TaC Addition Research Articles

Insights into hardening and strengthening in ultrafine Ti(C, N)-based cermets

Ultrafine Ti(C, N)-based cermets are vacuum-sintered by refining the particle size of raw materials and tailoring the WC/TaC ratio to achieve the improvements in comprehensive mechanical properties and cutting performance. The hardness, flexural strength and tool lifespan of ultrafine Ti(C, N)-based cermets are substantially higher than those of submicron Ti(C, N)-based cermets with the same composition because of the refined grains and the improved distributions of both metal phases and residual stress. The hardness attenuation behavior and strengthening mechanism in Ti(C, N)-based cermets at different test temperatures have been proposed. At 400 ℃, the hardness attenuation of Ti(C, N)-based cermets depends mainly upon the softening of metal phases. However, at 800 ℃, the hardness attenuation of Ti(C, N)-based cermets is mainly related to the reduced bearing capacity of hard ceramic phases and interfacial sliding. The addition of refractory TaC is beneficial for the improvement of high-temperature mechanical properties and the tool lifespan, attributed to the strengthening of the ceramic framework by tantalum atoms.

Preparation of an additive using tannic acid for enhancing rheological properties of coal-water slurry

ABSTRACT Low-rank coal is an ideal future development coal for coal-water slurry (CWS) due to its abundant resource, but low-rank coal is tougher to produce slurry than high-rank coal. Herein, a new-type macromolecular additive, tannic acid grafted carboxymethyl cellulose sodium (TAC), was designed and prepared to enhance the rheological properties of CWS using Hongshaquan coal in Xinjiang (Coal-HSQ). This work shows that trace amounts of TAC can effectively improve the fluidity of CWS in comparison with calcium lignosulfonate (CLS). Through contact angle and a novel surface characterization method in this field called microscopic infrared imaging, the analyses reveal the hydrophobicity of the Coal-HSQ surface modified by TAC is improved, which is beneficial for enhancing the fluidity of CWS. The apparent viscosity of CWS can be reduced to the lowest point (674.8 mpa·s), as CWS slurry concentration is 55 wt% and TAC addition is only 0.2 wt%. Finally, the highest slurry concentration of CWS prepared with 0.2 wt% TAC can be increased to 56.3 wt%.

Grain growth behavior in TaC-modified ultrafine Ti(C, N)-based cermets

Revealing the grain growth behavior during liquid phase sintering is of great significance for scientific application of grain growth inhibition strategies and the regulation of microstructure. In this study, the effects of both TaC addition and the particle size of starting materials on microstructure of Ti(C, N)-based cermets were investigated. Ultrafine Ti(C, N)-based cermets modified with TaC addition exhibit an obvious grain growth of grey phase during liquid phase sintering. The grain growth of grey phase is typically controlled by liquid-phase diffusion, with the grain growth index of 3 and activation energy of 48–66 kJ/mol. In particular, the increase in grain contiguity of grey phase caused by the evaporation of metal liquid phase at high temperatures, faceted transition of grey phase grains, and the loss of carbon and nitrogen are considered to be the main reasons for the decrease in the grain growth rate of grey phase at high temperatures.

The synergetic effect of TaC particles and Re alloy on microstructure and mechanical properties in tungsten alloy

TaC enhancement particles and Re alloy were used to improve the strength and ductility of the tungsten alloy. The synergetic effect of TaC addition and Re alloying on relative density, microstructure, and mechanical properties of tungsten alloy were investigated. The results indicated that a W-based composite with 2.5 wt% TaC addition and 25 wt% Re alloying exhibited yield stress of 1.23 GPa, the ultimate compressive stress of 2.86 GPa, bending strength of 1.30 GPa and strain capacity of 42 %, which was increased by 114 %, 140 %, 226 %, and 133 % than those of pure W. Further analysis revealed that the grain boundary purification, grain refinement, and kinematic strain gradient contribution because of the addition of TaC, lattice distortion, and the generation of dislocations because of the addition of Re alloying are the main strengthening mechanisms in W–TaC-Re composite.

Effect of TaC and graphene nanoplatelets on the microstructure and mechanical properties of ZrB2

In this experiment, in order to investigate the effect of TaC addition on the microstructure, densification and mechanical properties of ZrB2 composites reinforced with graphene nanoplatelets (GNP), three composites were fabricated via spark plasma sintering (SPS) at 1900 °C. Relative density was determined by Archimedes method. The XRD and EDS analyses were used to explore the phase composition and elemental distribution. Also, Field emission scanning electron microscopy (FE-SEM) was employed to characterize the microstructure (grain size and porosity). Flexural strength, fracture toughness and hardness were determined by three-point bending test, single-edge notched beam (SENB) and macro and micro Vickers methods, respectively. The results showed that the presence of the GNP, alone and combined with TaC, increases the relative density sharply to 99.6 %. In addition, full densification occurred by the addition of 10 and 20 vol% TaC compared to the monolithic ZrB2 ceramic with 83 % relative density. Maximum flexural strength and fracture toughness of 580 MPa and 4.5 MPa.m0.5 were obtained, respectively, for ZrB2- GNP and ZrB2- GNP doped with 10 vol% TaC.

Orthogonal Experimental Optimization of Preparation and Microstructural Properties of a Diffusion Barrier for Tantalum-Based Silicide Coatings.

To solve the problem of silicide coatings on tantalum substrates failing due to elemental diffusion under high-temperature oxidation environments and to find diffusion barrier materials with excellent effects of impeding Si elemental spreading, TaB2 and TaC coatings were prepared on tantalum substrates by the encapsulation and infiltration methods, respectively. Through orthogonal experimental analysis of the raw material powder ratio and pack cementation temperature, the best experimental parameters for the preparation of TaB2 coatings were selected: powder ratio (NaF:B:Al2O3 = 2.5:1:96.5 (wt.%)) and pack cementation temperature (1050 °C). After diffusion treatment at 1200 °C for 2 h, the thickness change rate of the Si diffusion layer prepared using this process was 30.48%, which is lower than that of non-diffusion coating (36.39%). In addition, the physical and tissue morphological changes of TaC and TaB2 coatings after siliconizing treatment and thermal diffusion treatment were compared. The results prove that TaB2 is a more suitable candidate material for the diffusion barrier layer of silicide coatings on tantalum substrates.

β→α Phase Transformation and Properties of Solid-State-Sintered SiC Ceramics with TaC Addition.

Dense SiC-based composite ceramics were fabricated by means of the ex situ addition of TaC using solid-state spark plasma sintering (SPS). Commercially available β-SiC and TaC powders were chosen as raw materials. Electron backscattered diffraction (EBSD) analysis was conducted to investigate the grain boundary mapping of SiC-TaC composite ceramics. With the increase in TaC, the misorientation angles of the α-SiC phase shifted to a relatively small range. It was deduced that the ex situ pinning stress from TaC greatly suppressed the growth of α-SiC grains. The low β→α transformability of the specimen with the composition of SiC-20 vol.% TaC (ST-4) implied that a possible microstructure of newly nucleated α-SiC embedded within metastable β-SiC grains, which could have been responsible for the improvement in strength and fracture toughness. The as-sintered SiC-20 vol.% TaC (ST-4) composite ceramic had a relative density of 98.0%, a bending strength of 708.8 ± 28.7 MPa, a fracture toughness of 8.3 ± 0.8 MPa·m1/2, an elastic modulus of 384.9 ± 28.3 GPa and a Vickers hardness of 17.5 ± 0.4 GPa.

Effect of TaC Content on Microstructure and Properties of W-TaC Composites

Transition metal carbide reinforcement can improve the performance of pure W. W-(10-50) vol% TaC composites were prepared by spark plasma sintering at 2100 °C. The effect of TaC content on the microstructure, mechanical properties, and thermal conductivity of the composites was studied. The ablation resistance of the W-TaC composites was evaluated under an air plasma torch. The addition of TaC into the W matrix enhanced the densification of W-TaC composites, the density of W-40 vol% TaC composite exceeded 93%. TaC particles inhibited the growth of W grains during sintering. Reactive diffusion occurred between W and TaC, forming the solid solutions of (W,Ta)ss and (Ta,W)Css. W and TaC react to form the W2C phase at a TaC content of 50 vol%. The Vickers hardness of the composite increases from 3.06 GPa for WTA1 to 10.43 GPa for WTA5. The flexural strength reached 528 MPa in the W-40 vol% TaC composite. The thermal conductivity of W-20 vol% TaC composite was 51.2 ± 0.2 W·m-1·K-1 at 750 °C. The addition of TaC improved the ablation resistance of W-TaC composites. The mass ablation rate of W-30 vol% TaC composite was 0.0678 g·s-1. The ablation products were mainly W oxides and complex oxides of W-Ta-O.

Effect of TiC Content and TaC Addition in Substrates on Properties and Wear Behavior of TiAlN-Coated Tools

The present paper reports a new way to improve the wear resistance of coated carbide tools by increases in TiC content and the addition of TaC in substrates. The results suggest that the average grain size of the substrate increased with the increases in TiC (0–14 wt.%) content, and the hardness of the TiAlN coating deposited on the substrate exhibits a similar trend. In addition, the adhesion strength of the TiAlN-coated carbide increases with increasing TiC content, which can be attributed the formation of the (Ti,W)C phase and the similar hardness of the substrate and coating. The addition of TaC into the substrates inhibits the grain growth and thereby causes the hardness and adhesion strength of the TiAlN coatings to improve from 24.6 GPa and 16.7 N to 30.1 GPa and 17.3 N, respectively. In turning tests, the TiAlN coating deposited on the substrates with the TaC addition achieved the best wear resistance in turning stainless steel because it possessed the highest substrate and coating hardness and sufficient adhesion strength. However, the TiAlN coating deposited on the substrates with a higher TiC content shows the better wear resistance in turning titanium (TC4), which can be attributed to it having the highest adhesion strength.

Hot-pressed ZrB2–SiC composite ceramics: Effect of various Ta-containing additives on the microstructure and mechanical properties

The ZrB2–SiC composites have been commercially used at ultrahigh temperatures, but it often failed due to their poor toughness. In order to solve this problem, four types of Ta-containing additives (Ta, TaC, TaB2 and TaSi2) were used as the “third phase” to regulate the microstructure, so as to enhance the mechanical properties of hot-pressed ZrB2–20SiC-based ceramics (in vol. %). The incorporation of the additives generated a core–shell structure, which comprised of a ZrB2 core and a (Zr, Ta)B2 solid solution shell. The additives helped refine the ZrB2 grains in addition to the metallic Ta and release the internal stress field generated by the thermal misfit. The interfacial structure was modified by the formation of the coherent core/shell interface and the semi-coherent interface of adjacent ZrB2 grains and the semi-coherent ZrB2/(Zr, Ta)C interface in the TaC-additive composite. The addition of TaB2 or TaC hardened the ZrB2–20SiC ceramics, whereas the addition of Ta or TaSi2 reduced the hardness. The fracture toughness was enhanced by the formation of the Ta-containing phases. These phases reduced the stress intensity factor of the crack tip, which was proportional to the intrinsic residual stress. However, the crack-propagation mechanism would be changed by the incorporation of various Ta-containing additives. The decrease in the crack deflection, which was induced by the stronger interfacial bonding force and the significant consumption of SiC, resulted in relatively low toughness in the Ta- and TaC-included samples. The weaker interfacial bonding force in the TaB2- and TaSi2-included samples caused an increase in deflection and generated branching, which enhanced the toughness of the TaSi2-included composites to ∼4.72 MPa⸱m1/2.

Low‐temperature synthesis and oxidation resistance of random combination of Hf, Nb, and Ta carbides microcuboids

AbstractBased on the dissolution‐precipitation mechanism, this article successfully synthesized binary and ternary transition metal carbide microcuboids with random combinations of Hf, Nb, and Ta by annealing monocarbides/cobalt powders. Accelerated mass transport rate through the flow of molten alloys (Co‐Hf‐Nb‐Ta) instead of slow solid diffusion made the low‐temperature pressureless sintering technique (1500°C) a reality. Furthermore, the equilibrium morphology was driven by the gradient Gibbs potential of carbides induced by the different local curvature of powders and anisotropic interfacial energy. (Hf0.5Ta0.5)C possessed the optimal oxidation resistance among all mentioned carbides, even competed with (Hf1/3Nb1/3Ta1/3)C. During the isothermal oxidation at 800∼1200°C, the doping of Nb and Ta in carbides assisted the monoclinic‐orthorhombic HfO2 transition at ambient pressure, besides, TaC can also restrain the orthorhombic‐monoclinic transition of Nb2O5. Moreover, oxidation kinetics parameters concluded that the addition of HfC and TaC contributed to the decreasing reaction order and the increasing activation energy, respectively.

Effect of TaC Addition in Substrates on Microstructure, Properties and Cutting Behavior of TiAlN/WC-TiC-Co Coated Tools

Effect of TaC Addition in Substrates on Microstructure, Properties and Cutting Behavior of TiAlN/WC-TiC-Co Coated Tools

Structure formation and properties of WC-(W,Ti)C-Ti(C,N)-TaC-Co gradient cemented carbides with cubic phases free in the surface layer

In this paper, gradient cemented carbides with the cubic-phase free in the surface layer were prepared, and the compositional gradient formation was explored. The relations between the properties of the gradient cemented carbide and the TaC addition were investigated. The results showed that the inward Ta migration during the gradient-structure formation of the cemented carbide WC-Co-(W,Ti)C-Ti(C,N)-TaC-W was mainly driven by the thermodynamic coupling between Ta and Ti. The thickness of the cubic-phase free layer decreased as the total Ta/C ratio is enlarged in the gradient cemented carbide. With TaC added in the gradient cemented carbide, the undissolved Ti(C,N) cores was rarely observed in the bulk owing to the solid solution of Ta. The average sizes of WC phases and (W,Ti)C phases could be reduced by the TaC addition, but hardly refined further when TaC exceeds its solubility in the binder. All of the transverse rupture strength, the hardness and the fracture toughness increased with the low TaC content but decreased with the high TaC content. The coercive force was elevated with TaC added in the gradient cemented carbide, and the magnetic saturation increased when increasing TaC contents. Additionally, the coercive force was raised while the magnetic saturation fell down after the cubic-phase free layer was removed.

Effect of TaC particles on the microstructure and oxidation behavior of NiCoCrAlYTa coating prepared by electrospark deposition on single crystal superalloy

NiCoCrAlYTa/TaC metal matrix composite coatings were prepared on single crystal superalloy (SX) using electrospark deposition (ESD) to improve its high temperature performance. The effect of TaC addition on the coating microstructure, oxidation behavior, wear resistance and physical properties of electrode were investigated. The results showed that, with the addition of TaC particles, the density of electrode increased, while the thermal conductivity and thermal diffusivity decreased. In the electrode, TaC particles were distributed around or embedded into the NiCoCrAlYTa powders, while in ESD coatings, they were distributed homogeneously in both dendrite cores and interdendritic regions. The generation of β-NiAl phase in ESD coating was prevented by adding TaC particles. During 1000 °C/100 h oxidation, the mass gain of coating with TaC addition was lower than that without TaC addition during the first 40 h, and then became higher. The oxidative products were similar, except that θ-Al2O3 was relatively more in coating without TaC, while Y3Al5O12 was more in coating with TaC addition. The microhardness and wear resistance in both coatings decreased after oxidation, however, it was on the same level for NiCoCrAlYTa coating before oxidation and NiCoCrAlYTa/TaC coating after oxidation. Thus, the overall high temperature performance of the coatings was improved due to the addition of TaC particles.

Effect of the combined addition of TaC and NbC on the dispersity of cubic phase in ultra-fine WC–10Co–0.5Cr cemented carbides

TaC and NbC have different effects on the dispersity of precipitated cubic phase, which acts as an important role in regulating the mechanical properties of ultra-fine cemented carbides. In this work, the influence of the combined addition of TaC and NbC on the microstructure evolution and mechanical properties in ultra-fine WC–10Co–0.5Cr cemented carbides was systematically investigated through the thermodynamic calculations and experiments. With the guide of thermodynamic calculations, the ultra-fine WC–10Co–0.5Cr cemented carbides with the combined addition of TaC and NbC were prepared. By replacing TaC with NbC, the dispersity of cubic carbides can be improved significantly from large-size honeycombed to small-size isolated cubic particles, which is explained by thermodynamic calculations. The brittle cubic phase results in the degradation of crack propagation resistance, and thus deteriorates the mechanical properties. Therefore, both the hardness and fracture toughness increase with the improvement of dispersity of cubic phase in cemented carbides.

Pressureless sintering of WC-TaC binderless carbide

Binderless carbides (WC-(0–10)wt.%TaC) were prepared via pressureless sintering at a relatively low temperature of 1850 °C using micro-scaled initial powders. The phase evolution, microstructures, physical and mechanical properties, and densification behaviors of these materials were investigated. The results showed that the binderless carbides had a single WC phase regardless of TaC addition. TaC dissolved into WC, resulting in the lattice expansion of the latter. With the increase in TaC addition up to 10 wt%, the lattice parameters, a and c, of hexagonal WC, as calculated using the Nelson–Riley extrapolation method, increased from 0.290963 nm to 0.284075 nm–0.291838 nm and 0.284929 nm, respectively. The proper addition of 2.5 wt% of TaC inhibited the coalescence of the WC particles and resulted in a homogeneous grain size. Furthermore, the dissolution of TaC improved the sinterability and facilitated densification, resulting in a low porosity of A02B02C00. The increase in TaC addition mitigated the mechanical properties owing to the decrease in sinterability, increase in porosity, and abnormal grain growth. Hence, almost full densification of binderless carbide was successfully consolidated at 1850 °C. The Vickers hardness of 26.51 GPa and fracture toughness of 9.95 MPa m1/2 achieved approached the corresponding levels of binderless carbides prepared via pressure-assisted sintering.

Pressureless sintering and properties of boron carbide composite materials

AbstractBoron carbide and Tantalum boride composites were prepared by pressureless sintering of B4C with addition of TaC powder. The effect of TaC addition on the sinterability of boron carbide was studied. High densified ceramic with a relative density of 98.7% was obtained at sintering temperature of 2250°C. The composition and the microstructure of the dense composites are characterized by means of x‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectroscopy (EDX). The studies show that the composites contain boron carbide, TaB2, and carbon phases with a homogeneous structure. In addition, the correlation between the composition and the electrical conductivity was investigated. The electrical conductivity of the composite increased with increasing addition of TaC, and a change in conduction behavior from semiconducting to metallic was observed. High hardness value of 28.49 ± 1.33 GPa was obtained by the sample with 30 wt% TaC addition.

Effects of TaC addition on microstructure and mechanical properties of SiBCN composite ceramics

In this work, SiBCN–TaC composite ceramics were prepared by a combination of mechanical alloying and reactive hot-pressing sintering techniques. The effects of TaC addition on microstructure, mechanical properties and oxidation resistance of the resulting composite ceramics were studied in detail. Results suggested that the as-sintered SiBCN–TaC composite ceramics composed of three phases: SiC, BN (C) and TaC. Some TaC~10–20 nm dispersed randomly within the ceramic matrix while others ~3–5 nm were scattered in turbostratic BN(C). The introduction of nanocrystalline TaC can effectively improve the flexural strength and fracture toughness of SiBCN ceramics. The incorporation of 10 wt% TaC showed the optimized mechanical properties with flexural strength and fracture toughness reaching to 399.5 MPa and 4.26 MPa m1/2 respectively. The TG-DTA analysis confirmed the oxidation damage of BN (C) phase can be effectively alleviated by the introduction of TaC nanocrystals.

Effects of TaC and TiC addition on the microstructures and mechanical properties of Binderless WC

WC ceramics were sintered using a resistance-heated hot-pressing machine in the temperature range of 1600–1800 °C for TaC addition and at 1800 °C for TiC addition. Dense WC ceramics containing 0–2 mol% TaC at 1800 °C, 1–2 mol% TaC at 1700 °C, and 0–6 mol% TiC were obtained. A small addition of 1–2 mol% TaC at 1700 °C improved the sinterability of WC. The W2C- and TaC-type solid solutions, (W, Ta)2C and (Ta, W)C, were produced during the sintering process. The added TaC and TiC fully changed to the solid solutions of (Ta, W)C for dense TaC-added WC ceramics and (Ti, W)C for TiC-added WC ceramics. TiC inhibited the grain growth of WC in WC ceramics. The hardness of TaC-added WC ceramics sintered at 1700 °C increased from 19 GPa with no TaC addition to 25.1 GPa with 1 mol% TaC. The hardness of TiC-added WC ceramics sintered at 1800 °C differed only slightly from that without TiC addition, ~24 GPa. The relationship between the hardness of dense TaC- and TiC-added WC ceramics and WC grain size was similar to that for pure WC. The fracture toughness of the TaC-added WC ceramics at 1700 °C increased from 5.7 MPa m0.5 without TaC addition to 6.7 MPa m0.5 at 1 mol% TaC.

Microstructure evolution, mechanical properties and strengthening mechanism of refractory high-entropy alloy matrix composites with addition of TaC

This study focuses on novel refractory MoNbRe0.5W(TaC)x high-entropy alloy matrix composites synthesized by vacuum arc melting. The microstructure evolution, compressive mechanical properties at room temperature and strengthening mechanism of the composites with addition of TaC are analyzed and discussed. The MoNbRe0.5W(TaC)x composites consist of a BCC solid solution as the matrix and an eutectic microstructure (BCC and multi-component carbide (Mo, Nb, W, Ta)C phases) at grain boundaries. The lamellar eutectic structure would be formed from the decomposition of subcarbide (Mo, Nb, W, Ta)2C and the fully solid solubility of Re. The MoNbRe0.5W(TaC)0.5 composite has the maximum failure strain of 10.25%. The MoNbRe0.5W(TaC)0.5 to MoNbRe0.5W(TaC)0.6 composites exhibit excellent comprehensive mechanical properties, with excellent strength and reasonable ductility at room temperature. The reinforcement mechanism of the composites is dominated by precipitation and fine-grained strengthening effect. The good ductility of MoNbRe0.5W(TaC)0.5 composite is contributed to the grain refinement of the BCC matrix phase.