A new design of seamless joining was proposed to join SiC using electric field-assisted sintering technology. A 500 nm Y coating on SiC was used as the initial joining filler to obtain a desired ...transition phase of Y3Si2C2 layer via the appropriate interface reactions with the SiC matrix. The phase transformation and decomposition of the transition phase of Y3Si2C2 was designed to achieve almost seamless joining of SiC. The decomposition of the joining layer to SiC, followed up by the inter-diffusion and complete densification with the initial SiC matrix, resulted in the formation of an almost seamless joint at the temperature of 1900 °C. The bending strength of the seamless joint was 134.8 ± 2.1 MPa, which was comparable to the strength of the SiC matrix. The proposed design of seamless joining could potentially be applied for joining of SiC-based ceramic matrix composites with RE3Si2C2 as the joining layer.
Designing single-phase ceramics with favorable self-lubricity is a substantial challenge due to the strong chemical bonds and difficulty to shearing. Most conventional lubricating ceramics only ...benefit from adding solid lubricants, which largely limits the mechanical properties of the resulting materials. Here, we report a single-phase ceramic inspired by the novel high-entropy design concept and tribo-induced effect, and which can achieve an outstanding self-lubricity (friction coefficient is as low as 0.1) at 200–400 °C in a vacuum environment. The self-lubricity is attributed to two factors, namely the decomposition of the (Hf-Mo-Nb-Ta-Ti)C ceramic leading to formation of the amorphous carbon film at the sliding interfaces, and the diffusion of carbon atom under the effect of high-temperature tribo-induced enabling easy shear contact. Based on the experimental and theoretical findings, we formulate a novel design strategy for single-phase self-lubricating ceramics by in-situ forming lubricating phase.
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•A detailed thermodynamic dataset of the Al-Ni-Si-Y system is established.•The phase constitutions significantly change with varying contents of Al or Si.•The Ni5Y phase is always ...precipitated in the NiSiAlY alloys.•A very narrow composition range of the NiSiAlY alloys is proposed.•The description can help to design novel NiSiAlY alloys for different usage.
The NiSiAlY material is a promising candidate to replace NiCrAlY, which can withstand the harsh salt-spray conditions in marine environment. To efficiently design novel NiSiAlY alloys, this work establishes a thermodynamic dataset of the Al-Ni-Si-Y quaternary system using the CALPHAD (CALculation of PHAse Diagrams) approach. We employ this database to calculate and predict the phase constitutions and solidification behaviors of different NiSiAlY alloys concerning the content variations of Al and Si. We have further proposed the selection of the NiSiAlY alloys for serving in marine salt-spray environment with three constraints: (i) outstanding mechanical property; (ii) good high-temperature anti-oxidation; (iii) excellent corrosion resistance. This results in a compositional range of the NiSiAlY alloys with 1 wt% <w(Si) < 5 wt%, 11 wt% <w(Al) < 20 wt% and w(Y) =1 wt%, which corresponds the L12+bcc_B2+Ni5Y ternary phase region at temperatures ranging from ∼500 to ∼1000 °C. Our predictions are validated by key experiments, suggesting that the model-based description of the Al-Ni-Si-Y system can serve as a guidance to design the novel NiSiAlY alloys in resisting harsh salt-spray environment.
TiO2 is a highly promising anode material for lithium-ion batteries with a high rate and long-term cycle performance. However, it exhibits a frustrating conductivity, similar to other oxide ...electrodes, along with triggered poorer rate and long cycle performance. Herein, a strategy combining atomic substitution and nanoengineering is proposed for the preparation of Ti1-xSnxO2 solid solution hollow spheres. Not only the electrochemical properties are modulated but also the electrochemical mechanisms are further considered. As a result, the Ti0·85Sn0·15O2 electrode achieves superior rate and cycling properties, achieving a specific capacity of 178.5 mAh g−1 at current densities up to 20 C (1 C = 335 mA g−1), maintaining 314.6 mAh g−1 after 1100 cycles at 3 C and 129.1 mAh g−1 after 1500 cycles at 10 C. Theoretical simulations and experimental investigations reveal that Ti1-xSnxO2 electrochemical phase separation, not an atomic substitution, is an indispensable factor in enhancing electrochemical properties. Ti1-xSnxO2 electrochemical phase separation to build TiO2/SnO2 heterojunctions, modulating the electronic structure near the Fermi energy level to enhance electrical conductivity and reduce Li+ migration energy barriers. This work on the optimization of electrochemical properties and electrochemical mechanisms will facilitate the promotion of the development of advanced energy storage systems.
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Herein, the γ(Ni)/γ’(Ni3Al) duplex phase binders were introduced into the Ti(C, N)-based cermets, with their wear behaviors studied and compared to the ones incorporating γ(Ni) binders. The cermets ...with γ/γ’ binders exhibited ∼80 % reduction in mechanical wear at 25 °C, which stemmed from the decreased ceramic particle size and enhanced hardness. Moreover, such cermets showed decreased oxidational wear by ∼30 % at 600 °C. This superior resistance was attributed to the formation of tribolayers comprising a surface TiO2 layer and a subsurface Al2O3 layer, which accommodated plastic strains and alleviated binder oxidation. This observation was well interpreted by thermodynamic calculations and first-principles results. Hence, this work provides a new approach for developing wear-resistant cermets based on the design of metallic binders.
•Wear behavior of Ti(C, N)-based cermets with γ/γ’ duplex phase binders was studied.•Tribolayer containing a top TiO2 layer and an underneath Al2O3 layer was captured.•The thermodynamics and the effect of oxides stratification at 600 °C were discussed.
Tailoring of individual single–atom-thick layers in nanolaminated materials offers atomic-level control over material properties. Nonetheless, multielement alloying in individual atomic layers in ...nanolaminates is largely unexplored. Here, we report 15 inherently nanolaminated V₂(AₓSn1-x)C (A = Fe, Co, Ni, Mn, and combinations thereof, with x ∼ 1/3) MAX phases synthesized by an alloy-guided reaction. The simultaneous occupancy of the 4 magnetic elements and Sn in the individual single–atom-thick A layers constitutes high-entropy MAX phase in which multielemental alloying exclusively occurs in the 2-dimensional (2D) A layers. V₂(AₓSn1-x)C exhibit distinct ferromagnetic behavior that can be compositionally tailored from the multielement A-layer alloying. Density functional theory and phase diagram calculations are performed to understand the structure stability of these MAX phases. This 2D multielemental alloying approach provides a structural design route to discover nanolaminated materials and expand their chemical and physical properties. In fact, the magnetic behavior of these multielemental MAX phases shows strong dependency on the combination of various elements.
•The U-Si-M (M=Al, Ti, V, Zr, Nb and Mo) isothermal sections at 973 K are calculated.•The isothermal sections reveal the solubilities of elements M in U3Si2.•The solubilities are negative to the ...electronegativity, atomic size and number of mesophases.•The element Al has the largest solubility in U3Si2 among elements M, while element Zr and Ti have minute solubility.
U3Si2 has been regarded as a promising candidate for the accident tolerant fuel (ATF) in light water reactors (LWRs). To improve the performance of U3Si2, metal M (M=Al, Ti, V, Zr, Nb and Mo) as additions is of great interest. Here we studied the phase diagrams of the U-Si-M systems using the CALPHAD (CALculation of PHAse Diagram) approach aided by the first-principles calculations, to explore the M solubility in U3Si2. The results show that the M solubility is closely related to the electronegativity, the atomic size and the number of mesophases. To be specific, the solubility of M increases with the decreased differences in radius and electronegativity between Si and M, as well as the reduced number of intermediate phases in the binary U-M and Si-M systems. In addition, Al has the largest solubility in U3Si2 among all the elements studied, whereas Zr and Ti have minute solubilities. These findings may facilitate the exploration and development of novel ATF materials.
The development of high-entropy ceramic nanomaterials has significant scientific and technological potential, yet studies on these materials are rare. Here, we successfully synthesize ...(Hf0.25Ta0.25Nb0.25Ti0.25)C high-entropy metal carbide (HEC-1) nanowires—a class of high-entropy ceramic nanomaterials—via a facile bamboo-based carbothermal method with an Fe-Ni catalyst. The growth of HEC-1 nanowires occurs through a classical vapor-liquid-solid mechanism based on the solubility of metal, carbon, and HEC-1 in the Fe-Ni alloy. After high-temperature treatment, HEC-1 nanowires show good thermal stability without morphological evolution below 1,600°C, while they evolve into “pearl-necklace”’-like nanostructures or particles above 1,600°C due to the Rayleigh instability mechanism. After high-pressure treatments, HEC-1 nanowires are broken into nanorods above 1 GPa, in which brittle fracture without any dislocations, slip bands, or amorphous shear bands is directly observed at nano and atomic scales.
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•(Hf0.25Ta0.25Nb0.25Ti0.25)C nanowires are synthesized via carbothermal method•The growth of the nanowires is governed by a classical vapor-liquid-solid mechanism•The nanowires are shown to exhibit excellent high-temperature resistance•The brittle fracture is observed directly for the nanowires at high pressures
Ma et al. report (Hf0.25Ta0.25Nb0.25Ti0.25)C high-entropy metal carbide nanowires that show a morphological evolution above 1,600°C and simultaneously exhibit a brittle fracture without any dislocations, slip bands, or amorphous shear bands above 1 GPa. This work may provide theoretical guidance for broad applications of high-entropy carbide nanowires.
•The CALPHAD approach simplifies the Pourbaix diagram construction process.•Pourbaix diagrams for ternary and quaternary systems with two phases in aqueous solutions can be rapidly constructed.•The ...calculated Pourbaix diagrams were successfully used to predict the corrosion trend of different Ni-based alloys.•The effect of Si/Y addition and Ni5Y precipitation on the structural evolution of the passive film was studied.•The accuracy of the calculated Pourbaix diagrams is verified by key experiments.
Pourbaix diagrams are calculated to describe electrochemical processes for alloys in aqueous solution. With the multi-component differentiation of alloy systems, the construction of Pourbaix diagrams is facing challenges, especially for non-single-phase alloy systems. In this study, the simultaneous construction of phase diagrams and Pourbaix diagrams were implemented for predicting the evolution of the phases in the immune and passive regions. The CALPHAD (CALculation of PHAse Diagram) approach was used to quickly access the Gibbs free energies of various phases and the chemical potential of the elements in the phases from the thermodynamic database of the Ni-Si-Al-Y system. The corrosion behavior of two typical Ni-Al-Si and Ni-Al-Y systems was investigated. Si and Y were added to Ni-based alloys to produce the solid solutions L12Ni3(Al,Si) and L12Ni3Al + Ni5Y, respectively. Calculations showed that NiO and Al2O3 make up the passive area of the Ni3Al1 alloy. The introduction of SiO2 and Y(OH)3 in the passive region separately helped to minimize the alloys' susceptibility to corrosion. However, Si reduced the thermodynamical possibility of NiO formation in the passive film, and the addition of Y caused extreme galvanic corrosion. Experiments on Ni-based alloys validated the results through electrochemical corrosion. It was also discovered that the presence of Ni5Y produced galvanic corrosion and that Si reduced the oxide in the passive film, causing pitting corrosion. The corrosion prediction of the quaternary alloys indicates that the solid solution of Si in Ni5Y reduces the galvanic corrosion effect and the dissolution of passive film. The current work demonstrates that phase diagrams and Pourbaix diagrams may be efficiently and accurately predicted using a well-constructed thermodynamic database, which has major implications for future studies on the corrosion behavior of multi-component alloys.
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At present, sanitary landfill is mainly used for domestic waste treatment in Shannan City, Tibet. However, there are few studies on heavy metals in the soil around the landfill in Shannan city. ...Therefore, the surrounding soil of Luqionggang landfill in Shannan City, Tibet Autonomous Region, is taken as the research object. In the study, the geo-accumulation index method, Nemerow comprehensive pollution index method and potential ecological risk index method are mainly used to evaluate the pollution and risk of heavy metals in the soil around the landfill site. The main results are as follows: The average pH value of the soil around the landfill site is 9.37, belonging to the strong alkaline range. The average values of heavy metals Hg and Ni in soil exceeded the background content, and the average contents of other heavy metals Cu, Pb, Zn, Cr, As and Cd did not exceed the background content. The average content of these eight heavy metals did not exceed the screening value of the national soil environmental quality standard. In the horizontal direction, the average content of heavy metal elements Cu, Cr, Cd, Hg and Ni is relatively high in the west. The average content of heavy metals As, Zn and Pb in the north, east and south is slightly higher than that in the west. And the farther away from the landfill, the less the soil is affected by heavy metals. The evaluation results of geo-accumulation index show that heavy metal Hg is the most affected. The average value of the comprehensive pollution index is 2.969, which is between 2 and 3, belonging to the moderate pollution level. And the west side of the landfill (downstream area) is greatly affected. The evaluation results of potential ecological hazard pollution index show that the potential risk index of single pollutants of heavy metals Cu, Pb, Zn, Cr, Ni, As and Cd belongs to low ecological hazard level, and the potential risk index of single pollutants of heavy metal Hg belongs to relatively heavy ecological hazard level. On the whole, the total potential risk coefficient belongs to medium pollution hazard degree. According to the correlation analysis, there is no significant correlation between heavy metal elements As and Hg and the other six heavy metal elements. In addition, the pollution source of heavy metal As may be mainly soil forming factors and the pollution source of Hg may be mainly human factors.
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