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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]

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]

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]

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]

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]

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]

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]

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]

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 Ni-based superalloy René 41 has sparked recent interest for applications in next-generation aircraft engines due to its high-temperature strength that is superior to all similar grades. These desirable properties are achieved by careful control of the microstructure evolution during thermomechanical processing, and this is commonly informed by simulations. In particular, the grain boundary carbides M6C and M23C6 play an essential role in controlling the grain size and strength of the final product. Therefore, a solid understanding of the thermodynamic stability and thermokinetic evolution of these carbides is essential. However, thermokinetic simulations using existing thermodynamic databases have been demonstrated to have discrepancies between thermodynamic stabilities and experimental observations. Here, we collected a new experimental time–temperature–precipitation diagram. In conjunction with improved crystallographic descriptions, these experimental results are used to modify a CALPHAD database for M6C and M23C6. The modified database correctly identifies temperature regions with rapid carbide precipitation kinetics. Further, kinetic simulations and strengthening models successfully predict the hardness increase due to γ′ precipitation. The modified database has been applied to Udimet 700, Waspaloy, and Haynes 282, demonstrating improved results. These updates will facilitate more accurate simulations of the microstructure evolution during thermomechanical processing of advanced Ni-based superalloys for aerospace and other applications. [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]

[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]

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]

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]

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]

Hf-based carbides are highly desirable candidate materials for oxidizing environments above 2000 °C. However, the static oxidation behavior at their potential service temperatures remains unclear. To fill this gap, the static oxidation behavior of (Hf, Ti)C and the effect of Ti substitutions were investigated in air at 2500 °C under an oxygen partial pressure of 4.2 kPa. After oxidation for 2000 s, the thickness of the oxide layer on the surface of (Hf, Ti)C bulk ceramic is reduced by 62.29 % compared with that on the HfC monocarbide surface. The dramatic improvement in oxidation resistance is attributed to the unique oxide layer structure consisting of various crystalline oxycarbides, HfO2, and carbon. The Ti-rich oxycarbide ((Ti, Hf)CxOy) dispersed within HfO2 formed the major structure of the oxide layer. A coherent boundary with lattice distortion existed at the HfO2/(Ti, Hf)CxOy interface along the (111) crystal plane direction, which served as an effective oxygen diffusion barrier. The Hfrich oxycarbide ((Hf, Ti)CxOy) together with (Ti, Hf)CxOy, HfO2, and precipitated carbon constituted a dense transition layer, ensuring favorable bonding between the oxide layer and the matrix. The Ti content affects the oxidation resistance of (Hf, Ti)C by determining the oxide layer's phase distribution and integrity. [ABSTRACT FROM AUTHOR]

A fine-grained WC-15wt%Al0.5CoCrFeNi cemented carbide was prepared through a vacuum and gas pressure sintering. For achieving high surface integrity, diamond wheel grinding serves as the primary molding process for the machining of WC cemented carbide. To reveal the influence of grinding on the surface integrity of fine-grained WC-HEA cemented carbide, studies were conducted on grinding force, surface microstructure, surface roughness, residual stress, microhardness, and bending strength. The morphological analysis of the ground surface indicated a transition in the material removal mechanism of WC-HEA cemented carbide from ductile removal to brittle removal, with brittle removal becoming predominant as the depth of grinding increases. With the increasing depth of grinding, the grinding force increases, and the grinding force increases while the surface roughness decreases. Correspondingly, there is an improvement in both hardness and bending strength. Additionally, grinding induces high residual compressive stress on the surface, with a maximum compressive stress of 1795 MPa. The bending strength of the material is found to be dependent on the residual stress. [ABSTRACT FROM AUTHOR]

A combination of X-ray diffraction and X-ray fluorescence analysis has shown that the strengthened layer formed during electric spark alloying of 65G steel with a processing electrode made of the T15K6 hard alloy is a nanocrystalline material, the ratio of the crystalline and amorphous phases in which is achieved by changing the discharge energy. Since an increase in discharge energy leads to an increase in surface roughness and its amorphization, there is an optimal value of discharge energy at which maximum wear resistance of the resulting nanocomposites is achieved. At E = 0.2 J, the wear resistance of the hardened layer is 7–10 times higher than the wear resistance of the untreated surface. [ABSTRACT FROM AUTHOR]

Hafnium carbide (HfC) is a refractory compound known for its exceptional mechanical, thermal, and electrical properties. This compound has gained significant attention in materials science and engineering due to its high melting point, extreme hardness, and excellent thermal stability. This study presents crystal structure prediction via energy landscape explorations of pristine hafnium carbide supplemented by data mining. Apart from the well-known equilibrium rock salt phase, we predict eight new polymorphs of HfC. The predicted HfC phases appear in the energy landscape with known structure types such as the WC type, NiAs type, 5-5 type, sphalerite (ZnS) type, TlI type, and CsCl type; in addition, we predict two new structure types denoted as ortho_HfC and HfC_polytype, respectively. Moreover, we have investigated the structural characteristics and mechanical properties of hafnium carbide at the DFT level of computation, which opens diverse applications in various technological domains. [ABSTRACT FROM AUTHOR]

Carbide tools are extensively used in the automotive, aerospace, and marine industries. However, an unsuitable tool-edge treatment can affect the cutting performance of carbide tools. In the tool-cutting process, the cutting edge radius is one of the major factors that affect the cutting force, temperature, and quality. In this study, a cutting simulation model of carbide inserts was used to analyze the effect of the cutting edge radius on the cutting performance. The cutting edge radii of the inserts were prepared using shear-thickening polishing methods, followed by cutting experiments. The accuracy of the cutting simulation model was verified through cutting experiments. The simulation results showed that under low-speed cutting conditions, the cutting force and temperature tended to increase with an increase in the cutting edge radius, and the cutting temperature was less affected by the cutting edge radius. The results of the cutting force and cutting temperature obtained from the experiment and simulation were consistent; therefore, the cutting simulation model was verified to be reliable. The results indicate that modeling cutting simulation is a promising research method for predicting the cutting performance of tools. [ABSTRACT FROM AUTHOR]

Doping rare earth elements in WC-Co cemented carbide can make the additives and the original elements form a complex structure, thus further strengthening the overall structure and improving the comprehensive properties of cemented carbide. In this paper, the rare earth element La is added to the cemented carbide WC-Co. Through the construction of atomic cell and interface, the influence of La element on WC-Co cemented carbides is analyzed. The influence law of La atom on other atoms is explained according to analyze the adhesion work, reaction enthalpy, electronic state density and charge density. The results show that more covalent bonds are generated near lanthanum atoms at the interface junction, which enhances the interface bonding strength, makes the whole structure more stable, and the unit cell doped with La element has better stability and improves the overall toughness. The calculation results can provide data for enhancing the performance of cemented carbides and provide a theoretical basis for doping rare earth lanthanum in WC-Co cemented carbides in the future. [ABSTRACT FROM AUTHOR]

In this work, a number of geometrical parameters related to the microgeometry of the cutting edge, such as rounding radius r, maximum clearance wear VBmax and a number of others, were determined. Tools for processing wood materials made of WC-Co cemented carbide with a PVD coating based on Ti and Al. were blunted until the wear indicator VBmax reached the value of 0.2 mm. The cutting blades prepared in this way were tested using a contact profilometer. Based on the data obtained in this way, an analysis of the blade contour over a length of 10 mm was carried out in the AutoCad environment. This section included both the blunted part and the part not involved in the cutting process. Correlations obtained using a procedure written in Visual Basic for Applications using elements of statistical data analysis built into the Excel program, between the selected rounding asymmetry coefficients denoted with letter K and the blade wear indicators proposed in the tests were analyzed. Geometric indicators were also determined, taking into account the working conditions of the tool, affecting the process of its blunting, such as e.g. h (uncut chip thicknesses). [ABSTRACT FROM AUTHOR]

Macrosegregation and coarse primary carbides caused by microsegregation are typical solidification defects during Vacuum Arc Remelting (VAR) which greatly limit the mechanical properties of M50-bearing steel components. A solid-liquid Eulerian two-phase model that describes solidification behaviors at both macro and micro scales is developed to predict macrosegregation of M50 ingots under a complex multi-physics condition. A good match is observed between the simulated results and experimental data. The segregation pattern of carbon is predicted with and without natural convection. Compared with thermal-solutal buoyancy, the Lorentz force is stronger and regarded as the main driving force for macrosegregation formation. The flows generated by thermal-solutal buoyancy and Lorentz force are in opposite directions. The natural convection flowing downward along solidification front leads to more serious positive segregation at the center of ingot. The uniformity of concentration distribution is improved with the increase of ingot diameter. The main reason is that the increase of diameter leads to the decrease of current density, and further decreases the Lorentz force, thus weakening the fluid flow. For the first time, an analytical formula of the equivalent size of primary carbides in M50 steel is established. It is found that the size of carbides in large-diameter industrial VAR-ingot is larger. The present work provides new insights for co-operative controlling the macro and micro segregations and the size of carbides in VAR ingots. The optimal ingot size with a diameter of 280 mm is found. [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]

Despite its unique physicochemical properties, the catalytic application of nickel carbide (Ni3C) in organic synthesis is rare. In this study, we report well‐defined nanocrystalline Ni3C (nano‐Ni3C) as a highly active catalyst for the selective hydrogenation of nitriles to primary amines. The activity of the aluminum‐oxide‐supported nano‐Ni3C (nano‐Ni3C/Al2O3) catalyst surpasses that of Ni nanoparticles. Various aromatic and aliphatic nitriles and dinitriles were successfully converted to the corresponding primary amines under mild conditions (1 bar H2 pressure). Furthermore, the nano‐Ni3C/Al2O3 catalyst was reusable and applicable to gram‐scale experiments. Density functional theory calculations suggest the formation of polar hydrogen species on the nano‐Ni3C surface, which were attributed to the high activity of nano‐Ni3C towards nitrile hydrogenation. This study demonstrates the utility of metal carbides as a new class of catalysts for liquid‐phase organic reactions. [ABSTRACT FROM AUTHOR]

Cemented carbide used in the rotor of a mud pulser is subjected to the scouring action of solid particles and corrosive mud media for a long time, which causes abrasive wear and electrochemical corrosion. To improve the wear and corrosive resistance of cemented carbide, samples with different cobalt content (WC-5Co, WC-8Co, and WC-10Co) receive deep cryogenic treatment (DCT) at −196 °C for 2.5 h. An optical metalloscope (OM) and X-ray diffractometer (XRD) are used to observe the phase changes of cemented carbides, and the XRD is also used to observe the change in residual stress on the cemented carbide's surface. A scanning electron microscope (SEM) is used to characterize the wear and electrochemical corrosion surface microstructure of cemented carbides (untreated and DCT). The results show that the DCT promotes the precipitation of the η phase, and the diffraction peak of ε -Co tends to intensify. Compared with the untreated, the wear rates of WC-5Co, WC-8Co, and WC-10Co can be reduced by 14.71%, 37.25%, and 41.01% by DCT, respectively. The wear form of the cemented carbides is mainly the extrusion deformation of Co and WC shedding. The precipitation of the η phase and the increase in WC residual compressive stress by DCT are the main reasons for the improvement of wear resistance. The electrochemical corrosion characteristic is the dissolution of the Co phase. DCT causes the corrosion potential of cemented carbide to shift forward and the corrosion current density to decrease. The enhancement of the corrosion resistance of cemented carbide caused by DCT is due to the Co phase transition, η phase precipitation, and the increase in the compressive stress of cemented carbide. [ABSTRACT FROM AUTHOR]

Enhancing the piezoresistivity of polymer‐derived silicon oxycarbide ceramics (SiOCPDC) is of great interest in the advancement of highly sensitive pressure/load sensor technology for use in harsh and extreme working conditions. However, a facile, low cost, and scalable approach to fabricate highly piezoresistive SiOCPDC below 1400 °C still remains a great challenge. Here, the fabrication and enhancement of piezoresistive properties of SiOCPDC reinforced with β‐SiC nanopowders (SiCNP) through masked stereolithography‐based 3D‐printing and subsequent pyrolysis at 1100 °C are demonstrated. The presence of free carbon in SiCNP augments high piezoresistivity in the fabricated SiCNP‐SiOCPDC composites even at lower pyrolysis temperatures. A gauge factor (GF) in the range of 4385–5630 and 6129–8987 with 0.25 and 0.50 wt% of SiCNP, respectively is demonstrated, for an applied pressure range of 0.5–5 MPa at ambient working conditions. The reported GF is significantly higher compared to those of any existing SiOCPDC materials. This rapid and facile fabrication route with significantly enhanced piezoresistive properties makes the 3D‐printed SiCNP‐SiOCPDC composite a promising high‐performance material for the detection of pressure/load in demanding applications. Also, the overall robustness in mechanical properties and load‐bearing capability ensures its long‐term stability and makes it suitable for challenging and severe environment applications. [ABSTRACT FROM AUTHOR]

The present study investigates the milling of Inconel 718 (IN718) alloy fabricated using laser powder bed fusion (LPBF). Finish milling has been performed using Al-rich ternary-coated end mills under different lubri-coolant environments. An indigenously developed Cryo-MQL technology for greener manufacturing has been employed. Machinability results have been evaluated in terms of milling forces, tool wear progression, wear mechanisms, surface roughness, sub-surface damages and chip characteristics. MQL and Cryo-MQL conditions reduced milling forces by 50.6% and 47.2%, respectively. A 35–67% flank wear reduction has been obtained for the Cryo-MQL, resulting in minimal sub-surface deformation. Cryo-MQL caused the least milling-induced deformation with no transverse microcrack due to an excellent balance of cooling and lubrication actions. Micro-hardness of the machined sub-surface ranged 450–490 HV0.03 (100–400 μm) for Cryo-MQL compared to 435–485 HV0.03 in a deeper sub-surface deformation zone (250–450 μm) for dry milling. The synergy of lubri-coolant actions in Cryo-MQL mitigated frictional tracks, chip-side cracking and chip-edge fracture. [ABSTRACT FROM AUTHOR]

Cracking resistance is vital to the practical application of spring steels, which consists of fracture toughness (KIC) under the quasistatic loading condition and fatigue crack propagation (FCP) resistance under the cyclic loading condition. In the present study, the relation between the KIC/FCP resistance and microstructure of the 50CrMnSiVNb spring steel tempered at various temperatures is studied. In the results, it is shown that the dislocation density is the main factor influencing the KIC and FCP resistances, and the carbide size/quantity and morphology can also affect the KIC and FCP resistances. Thus, reducing the dislocation density is the most effective method to enhance the cracking resistance of the investigated steel. Moreover, decreasing the aspect ratio and obtaining a moderate size of tempered carbides are also beneficial to the cracking resistance. In addition, free hydrogen atoms can cause intergranular fracture on the fracture surface, worsening the FCP rate. To enhance the FCP resistance, smelting processes need to be improved to reduce the hydrogen content of the investigated steel. [ABSTRACT FROM AUTHOR]

A transverse static magnetic field (TSMF) is implemented in a laboratory electroslag remelting (ESR) experiment to control eutectic carbides morphology of Cr8 die steel herein. Under action of a TSMF, the temperature distribution of the molten pool becomes homogeneous, the local solidification time is shortened, and the interdendritic region space shrinks, which result in an evenly spaced distribution of solute atoms and a reduction in interdendritic segregation. Therefore, the formation and subsequent growth of eutectic carbides are further inhibited, thereby causing the generation of smaller and more uniform distributed eutectic carbides due to the application of the TSMF. Moreover, the increase of the number of Al2O3–(Ti,V)N inclusions serves to be the heterogeneous nucleus of carbides (inclusions also become finer) caused by TSMF, which also contributes to the refinements of eutectic carbides in Cr8 ingots. [ABSTRACT FROM AUTHOR]

The morphology of carbides, the distribution of alloying elements, and the dissolution of primary carbides in 6Cr13 continuous casting slabs during the high‐temperature homogenization process are studied herein. The results show that severe segregation of alloying elements exists at the center of the cast slabs, accompanied by large, interconnected primary carbides in the form of a network. Large‐sized reticulated primary carbides are difficult to completely dissolve and eliminate during homogenization treatments. Large‐sized primary carbides will dissolve along the contours and the joints between the carbides when the temperature of high‐temperature homogenization does not exceed 1250 °C and the time does not exceed 1 h. The carbides that had broken off will precipitate again along the original contour in the form of large‐sized brain‐like carbides beyond this temperature and time. In situ observation of the high‐temperature homogenization process reveals that when the slab is heated to 1200 °C, the local liquid phase starts to be generated around the carbide. Cr atoms diffuse into the matrix through the liquid–matrix interface; it will accelerate the high‐temperature homogenization process and improve the segregation of alloying elements around carbides. [ABSTRACT FROM AUTHOR]

Prolonging the life of hot stamping dies in the automotive industry is challenging. Surface modification is an effective way to improve the durability of the dies. In this study, two tool steel grades, one cold work tool steel (V4E) and one high‐boron tool steel (HBS), are deposited on a tool steel substrate using directed energy deposition, followed by tempering. Softening behavior at high temperatures of 550 and 600 °C is investigated. In the key findings, it is revealed that both steels exhibit remarkable hardness, surpassing the substrate even after extended exposure to high temperatures. HBS shows excellent softening resistance in terms of hardness at 550 °C but experiences a significant drop at 600 °C. V4E demonstrates an overall superior softening resistance due to its thermal stable MC (M represents metal) carbides and the relatively stable dislocation density. Microstructural analysis highlights some unique features, such as borides in HBS and dendritic structures in V4E. In this study, the correlation between microstructure characteristics and hardness evolution is revealed, providing some insights into how these materials resist softening to enhance the longevity and performance of hot stamping dies. [ABSTRACT FROM AUTHOR]

Two chromium-rich carbide hard-faced plates, alloy—A and alloy—B, were subjected to a 3-body dry sand abrasion test. The difference was in the coating microstructure. Alloy-A contains globular chromium carbide (M7C3 type) in the austenite matrix, whereas alloy—B is composed of a banded structure with an alternate layer of carbide and austenite. Alloy B showed a superior abrasion resistance (nearly 40%) than alloy—A. A detailed microstructural investigation was made on the abraded surface. The higher abrasive wear resistance of alloy-B was attributed to the coating morphology, the composite-like microstructure resulted in an effective strain distribution among the austenite matrix and carbides. This postulate was supplemented by higher average misorientation, which was observed at sub-surface regions of the worn-out specimen, leading to form a strain-induced martensite. However, in alloy—A, the abraded surface contained abundant broken carbides. [ABSTRACT FROM AUTHOR]