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Extensive experimental and computational studies have demonstrated outstanding physical and chemical properties of the novel materials of compositionally complex carbides (CCCs), enabling their promising applications in advanced fission and fusion energy systems. This perspective provides a comprehensive overview of radiation damage behavior reported in the literature to understand the fundamental mechanisms related to the impact of multi-principal metal components on phase stability, irradiation-induced defect clusters, irradiation hardening, and thermal conductivity of compositionally complex carbides. Several future research directions are recommended to critically evaluate the feasibility of designing and developing new ceramic materials for extreme environments using the transformative "multi-principal component" concept. Compared to the existing materials for nuclear applications including stainless steels, nickel alloys, ZrC, SiC, and potentially high-entropy alloys, as well as certain other compositionally complex ceramic families. CCCs appear to be more resistant to amorphization, growth of irradiation defect clusters, and void swelling. [ABSTRACT FROM AUTHOR]

Five high entropy carbide ceramics, (Hf0.2,Nb0.2,Ta0.2,Ti0.2,Zr0.2)C, (Cr0.2,Hf0.2,Ta0.2,Ti0.2,Zr0.2)C, (Hf0.2,Mo0.2,Ta0.2,Ti0.2,Zr0.2)C, (Hf0.2,Ta0.2,Ti0.2,W0.2,Zr0.2)C, and (Hf0.2,Mo0.2,Ti0.2,W0.2,Zr0.2)C, were synthesized by carbothermal reduction of oxides and direct current sintering. The five high entropy carbide ceramics were determined to be nominally phase-pure with relative densities of more than 98.9% and mean grain sizes of less than 5 μm. Average Vickers hardness values ranged from 19.2 ± 0.4 GPa for (Hf0.2,Nb0.2,Ta0.2,Ti0.2,Zr0.2)C at a load of 2 kgf to 43.5 ± 0.4 GPa for (Hf0.2,Mo0.2,Ti0.2,W0.2,Zr0.2)C at a load of 0.05 kgf. Hardness generally increased with increasing the valence electron concentration and strain as measured by the Williamson–Hall analysis. However, neither correlation was conclusive enough to be a clear indicator of hardness. Instead, it was determined that a combination of effects that includes the valence electron concentration, lattice strain, and grain size all contribute to the hardness of high entropy carbide ceramics. [ABSTRACT FROM AUTHOR]

Since the form of the exact functional in density functional theory is unknown, we must rely on density functional approximations (DFAs). In the past, very promising results have been reported by combining semi-local DFAs with exact, i.e. Hartree–Fock, exchange. However, the spin-state energy ordering and the predictions of global minima structures are particularly sensitive to the choice of the hybrid functional and to the amount of exact exchange. This has been already qualitatively described for single conformations, reactions, and a limited number of conformations. Here, we have analyzed the mixing of exact exchange in exchange functionals for a set of several hundred isomers of the transition metal carbide, Mo4C2. The analysis of the calculated energies and charges using PBE0-type functional with varying amounts of exact exchange yields the following insights: (1) The sensitivity of spin-energy splitting is strongly correlated with the amount of exact exchange mixing. (2) Spin contamination is exacerbated when correlation is omitted from the exchange-correlation functional. (3) There is not one ideal value for the exact exchange mixing which can be used to parametrize or choose among the functionals. Calculated energies and electronic structures are influenced by exact exchange at a different magnitude within a given distribution; therefore, to extend the application range of hybrid functionals to the full periodic table the spin-energy splitting energies should be investigated. [ABSTRACT FROM AUTHOR]

Metal carbides are widely used in various applications as catalysts, components of composite materials, cutting tools, and abrasive materials where the particle/grain size has a great impact on target properties. Here, we report a facile way to synthesize nano- and ultra-fine carbides of IVb-Vb groups, including high-entropy carbides, which are of interest nowadays due to their superior properties, by the combination of calcium-hydride reduction of metal oxides and the direct reaction of the reduced metals with carbon in one production step. By tailoring the synthesis parameters, it is possible to obtain the carbide powders of a size in the range of 50–1500 nm with high crystallinity. The average particle size is found to be dependent on the homologous synthesis temperature and follows a power law. We have also shown the possibility of obtaining ultrafine-grained bulk carbides (d = 0.24–0.9 μm) via spark-plasma sintering at a temperature of 1500–1650 °C with a relative density >95 % without using additives. The HEC (Ti,Zr,Nb,Hf,Ta)C has a higher activation energy of grain growth (collective recrystallization) compared to binary TaC x (x = 0.8 and 1), which confirms the effect of lattice distortion on diffusion coefficients. The suggested fabrication route can be widely used for nano and ultrafine carbide powder preparation on the industrial scale. [ABSTRACT FROM AUTHOR]

A series of high-entropy carbide ceramics with high-performance were successfully prepared by SPS using self-synthesized fine high-entropy carbides powders as hard phase and metal Co as the binder. The effects of Ti and/or Mo addition on densification, grain size and mechanical properties of (ZrHfTaNb)C–10Co ceramic were investigated. The results showed that the addition of Mo improved the wettability between the ceramic phase and Co phase, and significantly increased the densification degree of the ceramics. In addition, the average grain size decreased and the microstructure became more uniform after adding Ti and/or Mo. Compared with the mechanical properties of (ZrHfTaNb)C–10Co ceramic, those of (ZrHfTaNbTiMo)C–10Co ceramic were greatly enhanced under the action of high-entropy effect and solid solution strengthening. The hardness and fracture toughness of the (ZrHfTaNbTiMo)C–10Co ceramic achieved the satisfactory values of 20.37 GPa and 8.59 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

Fabricating and introducing new materials with new features is one of the most important goals for many scientific groups. Today, additive manufacturing (AM) is known as one of the new production methods, which can create an excellent opportunity for achieving this goal. As one of the ongoing production processes, the laser AM (LAM) methods have the proper capacity for producing new advanced materials like carbide, nitride, and boride‐based materials. Hence, this work aims to review carbide‐based materials produced by LAM techniques with the composite viewpoint. These materials can act as a matrix, reinforcement, or tertiary component in advanced composites. With this viewpoint, these composite materials were introduced in eight separate sections, which are tungsten carbide, titanium carbide, silicon carbide, niobium carbide, chrome carbide, vanadium carbide, and boron carbide, as well as high entropy alloy composites. [ABSTRACT FROM AUTHOR]

The fatigue crack growth behavior of a submicron-grained WC–Co hardmetal is investigated by artificially introducing small flaws by means of sharp indentation. Similar fatigue testing is also conducted on notched specimens with long through-thickness cracks for comparison purposes. The use of controlled small indentations flaws is shown to be a valid and successful approach for studying and describing crack growth behavior under cyclic loading for the material under consideration. This statement is based on the similitude found in fatigue mechanics and mechanisms between both crack types. Regarding the former, accounting of the indentation-induced residual stresses is key to rationalize the experimental findings. Concerning the latter, inspection of crack-microstructure interaction as well as fracture surfaces permit to discern similar features and scenarios, at both meso- and micrometric length scales. Results from this research yield an immediate practical implication, as indentation techniques may then be proposed as an alternative testing route for investigating fatigue crack growth behavior of hardmetal grades where sharp indentation is capable to induce well-developed radial crack systems. [ABSTRACT FROM AUTHOR]

In this paper, we examine the cleavage fracture anisotropy in tantalum carbides, namely, TaC, α‐Ta2C, and ζ‐Ta4C3 − x, using density functional theory (DFT) calculations. Our investigation identifies the presence of multiple low‐energy cleavage planes indicating multiple potential pathways for crack propagation in these ceramics, even the low symmetry compounds. The anisotropy characteristics of cleavage fractures exhibited by α‐Ta2C and ζ‐Ta4C3 − x closely align with the intrinsic fracture anisotropy observed in TaC. Notably, there exist at least three pyramidal planes in ζ‐Ta4C3 − x whose cleavage energies are less than those of the carbon‐depleted basal planes, previously reported to have the lowest cleavage energy. The observed preference in experiments for cleavage along carbon‐depleted basal planes, exclusive of other identified low‐energy planes, points to factors beyond cleavage energy influencing cleavage plane preference. [ABSTRACT FROM AUTHOR]

While binder jetting (BJ) additive manufacturing (AM) holds considerable promise for industrial applications, defects often compromise part quality. This study addresses these challenges by investigating binding mechanisms and analyzing common defects, proposing tailored solutions to mitigate them. Emphasizing defect identification for effective quality control in BJ-AM, this research offers strategies for in-process rectification and post-process evaluation to elevate part quality. It shows how to successfully process metallic parts with complex geometries while maintaining consistent material properties. Furthermore, the paper explores the microstructure of AISI M2 tool steel, utilizing advanced image processing techniques like digital image analysis and SEM images to evaluate carbide distribution. The results show that M2 tool steel has a high proportion of M6C carbides, with furnace-cooled samples ranging from ~2.4% to 7.1% and MC carbides from ~0.4% to 9.4%. M6C carbides ranged from ~2.6% to 3.8% in air-cooled samples, while water-cooled samples peaked at ~8.52%. Sintering conditions also affected shrinkage, with furnace-cooled samples showing the lowest rates (1.7 ± 0.4% to 5 ± 0.4%) and water-cooled samples showing the highest (2 ± 0.4% to 14.1 ± 0.4%). The study recommends real-time defect detection systems with autonomous corrective capabilities to improve the quality and performance of BJ-AM components. [ABSTRACT FROM AUTHOR]

Thermal and electrical properties were investigated for five nominally phase‐pure high entropy carbide ceramics. The compositions (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C, (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Mo0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Ta0.2Ti0.2W0.2Zr0.2)C, and (Hf0.2Mo0.2Ti0.2W0.2Zr0.2)C were synthesized by carbothermal reduction of oxides. The thermal diffusivity and heat capacity were measured from room temperature to 1800°C. The room temperature thermal conductivity ranged from 5.1 W/mK for (Hf0.2Mo0.2Ti0.2W0.2Zr0.2)C to 9.0 W/mK for (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C. The thermal conductivity increased over the temperature range with maximum conductivities of 19.6 W/mK measured for (Hf0.2Mo0.2Ta0.2Ti0.2Zr0.2)C to 29.7 W/mK for (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C at 1800°C. The electron contribution to thermal conductivity calculated from measured electrical resistivity varied from 41% to 52% of the total thermal conductivity. The tungsten and molybdenum containing compositions had higher phonon contributions while the niobium and chromium containing compositions had nearly equal electron and phonon contributions to thermal conductivity. [ABSTRACT FROM AUTHOR]

The effect of addition of various metal carbides on the electrical, thermal, and mechanical properties of porous SiC ceramics was investigated. The results showed a decrease in the electrical resistivity from 1.2 × 102 to 1.3 × 10−3 Ω‧cm and thermal conductivity from 14.2 to 3.6 W.m−1K−1 whereas the compressive strength increased from 12.7 to 21.1–81.1 MPa at ∼60.2% porosity. The decrease in electrical resistivity and thermal conductivity was caused by the introduction of conductive carbides and multiple heterophase interfaces, respectively, in the porous ceramics. The electrical and thermal conductivities and compressive strength of porous SiC-based ceramics, processed with a SiC-B 4 C-VC-ZrC-NbC composition, were 8.0 × 102 Ω−1‧cm−1, 3.6 W‧m−1K−1, and 58.0 MPa, respectively. Therefore, it is proven that the electrical, thermal, and mechanical properties of porous SiC ceramics can be tuned over a wide range by adding a suitable combination of metal carbides. [ABSTRACT FROM AUTHOR]

The reaction between ZrC and iridium powders was studied in the temperature range of 1000–1600°C. The reaction was stated to start at a temperature as low as 1000°C. The only high‐melting intermetallic phase, ZrIr3, was obtained as a substitutional solid solution ZrIr3±δ. A new analytical approach to relating the composition to the lattice parameter of cubic binary substitutional ZrIr3±δ solid solutions was proposed. This approach is based on comparing the distribution by elemental composition and by lattice parameter in a range of ZrIr3±δ solid solutions. This made it possible to determine the lattice parameter of a stoichiometric ZrIr3 phase, a0 = 3.971(5) Å. [ABSTRACT FROM AUTHOR]

High entropy alloys containing equimolar multi-element composition enhance physical properties over traditional alloys. The concept was applied also for high entropy ceramics, but the solid-state reaction is necessary. In this work, high entropy alloy VNbMoTaW reacted with carbon to form high entropy carbide. Direct reaction in Spark Plasma Sintering (SPS) conditions leads to high entropy or entropy aided carbides depending on the amount of present carbon. The entropy aided carbide formed at low carbon concentrations below 0.8 of equimolar content contained all metallic elements, but two separated phases were identified: Nb, Ta or W, Mo rich. The microstructure of the entropy aided carbides is lamellar and refined compared to high entropy carbide (V 0.2 Nb 0.2 Mo 0.2 Ta 0.2 W 0.2)C 0.8. The presence of entropy aided carbide decreased the Vickers hardness from 23 GPa to 19 GPa, however, the unique microstructure might enhance other physical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Ultrafine tungsten carbide (WC)–cobalt (Co) and WC–(Ti,W)C–Co end mills were produced via spark plasma sintering. The wear mechanism of these end mills during machining of AISI H13 steel was investigated. WC–Co exhibits good mechanical properties (HV30: 2110 kg/mm2, KIC: 10.4 MPa/m1/2, TRS: 1990 MPa). Although the high hardness of WC–Co makes it show excellent resistance to abrasive wear, it suffers from a significant adhesion problem. As the cutting temperature increases, the oxidation of the WC–Co causes damage to the microstructure of tool materials, which deteriorates the grain boundary strength and promotes adhesive wear. This phenomenon causes large areas of tool materials to chip off and eventually results in cutting‐edge breakage. The high brittleness of (Ti,W)C causes cracks to propagate at low‐stress levels, reducing the mechanical properties of WC–(Ti,W)C–Co (KIC: 8.8 MPa/m1/2, TRS: 1090 MPa). However, (Ti,W)C addition enhances the resistance to oxidation and workpiece adhesion, which reduces the tool material loss caused by adhesive wear. The tool life of WC–(Ti,W)C–Co is three times longer than that of WC–Co in milling of AISI H13 at the same cutting speed. The key to maximizing the mechanical properties of ultrafine cemented carbide tools when machining AISI H13 is the modification of anti‐adhesive wear of surface. [ABSTRACT FROM AUTHOR]

This study binder jets a tungsten carbide‐nickel (WC‐Ni) sintered‐agglomerated composite powder, and postprocesses the preforms using an initial sintering step followed by a hot isostatic pressing (HIP) step. The effects of sintering temperatures, sintering durations, and HIP temperatures on notable properties (e.g., porosity, microstructure, hardness, and oxidation behavior) are quantified. The highest average relative density produced in this study was 96.8%, and volumetric shrinkage of these coupons was about 64%. Microstructural characterization shows that the WC grains are homogenously distributed throughout the nickel matrix and grow to an average diameter of 1.6 μm${\mathrm{\mu m}}$ (a 60% increase) during processing. X‐ray diffraction patterns indicate that no unwanted products were formed. Processed coupons achieved a maximum hardness of 54 Rockwell C, limited by their internal porosity. Oxidation tests result in the production of WO3 and NiWO4 at temperatures above 600°C. Methodologies and results from this study can be leveraged to additively manufacture highly dense, geometrically complex WC‐Ni parts with small carbide grains, low nickel content, desirable microstructure, and suitable functional properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • N- and F-doped bimetallic carbides (C 19 Cr 7 Mo 24) are synthesized at 1300 °C. • Both show excellent stability and higher ORR activities than Pt/C. • Electron transfer leads to excellent activity and stability. • F dopant more favors electron transfer than the N dopant. • Bimetallic carbide more favors electron transfer than monometallic carbide. Nitrogen- and fluorine-doped bimetallic carbide composites with graphite matrix (abbreviated as C 19 Cr 7 Mo 24 /NG and C 19 Cr 7 Mo 24 /FG) are synthesized through carbonization at 1300 °C. The C 19 Cr 7 Mo 24 /NG displays an initial half-wave potential (E 1/2) of 0.873 V and suffers merely 3 mV decrease in E 1/2 within 60,000 CV cycles for oxygen reduction reaction (ORR) in alkaline media. A H 2 /O 2 fuel cell testing system using the C 19 Cr 7 Mo 24 /NG as cathode maintains 95.9% of the initial peak power density (1.08 W cm−2) within 60,000 cycles. The C 19 Cr 7 Mo 24 /FG shows higher ORR activity than the C 19 Cr 7 Mo 24 /NG. The positive and negative charge centers caused by the N or F dopants are the critical reasons to their high activities. While F and bimetallic carbide more favor electron transfer respectively than the N and monometallic carbide. Their excellent stabilities originate from interactions among atoms due to electron transfer and the intrinsic chemical inertness of graphite and bimetallic carbides. [ABSTRACT FROM AUTHOR]

(CoCrNiMoW)-WC composites were prepared by powder metallurgy. The microstructure, tribological properties and wear mechanisms of the composites were investigated at room temperature, 400 °C, and 800 °C. Multiple carbides are generated in situ in the sintered composites. Increased WC content enhanced the hardness and promoted the microstructural evolution of the composites. The phase composition of the composite changes from FCC phase + η carbide to FCC phase + η carbide + WC + Cr 23 C 6 , and the microstructure changes from individual island-like to connected island-like structure. High-temperature negative wear phenomena were observed in the 30 wt % and 50 wt % WC-added composites at 800 °C, which contributed to the friction-induced high-temperature oxide volume increase compensating for the volume loss due to wear. [ABSTRACT FROM AUTHOR]

Three multi-phase tantalum carbide composites (TaC z -Ta 5 Si 3) were fabricated by Spark plasma Sintering (SPS) using Ta, TaC and SiC powders. SiC was added to control the C:Ta ratio (z = 0.6, 0.74, 1.0), regulating the phase composition and grain morphology while also serving as a deoxidizer. Composite TaC 0.6 -Ta 5 Si 3 had Ta 2 C as the major phase and contained Ta 4 C 3−x , TaC and Ta 5 Si 3. It exhibited an excellent combination of high flexure strength (714 ± 21 MPa) and toughness (13.9 ± 0.2 MPa·m1/2), despite a low Ta 4 C 3−x fraction, a phase known to have very high toughness. The outstanding performance was attributed to the elongated Ta 2 C grain morphology, highly laminated intra-granular Ta 4 C 3−x laths, and the refined Ta 2 C grain size. Composite TaC 0.74 -Ta 5 Si 3 , characterised by equiaxed grain morphology, exhibited good flexure strength (571 ± 36 Mpa) and toughness (7.6 ± 1.1 MPa·m1/2) due to the presence of Ta 4 C 3−x laths in the c-TaC. Lastly, composite TaC 1.0 -Ta 5 Si 3 , composed of c-TaC and Ta 5 Si 3 , exhibited moderate strength (545 ± 25 MPa) and toughness (5.3 ± 0.1 MPa·m1/2). • Ta 2 C-dominant and TaC-dominant composites (TaC z -Ta 5 Si 3) are fabricated using Ta, TaC and SiC. • SiC additives control the C:Ta and effectively promoted the sintering through oxide removal. • TaC 0.6 -Ta 5 Si 3 has the best toughness due to the elongated Ta 2 C grains and intra-granular laths. • TaC 0.74 -Ta 5 Si 3 with the equiaxed TaC has good toughness due to the intra-granular laths. • TaC 1.0 -Ta 5 Si 3 with the equiaxed TaC is free of intra-granular laths and has the lowest toughness. [ABSTRACT FROM AUTHOR]

(TiZrNbTaCr)C high-entropy carbide ceramics with different Cr content are fabricated by hot-pressing and the mechanical properties are tested. With increasing Cr content, the fracture mode changed from intergranular to transgranular. Nanoindentation tests indicated that this transition is ascribed to the enhancement of grain boundary strength and atom probe tomography (APT) analysis confirmed indeed different grain boundary impurity concentration ascribed to a purification effect of Cr carbide. Besides, the mismatch degree between the atoms at and in the vicinity of grain boundaries as well as the grain size may also impact grain boundary strength. The fracture toughness presents a decline tendency with increasing Cr content, and its relationship with fracture mode transition is discussed. [ABSTRACT FROM AUTHOR]

The carbide gradation related to geometry size and local stress concentration sensitivity significantly impacts the performance of the carburized 16Cr3NiWMoVNbE steel. The conventional metallurgical graphic comparison method by manual comparison is not capable of grading the carbide gradation automatically. A novel method is thus introduced to automatically evaluate the carbide grade by using a new shape factor φsc with stress distribution analysis instead of using the circularity or roundness shape factor which only considers the geometry shape of carbide particles. The logarithm of the stress concentration factor ln(K) is linearly related to the logarithm of the shape factor ln(φsc). The gradient b of the fitted straight line shows sensitivity to the carbide grade. The gradients are b1 = 0.039, b3 = 0.049, and b5 = 0.055 for the three carbide classes from low to high. Furthermore, there is also a linear relationship between hardness in different grades of carbide microstructure and the gradient b. [ABSTRACT FROM AUTHOR]

The effects of Ce on inclusions and the primary carbide network of AISI 440C bearing steel are experimentally and theoretically investigated. Adding Ce improves the cleanliness and refinement of primary carbide networks in AISI 440C bearing steel ingots. The addition of Ce substantially reduces the contents of total oxygen (T.O) and S in the steel, and MnS and Al2O3 inclusions are modified into finer Ce‐containing inclusions (Ce2O2S and Ce2O3). When Ce is added, the average equivalent diameter of the inclusions decreases from 1.82 to 1.33 μm, and the number of inclusions per unit area (mm2) increases from 59 to 105. Moreover, the addition of Ce reduces the secondary dendrite spacing from 33.82 to 24.2 μm, and the proportion of primary carbide is reduced from 22.08% to 11.17%. The 2D lattice disregistry theory confirms that Ce2O2S and Ce2O3 inclusions can be utilized as effective heterogeneous nucleation cores for γ‐Fe, thus refining the solidification microstructure and also the primary carbide. This study provides theoretical guidelines for the fabrication of domestic AISI 440C bearing steel ingots. [ABSTRACT FROM AUTHOR]

The types, distribution, morphology, orientation, growth, and aggregation mechanism of primary carbides in the continuous casting slab of 6Cr13 high‐carbon martensitic stainless steel are investigated. In the results, it is shown that M7C3 carbides precipitate from the liquid steel at the end of solidification. The area fraction of primary carbides in the slab thickness direction shows an overall decreasing trend from the center to the edge. And, the closer to the center region, the greater the difference in carbide distribution due to the presence of spot segregation defects. At 1/8 thickness and edges in the slab, the fast cooling rate and fine dendrites make the carbide morphology to be a small‐sized brain like that aggregates a large number of spherical carbides. At 1/4 thickness in the slab, blocky, fibrous, and spherical carbides precipitate successively and eventually aggregate together. At 3/8 thickness and center in the slab, the cooling rate is slower and spot segregation defects are randomly distributed in this region. The carbide morphology is mostly small‐sized brain like in the non‐spot segregation region. However, the alloying elements are highly supersaturated and the carbides can grow sufficiently to form less oriented, large‐sized brain‐like carbide in the spot segregation region. [ABSTRACT FROM AUTHOR]

A novel technique to simultaneously lower the synthesis temperature of highentropy carbides and maintain their high mechanical properties was proposed. Certain amount of carbon vacancies was first introduced to significantly lower the temperature down to 2000°C for uniform elemental distributions in highentropy carbides. Those carbon vacancies were then fully eliminated through the reaction between high-entropy carbides and certain amount of boron carbide. Concomitantly, the high-entropy boride phasewas formed. The elimination of carbon vacancies and the formation of high-entropy boride phase significantly improved the mechanical properties of the high-entropy carbides. A high mechanical strength over 500 MPa can be obtained by phase optimization. [ABSTRACT FROM AUTHOR]

To satisfy the needs of precision machining, ultrafine tungsten carbide (WC)-based cemented carbide with fine grain size and excellent mechanical properties was prepared. Ultrafine cemented carbide was prepared by spark plasma sintering (SPS) using WC, Co as raw materials and metal elements V, and Cr as additives, and the effects of metal elements on the microstructure and mechanical properties of cemented carbide were investigated. The results show that the specimen (91.6WC-1.2V-1.2Cr-6Co) prepared at 1350 °C, 6 min, 25 MPa has the best mechanical properties (HV 2322.9, KIC 8.7 MPa·m1/2) and homogeneous microstructure. The metal elements could react with WC to form a (W, V, Cr) Cx segregation layer, which effectively inhibits the growth of WC grains (300 nm). The combination of SPS and metal element additives provides a new approach for the preparation of ultrafine cemented carbides with excellent properties. [ABSTRACT FROM AUTHOR]

Common high-temperature thermoelectric materials' expensive and rare element contents create a need to develop readily available and cost-effective materials such as carbides, as they have naturally abundant constituents, low costs, and good high-temperature performance. Although there are published research results on the thermoelectric properties of B4C and SiC, they vary widely in production and characterization methods, hence the results. To efficiently compare these materials and initiate a starting point for material selection for developing thermoelectric ceramics and composites as alternatives to toxic and costly common high-temperature thermoelectric materials, B4C, SiC, and TiC were spark plasma sintered under similar conditions with different sintering temperatures due to the different characteristics of the materials. Their thermoelectric properties were analyzed between 323 and 923 K and compared. Thermoelectric properties of TiC were investigated in detail for the first time. The results demonstrated that SiC has a high Seebeck coefficient (564.4 µV/K), low electrical (602.1 S/m), and high thermal conductivity (65.8 W/mK), B4C has high electrical (6974.8 S/m) and low thermal conductivity (12.4 W/mK), and relatively high Seebeck coefficient (269.5 µV/K). In contrast, TiC has metallic electrical (1.3 × 106 S/m) and relatively low thermal conductivities (32.8 W/mK) while a very low Seebeck coefficient (-9.9 µV/K). [ABSTRACT FROM AUTHOR]

Instrumented indentation experiments at elevated temperatures require careful attention to a myriad of experimental details. Not the least of these is the choice of the indenter tip material. Traditional room-temperature indenters, e.g., diamond and sapphire, can break down, react, and wear excessively at elevated temperatures. In this work, rf-induction heating float-zone and high-temperature solution single-crystal growth techniques have been used to prepare a suite of bulk refractory carbide specimens (i.e., ZrC, VC0.86, NbC, TiC0.95, WC). These potential indenter tip materials were subsequently characterized using nanoindentation testing techniques to determine their single-crystal elastic modulus, hardness, and fracture toughness in order to evaluate their potential for use as elevated-temperature nanoindentation tips. Additionally, subject carbide crystal characteristics were compared to those of single-crystal sapphire and polycrystalline WC-Co. The cumulative results show that single-crystal WC is a promising candidate for indenter tip material based on a combination of its high elastic modulus, hardness, and resistance to cracking—in addition to being crystallographically favorable for fabrication in the frequently used three-sided pyramidal indenter tip geometries. [ABSTRACT FROM AUTHOR]

Ultra-high temperature ceramics (UHTCs) are refractory transition-metal carbides, nitrides, and borides with the highest melting temperatures known materials, making them prime candidates for applications in aerospace and hypersonic vehicles. Of the UHTCs, tantalum carbide (TaC) and hafnium carbide (HfC) feature the highest melting temperatures. We investigated the binderless consolidation of HfC/TaC powder blends using Field Assisted Sintering Technology (FAST). Powders consisting of 90/10, 50/50, and 10/90 vol% HfC:TaC were sintered to high densities (>94 %). Bulk and nanomechanical, chemical, and microstructural characterization revealed substantially greater strength, hardness, and stiffness for ternary alloys. Mechanical properties correlated with physiochemical analysis indicated trace oxygen phases, solid-solution strengthening, and nonstoichiometric carbon were the key mechanisms driving the peak property enhancement of the 50 vol% solid-solution sample, despite lower densities. This study provides insight into optimizing the compositional design of HfC-TaC alloys by balancing influences from solid solution strengthening and the thermodynamic effects of oxygen/carbon stoichiometry. [ABSTRACT FROM AUTHOR]

High-entropy carbides with tunable crystallization and growth have been demonstrated using single-source precursor derived ceramic route. The in situ nanocrystallization of high-entropy carbide phases, (Ta 0.2 W 0.2 V 0.2 Mo 0.2 Nb 0.2)Si δ C and (Ta 0.167 W 0.167 V 0.167 Mo 0.167 Nb 0.167 Si 0.167)C in amorphous Si-based ceramic matrices was achieved by using polysiloxanes and polycarbosilanes as polymer precursors respectively. The results exemplify a prominent role of the architectures of the polymeric precursors in controlling the structural features of these ceramics at various length scales. In particular, it was observed that high-entropy carbides with rock salt and zinc blende crystal structures were formed when polysiloxanes and polycarbosilanes with different backbone structure were used as polymeric precursors respectively. This is attributed to the thermodynamics of nucleation of the carbidic phases in these nanocomposites. Furthermore, the precursor architecture that dictates free carbon content, influenced nanostructural features and porosity in the material. Therefore, engineering such compositionally complex phases is feasible by selecting suitable polymeric precursors. • Precursor architecture influenced the crystal structure of high-entropy carbides. • Crystal structure dependent on earliest nucleated carbidic phase. • Free carbon played a key role in controlling crystallite size and porosity. [ABSTRACT FROM AUTHOR]

The ablation behavior of (Hf 0.25 Zr 0.25 Ti 0.25 Ta 0.25)C was investigated using a plasma flame gun over a wide temperature range of 2070–2600℃. The structural transformation during ablation and the effect of temperature on the failure mechanism were discussed. Results showed a sharp increase in mass and linear ablation rates from 0.23 mg·cm−2·s−1 and 4.6 μm·s−1 at 2070℃ to 4.6 mg·cm−2·s−1 and 37 μm·s−1 at 2600℃. This variation was attributed to the temperature's impact on on the microstructure and composition of the oxide layer. During ablation, Hf/Zr-rich oxycarbides preferentially nucleated within the amorphous Hf-Zr-Ti-Ta-C-O layer, leading to phase separation of the oxide layer. With increasing ablation temperature, the filler and binder oxides with low melting point (e.g., (Hf,Zr)TiO 4 , TaZr 2.75 O 8) were rapidly consumed. The skeleton oxides (e.g., (Hf,Zr)O 2) failed to bond and peeled off. The transiently formed (Hf,Zr,Ti,Ta)O x layer was repeatedly destroyed and reconstructed, resulting in the continuous damage and eventual failure of the matrix. • Carbides experience a structural transition from amorphous to crystalline oxycarbides during the initial stage of ablation. • Phase separation occurs in the oxide and the oxycarbide layer. • The failure behavior of high-entropy carbides is primarily determined by the consumption of low-melting-point oxides. [ABSTRACT FROM AUTHOR]

Novel charge distribution regulation strategy for Mo 2 C, the relationships of Interface-Structure-Property in heterostructures were clarified, facilitating efficient adsorption-catalysis of Li 2 S x (1≤x≤4) [Display omitted] • A novel electronic distribution regulation strategy (Mo-Mo 2 C heterostructure) for molybdenum carbide was developed. • The relationship of the heterointerfaces-structure–property in Mo-Mo 2 C has been clarified. • The modulation of the intrinsic electronic distribution of Mo 2 C results higher adsorption energy for lithium polysulfides (LiPSs) and stronger Mo-S bonding strength. • The sulfur cathode with C@Mo-Mo 2 C an excellent high-rate cyclic performance accompanied by capacity decay rate of 0.08 % per cycle after 400 cycles at 2 C. Heterostructure engineering is considered a crucial strategy to modulate the intrinsic charge transfer behavior of materials, enhance catalytic activity, and optimize sulfur electrochemical processes. However, parsing the role of heterogeneous interface-structure–property relationships in heterostructures is still a key scientific issue to realize the efficient catalytic conversion of polysulfides. Based on this, molybdenum carbide (Mo 2 C) was successfully partial reduced to molybdenum metal (Mo) via a thermal reduction at high-temperature and the typical Mo-Mo 2 C-based Mott-Schottky heterostructures were simultaneously constructed, which realized the modulation of the electronic structure of Mo 2 C and optimized the conversion process of lithium polysulfides (LPS). Compared with single molybdenum carbide, the modulated molybdenum carbide acts as an electron donor with stronger Mo-S bonding strength as well as higher polysulfide adsorption energy, faster Li 2 S conversion kinetics, and greatly facilitates the adsorption → catalysis process of LPS. As a result, yolk-shell Mo-Mo 2 C heterostructure (C@Mo-Mo 2 C) exhibits excellent cycling performance as a sulfur host, with a discharge specific capacity of 488.41 mAh g−1 for C@Mo-Mo 2 C/S at 4 C and present an excellent high-rate cyclic performance accompanied by capacity decay rate of 0.08 % per cycle after 400 cycles at 2 C. Heterostructure-acting Mo 2 C electron distribution modulation engineering may contributes to the understanding of the structure-interface-property interaction law in heterostructures and further enables the efficient modulation of the chemical behavior of sulfur. [ABSTRACT FROM AUTHOR]

This work studied and compared the evolutions of irradiation-induced microstructural defects in five high-entropy carbide ceramics (HECCs) at room temperature to reveal the irradiation resistances of HECCs and corresponding underlying mechanisms. The five HECCs exhibit high phase stabilities and no amorphization is observed up to 40 dpa. In-situ 800 keV Kr ion irradiation reveals similar evolutions of irradiation-induced defects. The densities of dislocation loops show non-monotonic variations, which reach the maximum at ∼ 2 dpa and then decrease due to the interactions with each other. In contrast, the sizes of dislocation loops increase monotonically with dose. (NbTaZrW)C exhibits the lowest defect densities and highest defect sizes, which is probably due to the high lattice distortion and its induced high defect recombination efficiencies. Based on the characterization results, it is deduced that the species of constituent elements play more important role in the defect behaviors than the number of constituent elements. [ABSTRACT FROM AUTHOR]

In industrial practice, combining grain growth inhibitors (GGIs) with low carbon content effectively restrains WC grain growth in WC-Co cemented carbides. However, the intricate relationship between carbon content, WC grain microstructure, and GGI impact remains unresolved. This study investigates two WC-Co sample sets, maintaining constant VC inhibitor levels but varying carbon content near upper (HC) and lower (LC) limits. SEM analysis revealed distinct morphologies: HC displayed truncated prism shapes, exposing long basal and prismatic terraces, while LC exhibited a saw-tooth morphology with finer grains. EBSD stereology quantified anisotropic WC grain growth, revealing suppressed growth perpendicular to both basal (HC: 0.51 μm vs. LC: 0.38 μm) and prismatic planes (HC: 0.44 μm vs. LC: 0.37 μm) with decreased carbon content. Atomic-resolution EDS showed higher V solute excess in LC at WC(basal)-Co, WC(prismatic)-Co interfaces, and step corners (HC: 4.6, 0.9, and 4.4 atoms/nm2; LC: 5.5, 0.9, and 7.8 atoms/nm2). Our findings elucidate a clear physical understanding that a low carbon content enhances V atom solubility within liquid cobalt, increasing the thickness of complexions to quad-layer on WC (basal)-Co interfaces and forming V-rich nanoprecipitates at step corners. Those inhibitory effects further limited step flow, resulting in pronounced step bunching and a saw-tooth fine-grained morphology in LC sample. This study highlights that complexions housing more inhibitory solute elements exert a stronger drag effect on grain growth front migration. This approach has the potential for studying grain growth in anisotropic materials, highlighting the importance of constructing experimental complexion diagrams in engineering fine-structured ceramics and metals. [ABSTRACT FROM AUTHOR]

Tribological characteristics of fine-grained dual-phase high-entropy carbide/boride ceramics were investigated using the ball-on-flat dry sliding method in air, applying linear reciprocation motion with SiC counterpart. Detailed fractographical analyses were used for the characterization of the deformation and damage mechanisms. The investigated system with composition (Ti 0.14 Zr 0.2 Nb 0.2 Hf 0.2 Ta 0.26)C + (Ti 0.38 Zr 0.18 Nb 0.22 Hf 0.115 Ta 0.105)B 2 showed density with value 8.72 g/cm3 and very high hardness of HV1 29.4 ± 2.0 GPa. The friction coefficient at the test with 5 N was 0.56 and during the test with 10 N and 25 N loads were 0.48 and 0.5, respectively. The effective wear rates at the loads of 5 N and 25 N were very similar with values of 7.93 × 10−7 mm3/Nm and 6.63 × 10−7 mm3/Nm. At load 50 N the effective wear rate is significantly higher with a value of 9.11 × 10−6 mm3/Nm. Detailed fractography revealed that the dominant wear mechanisms at loads of 5 N and 25 N were an oxidation-driven tribochemical reaction and tribo-layer formation in boride grains and mechanical wear in carbide grains and at the load of 50 N fracture of boride and carbide grains and formation of chemically complex tribolayers. [ABSTRACT FROM AUTHOR]

The adoption of a continuous gradient in Co content stands as the foremost strategy for attaining heightened surface hardness and improved core toughness in cemented carbides. Nevertheless, the reduction in surface toughness stemming from a decreased Co content often precipitates premature surface failure of components. In this paper, WC-11Co powders was utilized as the precursor materials for fabricating a bidirectional gradient cemented carbide using the combined approach of low-temperature presintering and ultrasonic treatment techniques. The resultant cemented carbide exhibited a distinct gradient distribution, characterized by a forward gradient of graphene content, a reverse gradient of Co content, a forward gradient of WC grain size, and a forward gradient of residual compressive stress. The hardening and toughening mechanisms of the fabricated bidirectional gradient cemented carbides were comprehensively characterized and quantitatively discussed. The results provide compelling evidence that the gradient distribution of Co content plays a crucial role in attaining an impressive surface hardness of 1820 kgf/mm2. By utilizing the crack bridging mechanism of graphene, which efficiently exploits its strain transfer capabilities across a semi-coherent interface, in conjunction with the toughening effects of crack deflection and residual compressive stress, an exceptional surface fracture toughness of 17.62 MPa m1/2 is achieved. Additionally, the gradient layer exhibited a higher critical load for cracking. The present findings presents a novel strategy for the fabrication of high-performance ceramic-based composites. [ABSTRACT FROM AUTHOR]

To achieve Si‐free refractory ceramic matrix composites exposed to an oxidizing atmosphere at approximately 2000°C, a Ti–Zr–Mo ternary alloy melt‐infiltration (MI) method was developed for the production of carbon fiber‐reinforced refractory high‐entropy ceramic matrix composites (C/RHECs), with high‐entropy carbides serving as the matrix. This approach was designed using calculation phase diagrams (CALPHADs) and the calculation of thermodynamic parameters. The combination of CALPHAD and the calculation of alloy and carbon reactivity enabled the prediction of reaction and infiltration behavior into a preform comprising carbon fiber, carbon black, and transition metal carbide powders. Furthermore, C/RHECs featuring a (Ti, Zr, Hf, Nb, Ta, Nb, Mo)C matrix were experimentally fabricated through the Ti–Zr–Mo alloy MI method in accordance with the design. The arc‐wind tunnel tests on the C/RHECs conducted at approximately 2000°C revealed surfaces covered with complex oxides. The apparent oxidation rate of the C/RHECs was similar to that of Si‐containing ceramics and composites. These results indicate that complex oxides act as a barrier to oxygen diffusion toward unoxidized regions, making Si no longer essential for protecting materials from oxidation above 2000°C. [ABSTRACT FROM AUTHOR]

Powder synthesis is crucial for achieving the densification and facilitating widespread applications of high entropy carbide (HEC). Specifically, the production of fine particle‐size powders is essential to enhance the densification of HECs. Consequently, this paper proposes the molten salt method for synthesizing HEC powders. The synthesis process successfully yielded (Ta Nb Ti V) C powders with a particle size of only 0.44 µm at 1400°C, exhibiting a uniform distribution of each element. Subsequent densification of (Ta Nb Ti V) C within the 1700–1900°C temperature range was carried out using spark plasma sintering. It was observed that as the densification temperature increased, the densification and mechanical properties of HEC significantly improved. This study presents innovative ideas for the preparation of HEC at lower temperatures. [ABSTRACT FROM AUTHOR]

The (TiZrHfNbTaMo)C‐15 wt.% Co ceramics with excellent comprehensive properties were successfully prepared by vacuum liquid phase sintering. The effects of WC content on the grain size, microstructure, and mechanical properties were investigated. The results showed that WC was dissolved into (TiZrHfNbTaMo)C phase to form a seven‐component solid solution, and the independent WC phase disappeared. The addition of WC improved the wettability between the ceramic phase and the metal phase and promoted the densification of the ceramics. In addition, WC played a role in refining grains and inhibiting the grains growth to a certain extent. The comprehensive properties of ceramics were improved by solid solution strengthening and high entropy effect. When the WC content was 5 wt.%, the toughness reached the maximum of 9.41 ± 0.15 MPa·m1/2, and the hardness of the ceramic with 10 wt.% WC achieved the highest value of 18.18 ± 0.20 GPa. [ABSTRACT FROM AUTHOR]

In this study, based on different element configurations within constant atomic ratio of elements, (Ti 0.93 W 0.07 Mo 0.07)C–20%Ni and (Ti 0.93 W 0.07 Mo 0.07)CN 0.3 -20%Ni derived cermets have been synthesized. The basis for the difference in the production route was whether the carbides were formed by carbothermic reaction from the metal oxide together or separately, or in the case of Mo 2 C, the carbide is added to the mixture together with the binder after reduction and just before consolidation. Another basis for the difference was whether the cermet was a carbide or a carbonitride. To investigate the influence of the different production routes, the crystal structure, microstructure, and mechanical properties of the cermets produced were examined using XRD, FESEM, STEM, and Vickers indentation. The XRD spectra of all the cermets were found to be very similar to those of TiC-based cermets, indicating that the additive carbides in the TiC or Ti(CN) phases of the cermets dissolve perfectly during the high vacuum sintering process at 1510 °C. The highest toughness (14.65 MPa m1/2) was obtained in (Ti 0.93 W 0.07) C–8%Mo 2 C–20Ni cermets with a core-rim structure. In addition, the use of nitrogen leads to a dramatic reduction in particle size. The use of molybdenum and tungsten in the form of separate carbides had little effect on limiting the expansion of crystal size and grain size compared to the scenario where the dissolution of these elements took place within the primary core-rim structure. However, in terms of hardness and toughness, it was found that, in addition to grain size, the route taken in the addition of molybdenum and tungsten was also important. [ABSTRACT FROM AUTHOR]

To quickly screen for single-phased multi-principal-element materials, a so-called entropy forming ability (EFA) parameter is sometimes used as a descriptor. The larger the EFA, the larger is the propensity to form a single-phase structure. We have investigated this EFA descriptor with atomic relaxations in special-quasi-random structures and discovered that the EFA correlates inversely with the lattice distortion. Large effective atomic size differences lead to multi-phase compounds, and little size differences to single-phase compounds. Instead of configurational entropy, we therefore demonstrate the applicability of the Hume-Rothery rules to phase stability of solid solutions even in compositionally complex ceramics. [ABSTRACT FROM AUTHOR]

High-entropy carbides have attracted considerable attention owing to their high melting point and excellent mechanical properties at high temperatures. However, exposures to high temperature environments are often accompanied by oxidation problems. Previous studies generally focused on improving oxidation properties by adding antioxidant elements. However, improving the oxidation properties intrinsically by modifying the crystal structure is still lacking. In this work, we innovative introduced tunable carbon vacancies into high-entropy carbides successfully.Consequently, the oxidation property of high-entropy carbides was improved, with the effect of carbon vacancies on the oxidation property was systematically investigated in this study. The (Ti 0.2 V 0.2 Nb 0.2 Mo 0.2 W 0.2)C x exhibits the best oxidation resistance property when x = 0.7, with the highest initial oxidation temperature and peak weight gain temperature (950.2 °C) and the lowest mass gain rate (25.2 %). This is mainly attributed to the formation of a higher number of carbonaceous oxides, which hinder the internal oxidation process. [ABSTRACT FROM AUTHOR]

In order to clarify more clearly the action mechanism of Ti at the interface between Cu–Ti alloy and SiC during wetting, the monocrystal, polycrystalline, and porous α-SiC substrates were selected for study by modified sessile drop method under high vacuum at 1373 K. The results show that there is no significant difference in wettability and spreading dynamics between monocrystal and polycrystalline α-SiC substrates. The critical titanium concentration causing wettability transformation is between 5 wt% and 7.5 wt%. The transformation of wettability mainly depends on the precipitation of continuous Ti 3 SiC 2 layer with metalloid properties. Multilayer precipitation layers were observed in the interface structure, corresponding to three spreading stages: rapid spreading stage, which may be caused by TiC precipitation; At the stage of spreading stagnation, the corresponding interface failed to produce enough TiC; Slowly spreading to the equilibrium stage corresponds to the precipitation of Ti 3 SiC 2. Cu- x Ti on porous-SiC substrate failed to achieve complete pressureless infiltration during wetting, mainly because the volume of SiC and TiC consumed by the reaction is much smaller than the volume of the precipitated phase Ti 3 SiC 2 , which closed the pores and hindered the infiltration process. The results can provide theoretical basis for regulating the wettability, optimizing the interface structure between titanium-containing active alloys and carbide ceramics. [ABSTRACT FROM AUTHOR]

Zirconium carbide (ZrC) disks were fabricated using binder jet printing to study the effect of powder feedstock, print parameters, and heat treatment on flowability and final materials properties. A median volumetric particle size smaller than 10 μm was shown to cause the powder to stop flowing during printing. Disks were printed using ZrC with suitable flowability and then heat-treated at temperatures between 1800 °C and 2200 °C for 1 or 5 h. The density, part shrinkage, thermal diffusivity, and fracture strength all increased with increasing temperature and time. The heat-treated disks were then heated to 2200 °C for 5 h and the properties converged for disks of the same particle size, indicating the hottest temperature and longest time of exposure dictates the final properties. Lastly, it was shown that larger particles produce lower density materials with worse thermal diffusivity, most likely because of poor connectivity between particles after heat treatment. [ABSTRACT FROM AUTHOR]

(ZrHf x VNbMoW)C ceramics with different Hf contents are consolidated by hot-pressing sintering at 2100 °C for 1 h. The influence of Hf content and temperature on phase transition are investigated. The phase transition from single high-entropy phase to multi-phase containing (ZrHfNb)C-rich and (VMoW)C-rich intermediate phases occurs with adding Hf, in relation with relevant larger lattice distortion. Remarkable microstructure refinement is observed with Hf content variation, due to the poor sinterability of Hf and the intermediate phases restricting the atomic motion and diffusion. The refined microstructure and severe lattice distortion lead to the improvement in mechanical properties. The annealing at different temperatures further proves the phase stability, sluggish diffusion effect as well as solid solution diffusion in high-entropy and multi-phase carbides. • The addition of Hf leads to the phase transition from single high-entropy phase to multi-phase. • Due to the poor sinterability of Hf and the restriction of intermediate phases, the microstructure is much refined. • The annealing further proves the phase stability, sluggish diffusion effect as well as solid solution diffusion. [ABSTRACT FROM AUTHOR]

This work reviews the recent development of High Entropy Ceramics (HEC), which have five or more elements combined in equimolar or near equimolar quantities and have demonstrated unique properties. The comprehensive review is based on the general classifications of high entropy ceramics into carbides, borides, oxides, and other ceramic compounds. For each class of HECs, the synthesis processes, microstructure, and mechanical, thermal, and electrical properties are summarized in detail, with property data tables. Additionally, the fabrication and properties of HEC in the form of film, coatings, and composites are discussed. In addition to these material properties, this review article also highlights the utilization of computational studies and machine learning (ML) in the discovery of high entropy carbides. Finally, the overall conclusion of the current status and future research direction are discussed. [ABSTRACT FROM AUTHOR]