SiC TiC Research Articles

Microstructure and EMW absorption properties of PDCs-SiCN(Ti) ceramics with adjustable SiC nanowires and TiC nanocrystallines

Herein, a novel type of ceramic material exhibiting tunable electromagnetic properties was synthesized using the polymer-derived ceramics (PDCs) method. The precursor employed in this process was a tetrabutyl titanate-modified polysilazane, which ultimately led to the formation of PDCs-SiCN(Ti) ceramics. High-temperature annealing (1400 °C-1500 °C) was used to prepare PDCs-SiCN(Ti) ceramics, which exhibited a unique dual nanostructure comprising SiC nanowires and TiC nanocrystals and served as effective nanoabsorbents. The SiC and TiC contents are closely related to the annealing temperature and induced Ti content. After annealing at 1500 °C, the PDCs-SiCN(Ti) ceramics with the typical A + B + C electromagnetic absorbing structure exhibited excellent electromagnetic wave (EMW) absorption properties. The PDCs-SiCN(Ti) ceramics, with a Ti content of 5 wt%, demonstrated an effective absorption bandwidth (EAB) of 3.8 GHz, which encompassed 90.5 % of the X band, despite having a relatively thin impedance matching thickness of only 2.1 mm. The outstanding EMW attenuation capability of the PDC-SiCN(Ti) ceramics can be ascribed to their large specific surface area and defects combined with the high permittivity of dispersed TiC nanocrystals, which facilitates multiple reflections of EMW within the SiCN matrix. Therefore, this work provides a controllable preparation method for PDCs-SiCN(Ti) ceramics with various microwave absorbing phases.

Synthesis and formation mechanism of ZrC–SiC–TiC ceramic powders with high-sinterability via sol-gel process and carbothermal reduction

In this work, high-sinterability ZrC–SiC–TiC ceramic powders were synthesised through a sol-gel approach coupled with subsequent carbothermal reactions. Specifically, MgCl2 was utilised as an additive to enhance the sintering activity of the powders. Experimental results revealed that the introduction of Mg and variation in Zr/Ti molar ratios significantly influenced the phase and morphological evolution of the precursor. In the form of a Mg–Si–O liquid phase, Mg promoted carbothermal reduction and solid-solution reactions. It ultimately remained as amorphous Mg–Si–O oxide in the final ZrC–SiC–TiC ceramic powders, effectively improving the sintering activity of ceramic powders. Consequently, dense Mg-modified ZrC–SiC–TiC ceramics with high relative density up to 99.2 % were successfully fabricated by spark plasma sintering at 1700 °C and 30 MPa.

Influence of TiC addition on ablation and thermal shock behaviour of microwave sintered ZrB2–SiC–TiC composites

Ultra-high temperature ceramics should possess excellent ablation and thermal shock resistance in order to endure severe temperatures for ultra-high temperature space applications. The study reports the effect of TiC (5–10 vol. %) addition on ablation and thermal shock resistance of microwave sintered ZrB2-25 SiC (vol. %) composites. The ablation and thermal shock resistance improved with TiC addition due to the formation of TiO2 and ZrO2.TiO2 layers on the surface of oxidized composites. The composites retained up to 91.95% of maximum hardness and 91.61% of maximum fracture toughness after ablation. Crack deflection and crack bridging were observed as the primary toughening mechanisms after ablation. The thermal shock resistance also improved with TiC addition. The analytically estimated thermal shock parameters as well as the experimentally measured critical temperature difference increased with TiC addition. The enhancement in thermal shock resistance was ascribed to the higher flexural strength and fracture toughness of developed composites.

Effect of TiC addition on structure and properties of spark plasma sintered ZrB2–SiC–TiC ultrahigh temperature ceramic composite

In this study, the role of 5 and 10 vol% TiC addition on densification, microstructure, phase evolution and mechanical properties of ZrB2–20 vol% SiC composite has been investigated maintaining the volume fraction of SiC constant. It is found that TiC addition reduces the spark plasma sintering (SPS) temperature from 1900°C to 1700°C producing in a nearly fully dense (∼99.6% theoretical density) material and forming (Zr,Ti)B2, a mixed compound of Zr and Ti. The lattice parameters (c and a) of (Zr,Ti)B2 are found to lie between that of pure ZrB2 and TiB2 with its c/a ratio varying inversely with the extent of TiC addition. Phase and microstructure analyses reveal that, while the entire amount of TiC dissolves in ZrB2 in the ZrB2–20SiC–5TiC (vol%), undissolved TiC exist in the ZrB2–20SiC–10TiC (vol%) composite after sintering indicating that the solubility limit of TiC in sintered ZrB2 lies in between 5 and 10 vol%. The elastic modulus values of the TiC added composites predicted by model based calculation agree well with the values experimentally determined by nano-indentation suggesting that these sintered composites are highly dense and nearly defect-free. The calculated residual stress of the matrix phase (using appropriate analytical models) was found to be tensile in nature but decreasing with increase in TiC addition. The residual stress of the reinforcement phase manifests similar trend but is compressive in nature. Compared to the conventional ZrB2–20SiC (vol%) composite, TiC added composites record better bulk and nano-mechanical properties (e.g., hardness, indentation fracture toughness, flexural strength, stiffness and elastic modulus) at ambient temperature indicating that the ZrB2–SiC–TiC system is a more promising ultrahigh temperature ceramics than the base composite.

Effect of TiC incorporation on the optical properties and oxidation resistance of SiC ceramics

In concentrating solar power (CSP) technologies, the absorber material should be spectrally selective under severe operating conditions, i.e., ~1000 °C under air atmosphere. SiC–TiC nanocomposites could be good candidates for this application due to their spectral selectivity at room temperature; however, their behaviour under CSP operating conditions is unknown. Therefore, the spectral selectivity and oxidation resistance of TiC–SiC composites were studied up to 500 °C, in air, and at various compositions. During heating, the emittance increased with the temperature. After heating, the TiC grains at the surface were oxidized to TiO2, while SiC grains showed good behaviour. However, despite little oxidation, the spectral selectivity of the nanocomposites remained interesting after heating. Specific oxidation tests of up to 9 days at 1000 °C in air showed an increase in the oxidation resistance with the amount of SiC. This result is the consequence of the formation of a protective layer of SiO2 that prevents oxidation of the TiC grains. The composition of 30 at% TiC–70 at% SiC is a good compromise between low oxidation and good selectivity.

Sol–Gel Synthesis of Functionally Graded SiC–TiC Ceramic Material

Functionally graded SiC–TiC composite materials are promising for using in the aerospace industry as relatively low-density materials. The production of such materials by the sol–gel synthesis of a finely divided titanium carbide matrix in the pore space of SiC frameworks was studied. It was demonstrated that the distribution of the TiC matrix in the space of the SiC framework can be changed by varying the composition of the coordination sphere of precursors. It was shown that, after eight cycles of hydrolysis of titanium-containing precursors in the presence of a phenol formaldehyde resin with subsequent carbonization and carbothermal synthesis (1400°C, dynamic vacuum, 2 h), the weight gains of the samples differed significantly: for the precursor [Ti(OC4H9)2.05(O2C5H7)1.95], which is more sensitive to moisture, it was 23%, and for the complex [Ti(OC4H9)1.95(O2C5H7)2.05], it was 37%. Moreover, in the former case, near-surface regions of the material were predominantly densified. It was noted that, with increasing content of the modifying phase TiC, the compressive strength increased, and the specific surface area decreased (as determined by low-temperature nitrogen sorption and mercury porosimetry). The obtained gradient of the composition of the SiC–TiC ceramics across the depth was confirmed by X-ray computed microtomography: the total porosity of the near-surface regions of the ceramics differed by a factor of 2.9.

Fabrication of Ti3SiC2/SiCp multiport minichannel plates for high-temperature applications

An innovative method for fabricating ceramic multiport minichannel plates (MMP) has been developed. The essence of the method is the combustion synthesis of Ti3SiC2/SiCp ceramic matrix composite using sandwich assembly of titanium metal items, viz. rods and sheets, and tape-cast rubber films filled with SiC particles and TiC additive. The fabrication route consists of hot pressing of starting materials at 100 °C under 60 MPa in air into a single integrated unit followed by heat treatment at 1400 °C in a vacuum hot press furnace under small uniaxial load of 80 N. It is shown that the one-dimensional titanium metal items act as both reactants and channel-forming templates. The MMP prepared by the proposed method contains primarily of 45 vol.% Ti3SiC2 and 44 vol.% SiC, as well 11 vol.% TiSi2 minor component. The material exhibits a composite microstructure consisting of a dense Ti3SiC2-based matrix and SiC particles uniformly embedded in it. The sample contains parallel-aligned hollow cylindrical channels of 0.8 mm in diameter distributed with a center-to-center spacing of 1.3 mm. The volume fracture of the channels is estimated to be about 19%.

Cutting performance and crack self-healing mechanism of a novel ceramic cutting tool in dry and high-speed machining of Inconel 718

The cutting performance of self-developed novel Al2O3-based ceramic tool (Al2O3/SiCw/TiCn) reinforced by SiC whisker and TiC nanoparticle was investigated experimentally in dry and high-speed machining of Inconel 718. Combining with the high-temperature mechanical properties and microstructure evolution of the tool material, the failure mechanism of the novel ceramic tool was revealed. The results showed that the novel ceramic tool can be used stably in dry machining of Inconel 718 at a high speed of 400 m/min. The service life of novel ceramic tool was 50% higher than that of the commercial Al2O3-based ceramic tool CC670 toughened by SiC whisker. The novel ceramic tool did not suffer from fracture failure and exhibited good resistance to flank wear and notch wear. For the tool failure mechanism, it shows that TiC nanoparticle improved the high-temperature hardness and high-temperature fracture toughness of tool materials, which was an important reason for the better wear resistance of novel ceramic tool. In the service conditions of dry and high-speed machining, the cutting temperature was as high as 1200 °C at which the SiC whisker was oxidized to form glassy phase. The crack of the tool was self-healed and the crack tip was passivated by glassy phase, which suppressed crack propagation to prevent fracture of the ceramic tool.

SiC-TiC nanocomposite for bulk solar absorbers applications: Effect of density and surface roughness on the optical properties

In this study, the potential of SiC-TiC nano-composites as solar absorbers has been studied. For solar thermal applications, materials with high solar absorptance and low emittance are ideally sought for (spectral selectivity). A semi-molecular sol-gel synthesis route leading to nanometric homogenous composites was described. The resulting SiC-TiC nanocomposite powder was sintered at different temperatures to produce samples with various relative densities (from 57% to 96%). The samples morphology and composition were characterized by several techniques including Scanning Electron Microscopy (SEM), Energy-Dispersive X-Ray Spectroscopy (EDX), X-Ray Diffraction (XRD), carbon and oxygen elemental analyses. The link between the surface roughness and the relative density was precised and the effects on the optical properties (0.25–25 µm wavelength range) were studied. Comparisons were made with pure SiC and pure TiC samples with various relative densities.Overall, the sample emittance was found to strongly decrease with the increase in the relative density, leading to a great increase in the spectral selectivity, despite a little decrease in the solar absorptance. The TiC-SiC composite has an intermediate reflectance compared to the pure SiC and the pure TiC samples. With an absorptance of 0.76, an emittance of 0.44 and a selectivity of 1.74, the denser SiC-TiC could be a good candidate for bulk solar applications.

Mechanical properties of reaction sintered SiC-TiC composite

SiC-TiC composite containing 5–30 vol% TiC particles was fabricated by conversion of TiO2 to TiC during pressureless sintering. The presence of very fine and uniformly distributed, in-situ created TiC particles increased driving force for sintering allowing fabrication of high density SiC-TiC composite without the use of external pressure. The highest mechanical properties were measured in samples sintered at 1885 °C for 1 h. The highest values for hardness (~ 20 GPa) and fracture strength (~ 490 MPa) were measured in samples containing 5 vol% TiC, whereas the highest fracture toughness (~ 5.5 MPa ⋅m1/2) was measured in samples containing 10 vol% TiC. The presence of in-situ created, uniformly distributed TiC particles was beneficial for activation of not only the crack deflection mechanism but also mechanism called toughening by residual stress crated due to the difference of thermal expansion between SiC matrix and TiC particles. The compressive stress field around TiC particles acts to close the propagating crack and thus to increase fracture toughness.

Mechanical properties and microstructure characterization of spark plasma and conventional sintering of Al–SiC–TiC composites

This work presents fabrication and characterization of Al–SiC–TiC composite materials containing 15 wt% SiC and 5 wt% TiC as reinforcing phases. The spark plasma and conventional sintering were done at 440 °C for 25 min and 600 °C for 60 min, respectively. The results indicate that the mechanical properties obtained by sprak plasma process are much higher than conventional sintering. The 99.2 ± 0.4% and 90.4 ± 0.7% of theoretical density were measured for samples sintered by SPS and conventionally, respectively. XRD analyses indicate no decomposition of SiC and TiC reinforcements. SEM investigations demonstrate uniform distribution of reinforcement particles in aluminum matrix and also fine microstructure of the SPS samples.

Fabrication of diamond–SiC–TiC composite by a spark plasma sintering-reactive synthesis method

Abstract Diamond–SiC–TiC composites were fabricated by a spark plasma sintering method which reduced the chance of graphitization of diamond due to its short sintering time. Ti and Si powder were used to consume the graphite occurred in the sintering process which reacted with C generating SiC and TiC chemically bonded diamond composites. The results suggested that no graphite phase presented in the composites sintered at 1200–1650 °C. Both bending strengths and relative densities of the composites increased along with the sintering temperature, and achieved up to 829 MPa and 99%, respectively, when the composites were sintered at 1650 °C for 10 min. Graphite emerged as a separate phase in the composites which were sintered at 1700 °C for 10 min, leading to the rapid decrease of the bending strengths and the relative densities.

Nanoscale multilayered and porous carbide interphases prepared by pressure-pulsed reactive chemical vapor deposition for ceramic matrix composites

In Ceramic Matrix Composites (CMCs) reinforced by continuous fibers, a good toughness is achieved by adding a thin film called “interphase” between the fiber and the brittle matrix, which acts as a mechanical fuse by deflecting the matrix cracks. Pyrocarbon (PyC), with or without carbide sub-layers, is typically the material of choice to fulfill this role. The aim of this work was to study PyC-free nanoscale multilayered carbide coatings as interphases for CMCs.Nanoscale multilayered (SiC–TiC)n interphases were deposited by pressure-Pulsed Chemical Vapor Deposition (P-CVD) on single filament Hi-Nicalon fibers and embedded in a SiC matrix sheath. The thicknesses of the carbide interphase sub-layers could be made as low as a few nanometers as evidenced by scanning and transmission electron microscopy. By using the P-ReactiveCVD method (P-RCVD), in which the TiC growth involves consumption of SiC, it was not only possible to obtain multilayered (SiC–TiC)n films but also TiC films with a porous multilayered microstructure as a result of the Kirkendall effect. The porosity in the TiC sequences was found to be enhanced when some PyC was added to SiC prior to total RCVD consumption. Because the porosity volume fraction was still not high enough, the role of mechanical fuse of the interphases could not be evidenced from the tensile curves, which remained fully linear even when chemical attack of the fiber surface was avoided.

Microstructure and hardness of SiC–TiC nanocomposite thin films prepared by radiofrequency magnetron sputtering

Silicon carbide–titanium carbide (SiC–TiC) nanocomposite thin films were prepared by radiofrequency magnetron sputtering using SiC–TiC composite targets fabricated by spark plasma sintering. The SiC thin films were amorphous at substrate temperatures below 573K and crystallized in the cubic crystal system (3C) at substrate temperatures greater than 773K. Cubic SiC–TiC nanocomposite thin films, which contain a mixture of 3C-SiC and B1-TiC phases, were obtained at a TiC content of greater than 20mol%. The amorphous films possessed a dense cross-section and a smooth surface. The morphology of the SiC–TiC nanocomposite thin films changed from granular to columnar with increasing substrate temperature. The SiC–TiC nanocomposite thin films prepared at TiC content of 70–80mol% and substrate temperature of 573K showed the highest hardness of 35GPa.

Joining of carbon/carbon composites for nuclear applications

Using hot pressing, carbon/carbon composites were joined using a Ti3SiC2/SiC interlayer which was in situ synthesized by the reaction of TiC and Si. Phase composition of the interlayer was characterized by X-ray diffraction. Morphologies of the joints before and after shear test were determined by scanning electron microscope and energy dispersive spectroscopy. The mechanical strength of the joints was assessed by shear strength test. Phase analysis reveals that the interlayer was mainly composed of ternary Ti3SiC2, SiC, and little TiC. The microstructure observation results show that the dense and uniform interlayer adheres firmly to the C/C composites. A composition gradient reaction layer was formed at the joining interface between C/C substrates and interlayer. The room temperature average shear strength of the joints is about 38.9 ± 3.6 MPa. The joining mechanism and failure behavior of the joints were also discussed.

Reaction of TiC with SiCl 4 vapor with formation of SiC–TiC composites

The reaction of TiC grains with SiCl 4 vapor was carried out in Ar at 1000–1600 °C to produce TiC–SiC composite powders. The compositions of these powders were controlled by controlling the conversion to SiC, which depends on the reaction temperature. The phases formed by the solid–gas reaction were identified by X-ray analysis (XRD) and the molar ratio of SiC to TiC in the powder was estimated from the area ratios of the respective XRD peaks. The reaction begins at about 1100 °C and its rate increases with temperature to 1600 °C, at which 92% SiC is formed. The morphology of the TiC–SiC composites was observed by scanning electron microscopy and transmission electron microscopy and a reaction mechanism is deduced from the above results and thermodynamic considerations. TiC–SiC composites were densified by spark plasma sintering at 1750 °C and 40 MPa to the relative density 92–96% and a Vickers hardness of 1700–1900 Hv.

An analysis of thermal residual stresses in SiC f/Cu composites when TiC or Ni as binder

The interfacial bonding strength of SiC fiber reinforced copper matrix composites is extremely weak. Using Ti or other metallic elements such as Fe, Ni, Mo can improve the fiber/matrix bonding strength because these elements can form carbides or an interdiffusion zone between the fiber and the matrix though a heat treatment. In this paper, a TiC reaction layer or Ni interlayer is introduced as a binder, and thermal residual stresses (TRS) in the SiC fiber, TiC or Ni interlayers, and matrix are simulated by means of finite element method. The results indicate that the matrix undergoes significant plastic deformation when the composite is cooled to room temperature from the bonding temperature, and the residual plastic strains are highest around the interlayers and decrease as distance from the interlayer increases; the values and distributions of hoop stresses and Von Mises stresses in the matrix are nearly identical when different interlayers are used , while the magnitudes of these stresses are significantly different in different kinds of interlayers. The distribution characteristics of axial residual stresses in the matrix change when different interlayers are used, and Ni is superior to TiC as the axial stresses greatly decrease near the axial end of the composite.

The synthesis of SiC and TiC protective coatings for carbon fibers by the reactive replica process

The possibility to use the reactive replica technique to synthesize mono- and multi-layer coatings make it possible to cover carbon materials of complex shape by a ceramic layer. The reactive replica synthesis requires two steps: the deposition of an oxide layer on the carbon material by a sol–gel process, and a heat treatment above 1400 °C to form the carbide by reaction between the carbon material and the oxide layer. Several multi-layer coatings based on SiC and on SiC–TiC were synthesized by this process by using different carbon fibers. In this study, mono- and multi-layer carbide coatings were prepared on four different carbon fibers by the reactive replica technique to improve their resistance to oxidation between 500 and 1000 °C. The characteristics (surface area, thickness, …) of the carbide layers were studied in relation to the synthesis parameters such as the carbon surface properties, the nature of the carbide and the oxide thickness. The resistance to oxidation of the ceramic layers which can act as protective layers was studied between 500 and 1000 °C. The oxidation kinetics of the pristine and coated carbon fibers were studied in isothermal conditions by thermogravimetric analysis. It was observed that the surface of the pristine carbon fiber has a great influence on the efficiency of the protective coating. The thermogravimetric study showed that below 800 °C, the oxidation is controlled by the rate constant of the reaction either for non-coated or coated carbon fibers. Above this temperature, the oxidation rate is limited by the diffusion of oxygen through the coating layer. Moreover, the activation energy of the kinetic constant of the oxidation is not changed by the addition of the protective layer. This behaviour is an indication that the ceramic layer does not act as a diffusion barrier, the protection efficiency may be more related to the fact that the ceramic formation proceeds on the active sites of the carbon fibers, and therefore reduces its reactivity toward oxygen. The most effective protection against oxidation was obtained with a double layer of SiC. The addition of TiC in the protective layer either as a multi-layer of SiC and TiC or as a mono-layer of a mixture of the two carbides does not lead to any improvement of the protection efficiency against carbon oxidation.

Microstructure, Phase and Thermoelastic Properties of Laminated Liquid‐Phase‐Sintered Silicon Carbide–Titanium Carbide Ceramic Composites

Hot‐pressed silicon carbide–titanium carbide (SiC—TiC) composites sintered with liquid‐phase forming Al2O3 and Y2O3 mixtures have been studied. Samples were fabricated by successively stacking tape‐cast sheets of a single composition, resulting in a laminated body of uniform composition. This approach required the development of a technology easily transferable into the production of functionally graded SiC–TiC materials. The effects of this processing route on the resultant microstructures and phases were explored in detail. Additionally, because of the consequences for graded materials, the effects of TiC proportion on the thermal expansion coefficients, Young's modulus, and Poisson's ratios for several SiC–TiC composites were also determined.

しごき加工におけるDLC被膜損傷に及ぼす接触界面への硬質粒子かみ込みの影響

A series of experiments was carried out to investigate the influence of hard particles on diamond-like carbon (DLC) coating damage in the strip-ironing process. Three types of commercially available DLC coating were used as die coatings on alloy tool steel SKD11 substrates. Three types of hard particles, namely, sand, SiC and Al2O3, were used. Experiments under dry conditions showed no DLC coating damage after ironing with a dull-finished sheet, but DLC coating damage can be observed at the interface inlet when using a sheet finished with abrasive paper. In the case of aluminum sheet (A1050-H24), severe galling is observed under dry conditions. When using a lubricant with hard particles, no DLC coating damage can be observed in samples with sand or Al2O3 particles, but severe DLC coating damage can be observed in samples with SiC particles. The degree of DLC coating damage becomes greater with a high-tensile-strength steel sheet than with an aluminum sheet. The TiN coating is also destroyed by SiC particles but TiC coating damage is negligible.