TaC Composites Research Articles

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.

Erosive wear behavior of spark plasma‐sintered SiC–TaC composites

AbstractSpark plasma sintering of SiC‐10, 20, or 30 wt% TaC composites was performed at 1800°C. Microstructures of sintered composites revealed uniform dispersion of TaC particles in SiC matrix. With the increase in TaC content, hardness decreased from 25.75 to 23.30 GPa and fracture toughness increased from 3.48 to 3.85 MPa m1/2. Erosion testing was performed to evaluate the potential of sintered composites at room temperature and 400°C by a stream of SiC particles impinging at different angles (30°, 60°, or 90°). The erosion rate varied from 25 to 166 mm3/kg, with change in TaC content, impingement angle, or temperature. The erosion rate increased as the angle of impingement and temperature increased, but reduced when the TaC concentration increased. Worn surfaces revealed that the material was dominantly removed via fracture of SiC grains and TaC particles pull‐out. SiC‐30 wt% TaC composites exhibited superior erosive wear resistance at low impingement angle and room temperature.

Comparative study of reactive and nonreactive spark plasma sintering routes for the production of TaB2‐TaC composites

AbstractThe influence of two different spark plasma sintering (SPS)‐based processing routes (i.e., reactive SPS [RSPS] and nonreactive SPS) on the properties of TaB2‐TaC composites was investigated. Ta2O5 and B4C powders were used as starting materials in the RSPS method, and synthesis and densification of TaB2‐TaC composites were accomplished in a facile single step. The effect of sintering temperature and time on the microstructure and densification of the in‐situ RSPS were investigated. The obtained results were compared with nonreactive spark plasma sintered TaB2‐TaC composites. The highest densification (∼99.5%) was achieved for the TaB2‐TaC composite with 6.64 vol.% TaC after reactive sintering at 1550°C under 40 MPa with a 5 min holding time. Although lower SPS temperature was used in the RSPS method, better densification and higher Vickers hardness were obtained compared to the nonreactive SPS. While platelet‐shaped TaC formation was observed in both processes, the average grain size was smaller in the RSPS method. On the other hand, no significant difference was detected in the oxidation behavior of the composites produced by RSPS and nonreactive SPS.

Effect of ageing temperature on the corrosion behaviour of UHTC particulates reinforced magnesium composites fabricated through ultrasonic assisted squeeze casting process

The corrosion behaviour of AZ91D magnesium alloy reinforced with 5-wt% of various Ultra High-Temperature Ceramics (UHTC) such as TaC, HfC, TiN, TiB2, and TiC has been analysed in this current research work. AZ91D magnesium alloy and proposed composites were fabricated through ultrasonic assisted squeeze casting process and followed by T6 heat treatment at different ageing temperatures (170, 200, 230, and 260 °C). As per ASTM standards, the fabricated composites were subjected to various analyses on density, porosity, microstructure, hardness, and corrosion behaviour. The distribution of reinforcements was revealed by the optical microscope and scanning electron microscope images of composites. The presence of primary phase (α-Mg), intermetallic phase (β-Mg17Al12) and reinforcements in the composites were confirmed in the XRD analysis. Because of high densification, lower grain size, and lesser porosity level, TaC and HfC particulate reinforced composites showed higher hardness (170.3 and 160.4 HV respectively) at 230 °C compared to other composites. The salt spray corrosion test (3.5 wt% NaCl) on composites with varying exposure times (24, 48, and 72 h) revealed that, due to the formation of a dense and stable anti-corrosion protective layer with reduced β-Mg17Al12 phase, TaC and HfC composites exhibited higher corrosion resistance up to 48 h and ageing temperature of 230 °C. The scanning electron microscope image of the corroded samples showed pits and crack formation at an exposure period of 72 h.

Preparation and oxidation behavior of Cf/C–TaC composites

Cf/C–TaC composites, which possesses excellent anti-ablation properties, are potential candidate materials for applications in the extreme environments associated with hypersonic flight and rocket propulsion. In this paper, Cf/C–TaC0.89 composites were prepared by chemical vapor infiltration to achieve a TaC matrix with a C/Ta atomic ratio of 0.89. The isothermal oxidation behavior of the composites at 1200–1600 °C was investigated, and the minimum time for the self-healing of microcracks on the composite surface was calculated based on the oxidation process obeying either a parabolic or a linear law. The results indicate that the oxidation process is controlled by surface kinetics in the initial 0–10 min at 1200–1400 °C and 0~5 min at 1500–1600 °C even if a dense oxide layer is formed. After that, the controlling mechanism becomes the diffusion of oxidative gases in a TaCxOy layer, a diffusion barrier layer existed in the oxidation of refractory carbides. The formation of the TaCxOy layer is attributed to the low C/TaC ratio of the TaC0.89 phase and the diffusion behavior of O atoms in Ta octahedral interstitial sites.

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.

Mechanical behaviour of carbon fibre reinforced TaC/SiC and ZrC/SiC composites up to 2100°C

The microstructure and elevated temperature mechanical properties of continuous carbon fibre reinforced ZrC and TaC composites were investigated. Silicon carbide was added to both compositions to aid sintering during hot pressing. Fibres were homogeneously distributed and no fibre degradation was observed at the interface with the ceramic matrix even after testing at 2100 °C. The flexural strength increased from 260 to 300 MPa at room temperature to ∼450 MPa at 1500 °C, which was attributed to stress relaxation. At 1800 °C, the strength decreased to ∼410 MPa for both samples. At 2100 °C plastic deformation resulted in lower strength at the proportional limit (210–320 MPa), but relatively high ultimate strength (370–440 MPa). The sample containing ZrC had a lower ultimate strength, but higher failure strain at 2100 °C due to the weak fibre/matrix interface that resulted in fibre-dominated composite behaviour.

Preparation and characterization of ZrB2 and TaC containing Cf/SiC composites via Polymer-Infiltration-Pyrolysis process

To improve the thermo-chemical resistance of PIP–Cf/SiC composites, the SiC matrix is modified by adding ZrB2 and Ta powder to the pre-ceramic slurry to form Cf/SiC–ZrB2–TaC composites. Within this study the modified composites are investigated regarding their microstructure, chemical composition and physical properties (density=2,39–2,72g/cm3; porosity=20,3–24,8vol.-%; fiber volume content=52–57vol.-%). Mechanical properties are investigated in order to ensure that there is no negative influence by ZrB2 and TaC matrix modification. The matrix modification is followed by an improvement in bending strength (up to 27% increase), Young’s modulus (up to 28% increase) and for interlaminar shear strength (up to 22% increase). Finally the thermo-chemical behavior of the Cf/SiC–ZrB2–TaC composites is evaluated in a combustion chamber-like environment using the Airbus Group long-term material test facility (Environmental Relevant Burner Rig-Kerosene, ERBURIGK). The results show that the thermo-chemical resistance of Cf/SiC–ZrB2–TaC composites is improved and the oxygen permeability through the composite is decreased (from 5 to 1 layer).

Deformation mechanism in graphene nanoplatelet reinforced tantalum carbide using high load in situ indentation

High load in-situ indentation testing with real time SEM imaging was carried out on spark plasma sintered graphene nanoplatelets (GNP) reinforced TaC composites. The prime goal of this study was to understand the deformation behavior and the reinforcing mechanisms of GNPs. The results suggest that addition of GNPs had significant effect on dissipating indentation energy and confining the overall damage area to a localized region of TaC. The average crack length reduced by 26% whereas total damage area shrunk by 85% in TaC-5vol% GNP sample as compared to pure TaC. TEM analysis concluded that well dispersed GNPs result in a strong and clean interface between TaC and GNP with trace amount of amorphous layer that leads to improved energy dissipation mechanism.

Electrochemical Fabrication of Multicore-Shell Ni-TaC Composite Particles in Molten Salt

Ni-TaC composite powder has been synthesized electrochemically from the mixture of NiO, Ta2O5 and carbon in molten CaCl2-NaCl at 800°C. The reaction pathway was investigated by examination of the partially and completely reduced samples recovered from reduction of the NiO/Ta2O5/C pellets in combination with direct extraction of TaC. The results showed that the composite powder with the multicore-shell structure involving the nano-sized TaC particles located inside the micron-sized Ni matrix was formed through the electrochemical route. Ni metal acted as a catalyst to accelerate the reduction of the cathodic pellets by generation and recovery from Ni-Ta alloys. The electrochemical route in molten salt achieved the preparation of TaC and metal-based TaC composites at a relatively lower temperature.

Thermal diffusivity of three-dimensional needled C/SiC–TaC composites

Three-dimensional needled carbon fiber reinforced SiC–TaC composites were prepared by combination of slurry infiltration and reactive melt infiltration. The thermal diffusivity of the composites with different TaC contents was characterized in the temperature range from room temperature to 1400 °C. The results revealed that the temperature dependent thermal diffusivity behavior was independent on TaC content, while the thermal diffusivity values of the composites were influenced by their microstructures. A model based on lattice vibration and microstructure was used to discuss the thermal diffusivity behavior of the C/SiC–TaC composites.

Preparation and properties of 2D C/SiC–ZrB2–TaC composites

Two-dimensional (2D) C/SiC–ZrB2–TaC composites were fabricated by chemical vapor infiltration (CVI) combined with slurry paste (SP) method. 2D laminate was prepared by stacking carbon cloth that was pasted with a mixture of polycarbosilane–ZrB2–TaC slurry. A small amount of carbon fiber tows were introduced into the preform in the vertical direction. After heat-treated at 1800°C, the 2D laminate was densified with SiC by CVI to obtain 2D C/SiC–ZrB2–TaC composites. Properties including flexural strength, interlaminar shear strength, and thermal expansion of the composites were investigated. The ablation test was carried out under an oxyacetylene torch flame. The morphologies of the ablated specimens were analyzed. The results indicate that the adding vertical fiber tows and heat-treatment at 1800°C can greatly improve the mechanical properties of the composites. The co-addition of TaC and ZrB2 powders into C/SiC composite effectively enhance its ablation resistance.

Effects of TaC addition on the ablation resistance of C/SiC

C/SiC–TaC composites were fabricated by powder infiltration (PI) combined with chemical vapor infiltration (CVI) processing. Their ablation resistance performance was evaluated with oxyacetylene torch flame. The ablation morphology and microstructure of the tested samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Energy dispersive X-ray spectrum (EDS), respectively. The results indicated that TaC could improve the ablative resistance of C/SiC composites at ultra high temperatures. Liquid Ta 2O 5 formed due to TaC oxidation could fill the interspaces, cracks, and pores in matrix and to obstruct the diffusing channels of the ablative flames. Presence of TaC and Ta 2O 5 could limit the heat transfer and thus reduce the ablation. The steady SiC–TaC matrix improves the stability of composite.

Processing, mechanical properties and oxidation behavior of TaC and HfC composites containing 15 vol% TaSi2 or MoSi2

Fully dense HfC and TaC-based composites containing 15 vol% TaSi2 or MoSi2 were produced by hot pressing at 1750–1900 °C. TaSi2 enhanced the sinterability of the composites and nearly fully dense materials were obtained at lower temperatures than in the case of MoSi2-containing ones. The TaC-based composites performed better than HfC composites at room temperature, showing values of mechanical strength up to 900 MPa and a fracture toughness of 4.7 MPa·m1/2. However, preliminary oxidation tests carried out in air at 1600 °C revealed that HfC-based composites have a superior high temperature stability compared to TaC-based materials.

Dilatometric behavior and microstructure of sintered Fe–NbC and Fe–TaC composites

Fe-reinforced composites were manufactured by the addition of 10–20 wt.% NbC or TaC particles aiming at improved mechanical and wear behavior. Two varieties of Fe powders from Hoeganaes Corp. were used, Ancorsteel 1000B and 45P. Composites produced using the former variety included a small amount of Fe3P to induce liquid-phase sintering whereas 45P powder was pre-alloyed with P by the manufacturer. The hardness of the matrix was adjusted adding carbon to the composite mixture. The powders were milled for different times and annealed prior to pressing. A dilatometric study was carried out under hydrogen to establish optimum sintering profiles. Relative densities up to 97% TD were achieved. Both microstructure and density of the sintered pellets were evaluated in order to establish correlations involving composition, processing parameters and microstructure of the composite.

Composites ofγ + TaC in the Ni−Ta−C ternary system

The Ni−Ta−C ternary system has been studied at the Ni-rich end of the phase diagram. The investigation was directed toward developing a detailed picture of γ+TaC composites. Alloys were melted with Ta/C atomic ratios of 0.79 to 3.33 in an attempt to define the composition range that would produce two-phase γ+TaC eutectics. The liquidus trough rises in temperature across the ternary diagram moving away from the Ni−C eutectic (1320°C) and toward the Ni−Ni3Ta eutectic (1380°C). Bulk chemistries were determined for aligned regions to map the liquidus trough compositions. Ratios of Ta/C atoms varied from 1.3 to 8.8 in the aligned regions. Matrix composition was determined by electron microprobe analysis, and lattice parameters of extracted TaC fibers were measured by X-ray diffraction. Fiber compositions ranged from TaC0.99 to TaC0.97 as the Ta/C ratio of the aligned region increased. The matrix compositions and TaC stoichiometries were used to map tie-lines across the ternary diagram. Volume fraction and microstructural features of the TaC phase were also studied. The volume fraction of TaC decreased from 6.7 vol pct to 1.7 vol pct as Ta/C increased from 1.3 to 8.8. The decreasing volume fraction can be explained by a lever-arm rule application for the ternary phase diagram, based on the liquidus trough and tie-line compositions determined in this study. The TaC growth axis was in each case, but the carbide morphology changed progressively across the phase diagram. The change in morphology is primarily a consequence of the change in volume fraction. Implications of the findings of this study for more complex γ+MC eutectics will be discussed.