treatment.

The effect of boron addition at 0, 0.007 wt. % and 0.010 wt. % on the microstructure and mechanical properties of K4750 nickel-based superalloy was studied. The microstructure of the as-cast and heat-treated alloys was analyzed by SEM, EPMA, SIMS and TEM. Lamellar M5B3-type borides were observed in boron-containing as-cast alloys. After the full heat treatment, boron atoms released from the decomposition of M5B3 borides were segregated at grain boundaries, which inhibited the growth and agglomeration of M23C6 carbides. Therefore, the M23C6 carbides along grain boundaries were granular in boron-containing alloys, while those were continuous in boron-free alloys. The mechanical property analysis indicated that the addition of boron significantly improved the tensile ductility at room temperature and stress rupture properties at 750 ℃/430 MPa of K4750 alloy. The low tensile ductility at room temperature of 0B alloy was attributed to continuous M23C6 carbides leaded to stress concentration, which provided a favorable location for crack nucleation and propagation. The improvement of the stress rupture properties of boron-containing alloys was the result of the combination of boron segregation increased the cohesion of grain boundaries and granular M23C6 carbides suppressed the link-up and extension of micro-cracks.

The role of C on microstructure and local chemical composition of an as-cast Ti42Al5Mn alloy was systematically characterised. Results show that C is enriched in α2, less dissolved in γ but deplete...

It is known that there are some grinding issues for difficult-to-machine materials, such as adhesion of the grinding wheel, grinding burns, and poor surface quality. In this work, a novel abrasive ...

To verify the microalloying function and segregation behavior of trace Mg at grain boundary in steel, the 2.25Cr–1Mo steel doped with 0.056% P containing different Mg contents was refined with a vacuum-induction furnace. The effects of trace Mg addition on the temper embrittlement susceptibility of 2.25Cr–1Mo steel were studied by step-cooling test and the segregation behavior of Mg at grain boundary was explored by Auger electron spectroscopy. It is shown that P-induced temper embrittlement susceptibility can be reduced after subjecting to step-cooling treatment with trace Mg addition, mainly benefited from the segregation of Mg at grain boundary. This segregation can decrease the segregation amounts of P and S, especially for P, and increase the grain boundary cohesion, reducing the adverse effect on temper embrittlement caused by P and S.

Thermodynamics is a science concerning the state of a system, whether it is stable, metastable or unstable, when interacting with the surroundings. In this overview, fundamentals of thermodynamics are briefly reviewed through the combination of first and second laws of thermodynamics for open and nonequilibrium systems to demonstrate that the reversible equilibrium and irreversible nonequilibrium thermodynamics can be integrated to enhance the power and utilities of thermodynamics. The recent progresses in computational thermodynamics, the remaining challenges, and potential impacts in broad scientific fields are discussed. It is shown that computational thermodynamics enables the modeling of thermodynamics of a state as a function of both external and internal variables and quantitative calculations of a broad range of properties of a multicomponent system in terms of first and second derivatives of energy, including not only equilibrium states when there are no driving forces for any internal processes and but also non-equilibrium states with driving forces for internal processes. Consequently, external constraints such as fixed strain and internal degree of freedoms such as ordering and defects can be described in a coherent framework and applied to materials design. Furthermore, two important but largely overlooked aspects in thermodynamics will be discussed, i.e. the rigorous application of statistical thermodynamics with the probability of configurations and their contributions to system properties, and the applications of second derivatives of energy with respect to either two extensive variables or two potentials or a mixture of them in terms of understanding and predicting emergent behaviors, critical phenomena, kinetic coefficients, and mechanical properties.

Multi-wavelength distributed feedback laser array based tunable semiconductor lasers have been widely used owing to their high mode stability and simple tuning scheme. Comparing with the in-parallel laser array, the in-series one can avoid a large power loss caused by the optical combiner. However, the single-mode stability of an in-series laser array is vulnerable to the reflections of other lasers. Here we experimentally demonstrated a tunable in-series laser array with high single-mode stability and high uniformity of wavelength spacing. To reduce the impact of such reflections, the Bragg gratings in different lasers were designed in phase, and the grating phase error was reduced by utilizing the reconstruction-equivalent-chirp technique. Besides, a three-section laser structure was applied in each laser to increase the priority of the dominant lasing mode. Four lasers with small wavelength-spacings of 2.5 nm were integrated in the in-series laser array. According to the measurement results of 40 in-series laser arrays (160 lasers), wavelength deviations of 90.6% lasers were within ±0.2 nm, average wavelength spacings of 97.5% of the measured laser arrays were deviated from the design within ±0.2 nm, and SMSRs of 96.3% lasers were above 45 dB. The output power was above 25 mW and the relative intensity noise was below −130 dB/Hz. Like the in-parallel laser array, the proposed laser array can be applied in either continuous wavelength tuning or fast channel switching. For the continuous wavelength tuning applications, the 10-nm tuning range was obtained with a temperature tuning range of less than 20 °C. For the fast channel switching applications, four channels with 2.5-nm spacing are available, and the switching time between two channels was less than 300 ns.

Ultra-precision machining has been well known as a very precise and effective way to prototype and fabricate different types of components with microstructures. In this paper, an ultra-precision micro-milling method has been presented to produce a micro-step pillar array as an embossing mold for semiconductor application. Theoretical analysis on machining mechanics indicates that work material property, machining strategy, and cutting tool geometry largely affect machining distortion on the machined microstructure. Experimental investigation has been conducted on micromachining of the micro-step pillar array using different types of cutting tools and work materials. Experimental results demonstrate that the material property, cutting tool edge radius, and cutting force play a significant role in the machined micro-structure accuracy and surface finish, while grain boundary of brass has no significant effect on the micro-milling performance. The best outcome among the tests done is achieved when using brass as work material and cutting with a straight-edge single crystalline diamond tool. The main reasons to achieve this outcome are based on: the brass material having a higher elastic modulus and the diamond tool having a smaller cutting edge radius, which contributes to better machinability of brass. One micro-step pillar array has been successfully obtained with very precise feature and dimensional accuracy using brass work material and single-crystal diamond tool. It is believed that the outcomes of this study would largely benefit the research community and end-users.

The precipitation behavior of different phases in a high-silicon stainless steel (6 wt% Si) during aging at 600–1050 °C for 24 h was investigated. The morphology, crystal structure and composition of various precipitates were detailly characterized using optical microscopy, scanning electron microscopy and transmission electron microscopy. Four phases were mainly identified: χ-phase, M6C carbides, σ phase and a new type of fcc-phase. During aging at 600–900 °C, the main precipitate was (Cr, Mo and Si)-rich χ-phase which was directly precipitated from γ matrix. The χ-phase was calibrated as bcc structure with a lattice parameter of 8.90 A. The peak temperature for the precipitation of χ-phase was 800 °C, and it was dissolved when aging at temperatures above 1000 °C. The σ-phase was observed only at 700 °C and grew next to χ-phase. Above 700 °C, a new fcc-phase was found to be precipitated along with χ-phase, with a space group of Fd3c and a lattice parameter of 12.56 A. The M6C carbides started to be precipitated at 700 °C in the vicinity of χ-phase. And its amount basically increased with the increasing of temperature. An orientation relationship between M6C/γ was found: [100]c//[100]γ, (001)c//(001)γ, i.e., the cube-on-cube relationship.

Potassium-ion batteries (PIBs) have attracted great interest due to their high-energy-density and low-cost. The lack of stable anode material greatly limits the quick development of PIBs. Phosphorus-metal compounds are regarded as a class of materials with promising prospects as anode material for PIBs with a low operating voltage and high conductivity. Among them, due to the challenging synthesis method, the application of SnP is limited. Herein, a facile approach to synthesize trigonal SnP@C through alloying red phosphorus with tin on carbon material is reported. It is found that carbon substrate can largely reduce vibrational and configurational entropies, playing a critical role on the formation of metastable SnP. When applied as anode in PIBs, the SnP@C composite delivers a high reversible capacity of 478.1 mAh·g−1 at 50 mA g−1 and a stable cycling performance at 1000 mA g−1. The good electrochemical performance is associated with the SnP@C as well as the carbon, which could suppress the phase separation during charge/discharge process to maintain structural stability. This work may open a new avenue for low-cost synthesis of metastable phases for advanced energy storage systems.

Overcoming the myriad challenges in the high-speed machining of Inconel 718, especially for deep-hole drilling (DHD), has been a long-standing area of research for several manufacturers and researchers. Owning to the difficult-to-machine characteristics of Inconel 718, the traditional carbide-tipped gun drills often get worn at an accelerated pace and require repetitive re-sharpening or replacement. This lowers productivity and increases costs. Furthermore, it is also a challenging task to meet the stringent hole-straightness requirement of 1/1000 mm for DHD of such difficult-to-machine materials, especially using those carbide gun drills. Hence, this study presents a development of polycrystalline cubic boron nitride (PCBN)-tipped gun drill to address the rapid tool degradation and poor hole-straightness issues. The developed PCBN-tipped gun drill has a layer of PCBN on its cutting tip and bearing pads. Several gun drilling tests on Inconel 718 have been performed at high drilling speed conditions to assess the performance of developed gun drill. In contrast to traditional carbide-tipped gun drills, the developed PCBN-tipped gun drill has the capability of not only performing in the higher cutting speeds but also reducing drilling forces, drilling torques, and tool wear. Furthermore, the surface quality of drilled holes is also much better than those drilled by traditional carbide gun drills. With these results, it further validates the credibility of the developed PCBN gun drill in enhancing the deep-hole drilling process with high throughput productivity and superior quality of drilled holes, especially for difficult-to-machine materials.

Using ab initio density functional approach, we analyze the trapping behavior of Hydrogen atom in a series fcc structure metals (M = Ni, Cu and Al). From the calculations we found that the potential trapping sites in all these three metals is strongly correlated with the electron charges distribution and the swelling of the nH-Vac cluster is largely determined by the transferring charges of the metal atoms around the vacancy. According to our results, in both intrinsic metals and the metal with monovacancy the hydrogen atoms are always prone to be trapped at the interstitial site with large pre-existed charges and the growth of nH-Vac cluster greatly depends on the charges supplying by the surrounding metal atoms. By our calculations the deficit charges supplying by the nearby metal atoms always accompany a strain energy increment which forbid the nH-Vac swelling. This mechanism is identified in all these three fcc metals. We also found that the formation of hydrogen molecule at the center of the vacancy can only be identified in Aluminum no matter the trapping sites around the vacancy are fully occupied or not. But in Ni and Cu with the same fcc structure H2 molecule are not popular.

Metallic amorphous/crystalline (A/C) nanolaminates exhibit excellent ductility while retaining their high strength. However, the underlying physical mechanisms and the resultant structural changes during plastic deformation still remain unclear. In the present work, the structure-property relationship of CuZr/Cu A/C nanolaminates is established through integrated high-throughput micro-compression tests and molecular dynamics simulations together with high-resolution transmission electron microcopy. The serrated flow of nanolaminates results from the formation of hexagonal-close-packed (HCP)-type stacking faults and twins inside the face-centered-cubic (FCC) Cu nano-grains, the body-centered-cubic (BCC)-type ordering at their grain boundaries, and the crystallization of the amorphous CuZr layers. The serration behavior of CuZr/Cu A/C nanolaminates is determined by several factors, including the formation of dense dislocation networks from the multiplication of initial dislocations that formed after yielding, weak-spots-related configurational-transitions and shear-transition-zone activities, and deformation-induced devitrification. The present work provides an insight into the heterogeneous deformation mechanism of A/C nanolaminates at the atomic scale, and mechanistic base for the microstructural design of self-toughening metallic-glass (MG)-based composites and A/C nanolaminates.

Cutting performance and failure mechanisms of spark plasma sintered (SPS) ultrafine cemented carbides in dry turning Ti–6Al–4V were studied. The tools of UYG8 (WC-8wt%Co) and UYG8V2B10 (WC-8wt%Co-0.2 wt%VC-1.0 wt%cBN) exhibited higher lifetime and better processing quality than the commercial YG8 cemented carbide tool. The cutting distance of UYG-8 and UYG8V2B10 tools are 1.8 and 1.6 times longer than that of YG8, respectively. Cutting-edge breakage was found as the main failure forms of the SPS cemented carbide tools containing low Co content (≤6 wt%), whereas the SPS cemented carbide tools containing high Co content (≥8 wt%) exhibited flank and rake wear as main failure forms caused by abrasion, adhesion, diffusion, and oxidation. UYG8V2B10 tool wear mechanism was affected by cutting speed and depth. Wear mechanisms of UYG8V2B10 tool are mainly adhesive wear and oxidative wear at low cutting speed, but follow adhesive wear and diffusive wear at higher cutting speed. Moreover, with increasing cutting depth, tool failure forms are mainly breakage and chipping, largely induced by high cutting temperature and severe cutting vibration.

Effects of silicon on the microstructure and mechanical properties of 20% cold-worked 15–15Ti austenitic stainless steels are systemically investigated by uniaxial tensile tests, scanning and transmission electron microscope observations, and strength calculations. The results reveal that a large number of deformation twins are formed in the 20% cold-worked steels with various silicon additions. The volume fraction of deformation twins and the density of dislocations increase with silicon content, while the twin thickness slightly decreases. A better strength–ductility combination is achieved by silicon addition, since the yield strength of the steel with 2% silicon is 61 MPa higher than that of the steel with 1% silicon, while their uniform elongations are almost both equal to 16%. The yield strength of the 15–15Ti stainless steels is predominantly contributed by the solid solution, dislocation and deformation twin strengthening effects, which can be enhanced by silicon addition.

Gd2Zr2O7 ceramics demonstrate important prospect in the immobilization of high-level radioactive wastes (HLWs). In this study, Gd2Zr2O7 nanoceramics were fabricated using two-step method, where Gd2Zr2O7 nanopowder was firstly synthesized by solvothermal method and Gd2Zr2O7 nanoceramics were subsequently sintered via self-propagating chemical furnace plus quick pressing (SCF/QP). The characterization results display that the Gd2Zr2O7 nanocrystalline ceramics with average grain size of 78 nm and bulk density of 5.53 g cm−3 were successfully prepared. The results of MCC-1 static leaching experiments show that the normalized release rate (LRi) of Gd is 2.2 × 10−2 g m−2•d−1 on the first day and converges to 1.2 × 10−3 g m−2•d−1 after 42 days. Zr shows superior chemical stability as the 21 days LRZr value is as low as 2.7 × 10−6 g m−2•d−1, which becomes constant as the leaching duration prolongs.

Microstructural non-uniformity in the wrought material of Alloy 690 is investigated in this study by analyzing the dissolution behavior of intergranular carbides, performing laboratorial forgings to explore the microstructural evolution rules and conduct industrial forgings to verify the laboratorial results. The intergranular carbides in Alloy 690 ESR ingots cannot be fully dissolved at a temperature

s Fictive associates are widely used to describe and model liquid phases with strong ordering trends. However, little evidence is known about the assumed associates in most cases. In the present work, an ab initio molecular dynamics (AIMD) study is employed to investigate the characters of the Ba-Bi liquid, in which associates have been assumed in existing thermodynamic modeling. It is found that in the Ba rich melt, the Bi atoms are almost completely surrounded by Ba atoms. The Bi-centered coordination polyhedrons are strongly associated to crystalline structures of Ba5Bi3 and Ba4Bi3 with a longer lifetime than other polyhedrons during the AIMD simulations. In addition, these Bi-centered polyhedrons in Ba rich melt connect with each other through vertex, edge, face, and/or bipyramid sharing to form medium range orders (MRO). In the Bi rich melt, the Ba-centered polyhedrons also form MROs, but they are both structurally and compositionally diverse with a shorter lifetime. These findings from AIMD study provide evidences that there exist a strongly ordering Ba4Bi3 associate and a weakly ordering BaBi3 associate in the Ba-Bi liquid. The predicted enthalpy of mixing in the liquid agrees well with the results by the CALPHAD modeling in the literature.

TiAl-based alloys containing relatively high Mn (e.g., Ti–42Al–5Mn (in at.%)) possess excellent hot workability and cost-effective advantages, but may also have poor oxidation resistance at high temperature. Hence, additional attention needs to be paid on the oxidation resistance of these alloys. In this study, a Mn-containing γ-TiAl-based alloy with the composition of Ti–42Al–5Mn has been chosen, and the oxidation behavior of this alloy with different W additions under thermal cycling conditions at 800 °C was investigated. The morphology and the composition distribution of the oxide scale were analyzed by means of scanning electron microscopy equipped with energy-dispersive spectroscopy, X-ray diffractometry and X-ray photoelectron spectroscopy. Auger electron spectroscopy depth profiling was used to investigate the effect of W on the initial stage of oxidation. It shows that the addition of 1 (at.%) W can significantly reduce the oxidation mass gain, and the oxidation reaction rate constant is decreased by an order of magnitude. The adherence of oxide scale is greatly enhanced with no spallation observed in Ti–42Al–5Mn–(0.8, 1)W after 100-h cyclic oxidation. Tungsten promotes the selective oxidation of Al and formation of a denser oxide scale which prevents the inward diffusion of oxygen; in this way, high-temperature oxidation resistance of the alloy is improved.

Ultrafine-grained tungsten carbide-cobalt (WC-Co) cemented carbides with different Co content were fabricated by spark plasma sintering. Then, tribological behavior of the ultrafine-grained WC-Co cemented carbides were studied by performing sliding wear tests with grinding balls made of GCr15 bearing steel (HRC 62∼66) and Ti-6Al-4V titanium alloy (HRC 36). When the grinding ball is composed of GCr15 steel, the time required to reach the stable friction stage decreases with the increase in cobalt content, whereas the friction coefficient and wear rate tend to increase, and the wear type is abrasive wear. When the grinding ball is made of titanium alloy, the friction coefficient and adhesive wear volume first increase and then decrease with the increase in Co content, both reaching maximum values at 6 wt.% Co, and the wear type is adhesive wear.

This article presents a brief review of our case studies of data-driven Integrated Computational Materials Engineering (ICME) for intelligently discovering advanced structural metal materials, including light-weight materials (Ti, Mg, and Al alloys), refractory high-entropy alloys, and superalloys. The basic bonding in terms of topology and electronic structures is recommended to be considered as the building blocks/units constructing the microstructures of advanced materials. It is highlighted that the bonding charge density could not only provide an atomic and electronic insight into the physical nature of chemical bond of materials but also reveal the fundamental strengthening/embrittlement mechanisms and the local phase transformations of planar defects, paving a path in accelerating the development of advanced metal materials via interfacial engineering. Perspectives on the knowledge-based modeling/simulations, machine-learning knowledge base, platform, and next-generation workforce for sustainable ecosystem of ICME are highlighted, thus to call for more duty on the developments of advanced structural metal materials and enhancement of research productivity and collaboration.

Al-Co-Cr-Fe-Ni alloys have been modelled by computational thermodynamics according to the CALPHAD approach using literature data and results of a few key experiments performed in this work. As a result, an Al-Co-Cr-Fe-Ni thermodynamic database has been developed, based on the thermodynamic assessments of all the binary and ternary subsystems and the addition of a few quaternary interaction parameters. The assessment was supported by ESPEI (Extensible Self-optimizing Phase Equilibria Infrastructure), a tool for thermodynamic database development within the CALPHAD method. Computed phase equilibria in the quinary system are in good agreement with experimental data from the literature and the present experiments.

WC-Co cemented carbide tools offer better cutting performance when cutting difficult-to-machine materials, such as high-temperature alloys, titanium alloys, and high-strength steels. In this paper, high performance WC-8 wt.% Co cemented carbide materials with cBN and VC were prepared by spark plasma sintering. The effects of cBN and VC content on mechanical properties and microstructure of WC-8 wt.% Co-VC-cBN cemented carbide materials were studied. The results show that the relative density, Vickers hardness, and fracture toughness of WC-based cemented carbide materials decreased significantly as the content of cBN and VC increased. WC-8 wt.% Co-0.2 wt%VC-1 wt.% cBN (named as YG8V2B10) cemented carbide material had the optimal properties when sintered at 1250 °C. Its Vickers hardness, fracture toughness, and flexural strength are 20.81 GPa, 13.01 MPa m1/2, and 1630 MPa, respectively. High-temperature flexural strength of YG8V2B10 was also investigated. The flexural strength of YG8V2B10 cemented carbide materials decreased as the temperature increased. When the temperature of YG8V2B10 cemented carbide material exceeded 400 °C in air, matrix at the surface of YG8V2B10 was oxidized, which leads to a significant decrease in the flexural strength.