TaC Ceramics Research Articles

Preparation method and industrialization of Ta-based ultra high temperature ceramic Tujia jar tea baking jar materials

The production materials of traditional Tujia jar tea often face problems such as poor high-temperature performance and poor durability. To improve the temperature resistance and durability of tea baking utensils, this study proposes a new type of TaC ultra-high temperature ceramic. TaC ceramics with excellent performance were prepared through powder metallurgy technology, including high-energy ball milling to ensure uniform mixing, followed by compression molding and high-temperature sintering. The test results demonstrated excellent mechanical properties, with a maximum depth of 948.67 nm and a contact depth of 954.45 nm, proving outstanding compressive and wear resistance. The hardness reached 21.4±0.5 Gpa, and the elastic modulus was 397.2±8.7 Gpa, both of which indicate its stability under high loads. In addition, the fracture toughness was 2.8±0.2 Mpa*m1/2. At a high temperature environment of 1000 °C, the oxidation rate constant of TaC ceramics was only 0.183 mg2 *cm−4 *h, which demonstrates its excellent high-temperature stability. The development of this TaC ceramic not only strengthened the traditional production process of Tujia teapots and tea roasting teapots, thereby improving the product’s service life, but also holds potential for other industrial applications that demand ultra-high temperature stability. These contributions provide new directions for the high-temperature application of ceramic materials and bring tangible economic and technological value to related industries.

Rapid densification and mechanical properties of ultra-high-pressure sintered transition metal carbide ceramics

Densifying transition metal carbide (TMC) ceramics is challenging due to their low diffusion coefficient and strong covalent bonding. Ultra-high-pressure sintering (UHPS) is a promising technique for preparing dense ceramic materials at low temperatures, but it is underutilized in TMC ceramics. Herein, we report the successful employment of UHPS at 1500 °C for 3 min with an auxiliary pressure of 7 GPa, yielding TaC, NbC, TiC, and ZrC ceramics with relative densities of 99.3%, 98.9%, 98.2%, and 96.4%, respectively. We demonstrate that the densification mechanism of the TMC ceramic in this investigation encompasses plastic deformation and high-pressure assisted atomic diffusion. Furthermore, we determine the Vickers hardness and fracture toughness of TaC, NbC, TiC, and ZrC ceramics to be 16.5, 15.9, 24.0, and 17.7 GPa and 2.5, 2.9, 2.8, and 1.8 MPa m1/2, respectively. Moreover, with increasing temperature from room temperature to 500 °C, the hardness and elastic modulus of all four TMC ceramics gradually decrease, with the hardness declining by approximately 17–25%.

High-temperature oxidation behaviors of dense TMC (TM= Ta, Nb, Ti and Zr) ceramics in air

This study investigated the high-temperature oxidation behaviors of TMC ceramics. The results indicate that the high-temperature oxidation curves of the four TMC ceramics follow a parabolic law, suggesting a diffusion-controlled process. The activation energies for the oxidation of TaC, NbC, TiC, and ZrC ceramics are 105.4, 124.3, 169.3, and 78.7 kJ/mol, respectively, with oxidation rate constants at 1000 °C of 16.84, 40.45, 0.18, and 14.43 mg2/cm4·h for each ceramic, respectively. The temperatures at which the ceramics disintegrate into fragments in high-temperature air are 800, 800, >1000, and 600 °C, respectively. The anti-oxidation performance of the four TMC ceramics ranks as follows: TiC > TaC > NbC > ZrC. In comparison to the reported high-entropy carbide ceramics, the TiC ceramic in this study demonstrates superior anti-oxidation performance due to dense TiO2 layer formation, characterized by significantly low oxidation rates and excellent structural stability.

Microstructures and mechanical properties of functionally graded TiCN–TaC ceramics prepared by a novel layer processing strategy

Functionally graded TiCN–TaC ceramics (FGTTCs) were fabricated using a novel layer processing method based on a vacuum hot-press sintering technology. Microstructural investigations revealed a visibly layered structure for the FGTTCs with relatively flat boundaries between the neighboring layers; additionally, the layer thickness was facilely controlled. With an increase in the sintering temperature, the hardness and flexural strength of the surface and middle layers of the FGTTCs initially increased, and then decreased. The fracture toughness of the surface layer did not undergo significant changes after sintering at various temperatures, except at 1500 °C. The FGTTC sintered at 1350 °C contained uniform fine grains and simultaneously exhibited transgranular and intergranular fracture modes. Further, it presented excellent comprehensive mechanical properties, i.e., surface layer hardness = 20.28 ± 0.18 GPa, flexural strength = 1553.76 ± 22 MPa, surface layer fracture toughness = 7.29 ± 0.24 MPa m1/2. Under the same sintering conditions, our FGTTCs presented superior mechanical properties against homogeneous TiCN–TaC ceramics (HTTCs), achieving a considerably higher flexural strength (1553.76 ± 22 vs 953.35 ± 24 MPa).

Electric field assisted solid‐state interfacial joining of TaC‐HfC ceramics without filler

AbstractThe application of ultra‐high‐temperature ceramics (UHTCs) demands effective ways of joining in overcoming the problems associated with the fabrication of complex‐shaped components. In this study, we choose to investigate a new method of rapidly joining pre‐sintered TaC and HfC ceramics without any filler material using the spark plasma sintering (SPS) technique. A well‐bonded TaC–HfC interface was observed with no apparent cracking and porosity at the joint. The joining mechanisms were predominantly driven by solid‐state diffusion and localized plastic deformation. The nanomechanical properties of the TaC‐HfC joint are better than the HfC while comparable to that of the TaC. High‐load indentation (up to 200 N) results suggest that the TaC–HfC interface is stronger than the parent UHTCs with no crack propagating at the interface. Upon comparison with the parent UHTCs, the damaged area and the average crack length at the interface, reduced up to ~94% and ~56%, respectively. This study shows that the SPS technique can also apply to joining other UHTCs without any filler, resulting in the new field of developing complex components for the thermal protection system (TPS).

Crack tolerant TaC–SiC ceramics prepared by spark plasma sintering

To achieve the densification of tough tantalum carbide ceramics at low sintering temperature, we reported a preparation of TaC ceramics by spark plasma sintering with SiC as the sintering aid and graphene platelet (GPL) as the reinforcement. The effects of GPL contents on the densification, grain growth and mechanical properties of the TaC–SiC/GPL composites were evaluated. Due to the surface reactions between SiC and TaC particles, relative density of the composite increased to 99.3% at GPL content of 1.0 wt%. The GPLs wrapped around the grains and acted as barriers for mass diffusion, therefore inhibiting grain growth. The flexural strength of the composite increased at first and reached maximum value of 570 MPa at the GPL content of 1.0 wt%; the fracture toughness reached the peak value of 5.8 MPa m1/2 at the GPL content of 1.5 wt%. Bending, bridging and pullout of GPLs were considered as the main toughening mechanisms. Thus, this work provides a new guide for the fabrication of TaC ceramics with high density and high fracture strength.

Strengthened interfacial bonding and its effects on fracture mode of TaC ceramics with addition of B

TaC ceramics with 0-0.237 wt% B addition were prepared by hot pressing. The effect of B addition on the phase constitution, interfacial chemistry/bonding and mechanical properties of the TaC ceramics were investigated. Upon B addition, the elimination of O impurity and segregation of B at grain boundaries were evidenced, accompanied by an increase in bonding strength of the TaC grains, to result in a fracture mode change from intergranular to transgranular and a reduced fracture toughness. Addition of excessive B resulted in the formation of TaB2 and C within TaC ceramics. Further, TaC-TaB2-SiC composites were prepared by Si addition. Coherent bonding between TaB2 and TaC was preserved in the TaC-TaB2-SiC composites, and residual stresses due to thermal expansion mismatch of the different phases increased flexural strength and fracture toughness of the composites.

Hot pressing and oxidation behavior of ZrB2–SiC–TaC composites

A ZrB2–20 vol% SiC–5 vol% TaC ceramic was sintered through the hot pressing process. By sintering for 60 min at 1850 °C under 40 MPa in a vacuum atmosphere, an almost fully dense specimen with a relative density of 97.5% was achieved. The phase and microstructural investigations revealed that alongside the ZrB2, SiC and TaC as the starting materials, two new phases of ZrC and TaSi2 were synthesized in-situ during the hot pressing. The oxidation behavior of as-sintered hybrid composites was investigated at three temperatures in an atmospheric furnace for 1-, 4- and 10-h cycles. Parabolic oxidation rate constants of 2.25, 30.69 and 1309.70 mg2/cm4.h were calculated for the samples oxidized at the temperatures of 1000, 1400 and 1700 °C, respectively. The activation energy of 178.7 kJ/mol was kinetically calculated for the oxidation of ZrB2–SiC–TaC ceramics. Four oxidized layers on the unaffected ZrB2–SiC–TaC matrix were also detected and microstructurally characterized.

Effect of boron addition on microstructure, mechanical properties and oxidation resistance of TaC ceramics

TaC ceramics with 0.03–0.60 wt% of boron additions were prepared by hot pressing at 2100 °C for 1 h under a pressure of 40 MPa. Effects of boron content on densification, phase composition, microstructure, mechanical properties and oxidation resistance of the TaC ceramics were investigated. When the boron content was 0.12 wt% and above, full density was obtained due to reactions between boron and oxygen impurity at presence of TaC. Minor phases of TaB2 and C were formed in the 0.24 and 0.60 wt% B compositions after gas-out of the oxygen impurity. Microstructure of the TaC ceramics was refined with increasing in boron content. The TaC ceramic with 0.24 wt% of boron showed the best mechanical properties with a Vickers hardness, flexural strength and fracture toughness of 17.7 GPa, 534 MPa and 4.6 MPa m1/2, respectively. When more boron was added, interfacial bonding of the TaC grains was strengthened causing a decrease in fracture toughness. Oxidation resistance of the TaC ceramics increased with boron content. Particularly, the 0.60 wt% B composition showed a weight gain of 0.0018 g/cm2 after oxidization at 800 °C in air for 3 h.

Pressure‐enhanced densification of TaC ceramics during flash spark plasma sintering

AbstractFlash spark plasma sintering (FSPS) offers extremely high heating rates to consolidate ceramics at a short time. However, significant grain growth sometimes occurs accompanied by rapid densification. In this work, a FSPS apparatus available for applying pressure was used to sinter TaC ceramics from powder compacts without preheating. It is found that the use of a higher pressure can efficiently promote densification and retard significant grain growth. Dense bulk TaC ceramics (95.18%) with average grain size of 4.09 μm were obtained in 90 seconds under 80 MPa. Such a process should facilitate the fast preparation of refractory ceramics with fine‐grained microstructure.

Synthesis, densification, and microstructure of TaC‐TaB2‐SiC ceramics

AbstractThe usual way to prepare TaC‐TaB2 ceramics by adding B4C to TaC leads to formation of residual C, which degrades samples’ mechanical properties. To eliminate the residual C, we suggest incorporating Si together with B4C into TaC ceramics, resulting in new ultrahigh‐temperature ceramics (TaC‐TaB2‐SiC). Dense ceramics (>99%) with SiC volume fraction ranging from 15.86% to 41.04% were fabricated by reactive spark plasma sintering at 1900°C for 5 minutes. The formation of SiO2‐based transient liquid phase was evidenced by the “film” in intermediate products, which can promote densification. The fine‐grained microstructure in final products was found to be associated with the in situ formed SiC, which impeded TaC and TaB2 grains from coarsening by the pinning effect. Besides, ultrafine TaB2 grains (~100 nm) produced during the reaction and then rearranged in liquid also contributed to grain refinement. Compared to TaC‐TaB2(‐C) ceramics prepared from TaC and B4C, the acquired composites exhibit better mechanical properties, due to their fine‐grained microstructures and the elimination of residual C.

Effects of Al addition on densification, microstructure and mechanical properties of TaC-Al ceramics

Tantalum carbide ceramics containing 0.25–3.40 wt% Al as densifying aid were prepared by hot pressing at 1900 °C under 30 MPa for 60 min. Effects of Al addition on densification, phase composition, microstructure and mechanical properties of the TaC-Al ceramics were investigated. Al was an effective oxygen getter which reacted with volatile oxygen impurities such as Ta2O5 on surfaces of TaC particles to form non-volatile minor phase of Al2O3, thus slowed TaC grain growth via inhibiting the non-densifying matter transport by evaporation-condensation. When Al content was larger than the value that was needed for complete impurity reaction of 10Al + 3Ta2O5 = 6Ta + 5Al2O3, presence of Al liquid at high temperatures improved densification of the TaC-Al ceramics because Al liquid spread along the grain boundaries and wet the TaC grains. The TaC ceramic with 0.75, 1.50 and 3.40 wt% Al addition reached a relative density value of 91.6, 97.5 and 100%, respectively, with a similar average grain size of 3.5–4.8 μm. Fe impurity dissolved in Al and formed Al6Fe; slight reaction of Al with TaC formed a thin layer of Ta-Al-C compound around TaC grains. The TaC ceramic with 1.50–3.40 wt% Al additions showed good Vickers hardness, Young's modulus and flexural strength in the range of 12.4–13.2 GPa, 413–479 GPa and 532–673 MPa, respectively. Increase in oxidation resistance of TaC ceramics was observed at 600 °C in air with a few percentages of Al additions.

Effects of the second phase on the microstructure and ablation resistance of HfC coating on C/C composites

To improve the ablation resistance of HfC coating on carbon/carbon composites prepared by supersonic atmospheric plasma spraying, SiC, TaC and ZrC ceramics were added into HfC coating as the second phase. Effects of the second phase on the microstructure, interface bonding strength and ablation resistance of HfC coating were researched. The structure of HfC-SiC coating was denser and smoother than that of HfC-TaC and HfC-ZrC coatings. The dense structure, high interface bonding strength and formation of continuous Hf-Si-O glassy film resulted in the better ablation resistance of HfC-SiC coating. During ablation, the HfC-TaC coating was oxidized to a stable Hf6Ta2O17 glassy film, which could restrain the oxygen penetration. A porous HfO2-ZrO2 layer was generated on the HfC-ZrC coating after ablation, some HfO2 and ZrO2 particles may be flown away by the high-speed flame. So, the ablation resistance of HfC-ZrC coating was worse than the other two coatings.

Nano-(Ta, Zr)C Precipitates at Multigrain Conjunctions in TaC Ceramic with 10 mol% ZrC and 5 mol% Cu as Sintering Aid

A fully dense TaC ceramic was prepared by hot pressing using 10 mol% ZrC plus 5 mol% Cu as a sintering aid. Formation of (Ta, Zr)C solid solution (ss) by reaction between TaC and ZrC facilitated densification. Addition of Cu refined the microstructure and consequently improved flexural strength of the TaC ceramics. TEM investigation found ubiquitous precipitation of nanocrystallites at multigrain conjunctions. The nanocrystallites were (Ta, Zr)C solid solution with uniform dispersion in an oxygen-rich glassy matrix. Although formation of nanoprecipitates may not much affect the mechanical properties of the TaC ceramic, the structure suggested a new type of nanoceramic worth further research.

Adsorption properties and preparation of porous TaC ceramics with regular steps

Porous TaC ceramics were successfully prepared by particle packing method in order to improve the high temperature adsorption properties of ceramics. A large number of circular steps can be found clearly on the surface of the porous ceramic, and TaC ceramic particles are polycrystalline structures (fcc structure of NaCl-type). Subsequently, a porous TaC ceramics growth model was proposed to explain the formation of the steps on the ceramic surface, which revealed that the main reason for this shape was the overflow of CO and the melt of Ta2O5. Additionally, the specific surface area and median pore diameter of porous TaC ceramics were 0.098 (m2/g) and 3129 nm, respectively. And the porosity of the porous TaC ceramics was as high as 65.321%. It was impressive that the adsorption effects of porous TaC ceramics are remarkable (dropped from 4244 NTU to 0.3 NTU) and recyclable.

Polyacrylic acid, a highly efficient dispersant for aqueous processing of tantalum carbide

Polyacrylic acid (PAA) with three different molecular weights (PAA-3000, PAA-15000, PAA-100000) was used as a dispersant to investigate the aqueous dispersion behavior of commercially available TaC powder. TaC stabilized with PAA-3000 polymer showed the best dispersion behavior according to zeta potential and rheological measurements. In addition, the TaC slurry in the presence of PAA-3000 had a minimized average particle size of merely 1.08µm when dispersed in alkaline aqueous solutions. This was effective to break down any original agglomerates. A characteristic carboxylic peak was detected after adding PAA-3000 to the aqueous TaC system, using XPS analysis. Our TEM results confirmed that the surface properties of TaC were modified by the PAA-3000 dispersant. The slip-cast green body exhibits enhanced homogeneity compared to its dry-pressed counterpart. A dense TaC monolithic ceramic (>99%) was obtained after sintering. This study contributes to the understanding of advanced wet-forming techniques for TaC ceramics.

Effects of adding 5–20 mol% ZrC plus 5 mol% Cu as a sintering aid on microstructure and mechanical properties of the TaC ceramics

TaC ceramics were prepared by hot pressing at 1900°C for 30min under 30MPa mechanical pressure. Effects of the addition of 20mol% ZrC or 5–20mol% ZrC plus 5mol% Cu as sintering aids on densification, phase composition, microstructure and mechanical properties of the consolidated materials were investigated. The results showed the pure TaC had a relative density of 86%of the theoretical value. Densities >97% theoretical were reached in the materials when the sintering aids were used. ZrC and TaC reacted to form solid solutions. The grain average size decreased from 18µm in the pure TaC to 6µm at 20mol% addition. Addition of 5mol% Cu further refined the microstructures. The 20mol% ZrC+5mol% Cu and the 10mol% ZrC+5mol% Cu composition had good flexural strength of 608MPa and fracture toughness of 5.4MPam1/2, respectively.

High-strength TiB2–TaC ceramic composites prepared using reactive spark plasma consolidation

This study demonstrates that reactive consolidation achieved via spark plasma sintering (SPS) is an effective strategy to enhance the high-temperature flexural strength of TiB2-based ceramics. Monolithic ceramics of TaC and TiB2 were consolidated by non-reactive SPS and were used as reference samples. The microstructural development during room- and high-temperature strength tests was analyzed. The room-temperature strength of TiB2 ceramics was analyzed as a function of the grain size. The high-temperature strength and associated microstructural development of monolithic TaC ceramics are reported for the first time. The TiB2–TaC ceramic system was then consolidated by reactive SPS at 2000°C. The flexural strength of the 10wt% TaC–TiB2 ceramic composites reached 533MPa at room temperature and 480MPa at 1600°С. The development of the (Ti,Ta)(C,B) phase was considered the main reason for the preservation of the high strength up to 1600°С. Both bulk TaC and TiB2 exhibited drastic decreases in their bending strengths at 1600°С because of the activation of plastic deformation associated with high-temperature creep, and their strength did not exceed 210MPa.

Nano-TaC powder synthesized using modified spark plasma sintering apparatus and its densification

Using a modified spark plasma sintering apparatus, nano-tantalum carbide powder was synthesized at 1450°C by the carbothermal reduction of Ta2O5. The synthesized TaC powder had ultra-fine particle size of 62nm and a low oxygen content of about 0.5wt%. The metal basis purity of the synthesized powder was 99.94%. The particle growth during synthesis was effectively suppressed by using the modified spark plasma sintering process due to the low synthesis temperature and fast heating/cooling rate. Dense monolithic TaC ceramics were obtained by sintering the synthesized powder without sintering additives at 2200°C for 30min under 80MPa pressure. The average grain size of the dense TaC ceramics was 4μm.

Densification of tantalum carbide ceramics with 5 mol.% Al, Cu, Ag and Au

The effects of the addition of 5 mol.% aluminum, copper, silver or gold on the densification, microstructures, mechanical properties and oxidation resistance in thin air of TaC ceramics were investigated. Full density and relatively high flexural strength (up to 738 MPa) were observed in the case of the Au addition after spark plasma sintering at 1700 °C for 5 min under 30 MPa pressure. Due to wetting of the TaC grains by a thin metallic film, the consolidated materials showed enhanced oxidation resistance against thin air.