SiC-TiC Composites Research Articles

Spark plasma sinterability of TaC-based composites co-doped with SiC, TiC and graphene

TaC–TiC–SiC composites were successfully fabricated via spark plasma sintering (SPS) method under the conditions of 2000 °C temperature, 8 min dwell time and 35 MPa pressure. The influences of graphene on the microstructure, densification and hardness were studied and the results were compared with those of a graphene-free sample. X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM) were employed to investigate the phase evolution and microstructure, respectively. The XRD analysis detected TaC, TiC and SiC as the main phases, related to the initial raw materials, and some new phases such as Ta 4 C 3 , TaC 0.47 , Ti 5 Si 3 , Ti 3 SiC 2 , Ti 6 C 3.75 , TiSi 2 as well as (Ta,Ti,Si)C solid solution. The presence of such phases implied that many chemical reactions happened during the sintering. Thermodynamic calculations were conducted for each reaction and discussed in details. It was revealed that graphene can promote the densification (~3 %) and hardness (~1.2 GPa) and prevent the grain growth of TiC. Also, the solid solution formation may be facilitated in the presence of graphene.

Integrated high strength and high toughness induced by elongated TiB2 grains in reactive sintered TiB2–TiC–SiC ceramics

AbstractAlthough the addition of other phases into TiB2 matrix to form ceramic composites has been widely used to improve the mechanical properties of monolithic TiB2 ceramics, it is still difficult to greatly enhance the flexural strength and fracture toughness simultaneously. In this work, TiB2–TiC–SiC composites were successfully prepared by reactive spark plasma sintering of Ti3SiC2–B4C–Ti powder mixtures. During the sintering process, TiB2 grains grew into an elongated morphology, endowing the composites with integrated high strength and high toughness. The growth mechanism of TiB2 grains was attributed to the evaporation–condensation kinetics induced by the presence of B2O3. These findings can accelerate the exploration of ceramic composites with excellent comprehensive properties.

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.

Plastic deformation-induced improved mechanical and thermal properties in hot-forged SiC-TiC composite

A novel SiC-20 vol% TiC composite prepared via a two-step sintering technique using 6.5 vol% Y2O3-Sc2O3-MgO exhibited high deformation (60 %) on hot forging attributed to the high-temperature plasticity of TiC (ductile to brittle transition temperature ∼800 °C) and fine-grained microstructure (∼276 nm). The newly developed SiC-TiC composite exhibited a ∼2-fold increase in nominal strain as compared to that of monolithic SiC. The plastic deformation caused by grain-boundary sliding in monolithic SiC was supplemented by the plastic deformation of TiC in the SiC-TiC composite. The hot-forged composite exhibited anisotropy in its microstructure and mechanical and thermal properties due to the preferred alignment of α-SiC platelets formed in situ. The relative density, flexural strength, fracture toughness, and thermal conductivity of the composite increased from 98.4 %, 608 MPa, 5.1 MPa‧m1/2, and 34.6 Wm−1 K−1 in the as-sintered specimen to 99.9 %, 718–777 MPa, 6.9–7.8 MPa‧m1/2, and 54.8–74.7 Wm−1 K−1, respectively, on hot forging.

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.

Dry sliding friction and wear behaviour of TiC-based ceramics and consequent effect of the evolution of grain buckling on wear mechanism

In this study, the dry sliding tribological behaviour of TiC-based ceramics against alumina is elucidated. Monolithic TiC as well as TiC-SiC composites were successfully densified by spark plasma sintering (SPS) using TiC and SiC powders as starting materials. Friction tests were performed using a pin-on-disk-type friction tester wherein alumina was used as counterpart material in an unlubricated condition at room temperature. The friction coefficient for the TiC-based ceramics dry sliding against alumina all initially increased and attained steady state after the first 200 s. The coefficient of friction in the case of monolithic TiC attained steady state earlier than the composites and exhibited the lowest friction coefficient. The specific wear rate of the TiC-based ceramics increased with increasing SiC content; it was lowest when sliding against monolithic TiC. The increase in wear rate in the composites is linked to grain buckling induced fracture owing instability arising from residual compressive stresses inherent in the composite due to mismatch in thermal expansion coefficients between TiC and SiC. The wear mechanism in general appears to be primarily dominated by third-body wear triggered by grain fracture and subsequent grain pull-out.

The effect of TiO2 additive on the electrical resistivity and mechanical properties of pressureless sintered SiC ceramics with Al2O3-Y2O3

In this study, SiC-TiC composite was fabricated by the reaction between TiO2 and SiC and in addition to the effect of TiO2 additive, influence of sintering temperatures on the electrical resistivity, the relationship between electrical resistivity and microstructure, density, indentation fracture resistance and hardness were investigated. The main goal of this study was to improve electrical resistivity while preserving mechanical properties of SiC body. The results showed that with 10 wt% Al2O3-Y2O3, the electrical resistivity reached to 9 × 108 Ω·m. Increasing the amount of TiO2 particles from 2.5 to 10 wt% and changing the sintering temperature from 1850 °C to 1950°C made the electrical resistivity to be variable in the range of 2.2×105 Ω·m to 9 × 108 Ω·m. In this report, the highest density, hardness and indentation fracture resistance for the samples containing 5 wt% additive which were sintered at 1900 °C were 96.2%, 24.4 GPa and 5.8 MPa.m1/2, respectively. Microscopic images showed that if the grain boundary phase is located in the triple points or multiple points of grain boundary, the electrical resistivity will decrease and if it is located in full circumference of the SiC particles, due to failure of conducting pathways through SiC grains, the resistance of ceramics will increase instead.

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 of hot-pressed SiC-TiC composites

SiC-TiC composites, with 0, 5, 10 and 20 vol.% of TiC, were sintered by the hot-pressing technique at temperature of 2000?C under argon atmosphere. SiC sintering process was activated by liquid phase created by the reaction between Al2O3 and Y2O3, in which it is possible to dissolve passivating oxide layers (SiO2 and TiO2) and partially SiC and TiC carbides. Microstructure observation and density measurements confirmed that the composites were dense with uniformly distributed components. Differences in thermal expansion coefficients between SiC and TiC led to complex stress state occurrence. These stresses combined with the liquid-derived separate phase between grains boundaries increased fracture toughness of the composites, which ranged from 5.8 to 6.3MPa?m0.5. Opposite to the bending strength, fracture toughness increased with the TiC volume fraction. By means of simulation of residual thermal stresses in the composites, it was found that with the increasing volume fraction of TiC, tensile stress in TiC grains is reduced simultaneously with strong rise of compressive stresses in the matrix.

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.

A novel approach for preparation of dense TiC–SiC nanocomposites by sol–gel infiltration and spark plasma sintering

Abstract Dense TiC–SiC nanocomposite ceramics were prepared by infiltration of porous TiC scaffolds with a Si O C sol, followed by spark plasma sintering (SPS). The porous nano TiC scaffold was first synthesized by direct carbothermal reduction of a monolithic Ti O C precursor obtained from a controlled sol–gel process. The TiC scaffold was infiltrated with a Si O C sol and then the sample was aged in a container for 48 h at 80 °C to convert the sol into gel. After this, the sample was heated at 550 °C to remove the organic components and then 1350 °C to convert the Si O C gel to SiC by carbothermal reduction reaction. The cycle of the infiltration and carbothermal reduction was repeated several times to obtain relatively dense TiC–SiC composite samples. Dense TiC–SiC composite with a uniform nano-sized grain microstructure was obtained by spark plasma sintering at 1800 °C for 5 min under 40 MPa uniaxial pressure. Compared with conventional powder mixing methods, the sol–gel infiltration approach has shown distinct advantages of achieving dense TiC–SiC composites with uniform nano-sized grain structures.

Spark plasma sintering of TiC-based composites toughened by submicron SiC particles

Abstract TiC-based composites toughened by submicron SiC particles with improved fracture toughness were fabricated and fracture mechanism has been investigated. It has been found that the improvement in fracture toughness of TiC–SiC composites is due to both crack paths propagating through uniformly distributed SiC particles and the fracture mode transition from intergranular type to transgranular type caused by the change of residual stresses originating from the addition of SiC particles. The optimum of fracture toughness (5.2 MPa m 1/2 ) was achieved at 14.6 vol% SiC, whereas the toughness decreased with increasing amount of SiC beyond 30 vol%.

Fabrication and characterization of sintered TiC–SiC composites

Some TiC–SiC composites with different SiC volume contents (0, 10, 25 and 50%) are prepared by spark plasma sintering (SPS). The relationship between density, grain growth and temperature is studied in order to fabricate dense and nano-sized TiC–SiC composites. A sintering by SPS at 1800 °C during 5 min allowed to form TiC–SiC composites with relative density above 95% and an homogeneous distribution of TiC (grain size from 270 to 900 μm) and nano-sized SiC. With the increasing of SiC volume contents, Vickers hardness and fracture toughness are improved; thermal conductivity at room temperature is increased whereas at high temperature it is reduced. In future studies, those materials will be irradiated to characterize monolithic TiC and TiC–SiC composites behaviour under irradiation.

Fabrication and tribological characterization of gradient carbon layer derived from SiC-TiC composites

Fabrication and tribological characterization of gradient carbon layer derived from SiC-TiC composites

Characterization of sintered TiC–SiC composites

TiC–SiC composites were fabricated using TiC and SiC powders as starting materials at the range of 1650–2000 °C in Ar atmosphere by two-step method. In the first step, the ingots with intragranular SiC or TiC particle were prepared by arc-melting technique, subsequently, crushed and ground into TiC and SiC composite powders. In the second step, TiC–SiC composites were sintered using these as-prepared composite powders by SPS method. It was concluded that these TiC–SiC composites prepared by two-step method showed more excellent properties than that prepared by arc-melting technique. The hardness of the fabricated TiC–SiC composites was 25–27 GPa at the load of 0.98–9.8 N, which was obviously greater than that of arc-melting composites. The thermal conductivity of the TiC–SiC composites was 18–48 W K −1 m −1 at the range of 298–1273 K and slightly decreased with increasing temperature. The electrical conductivity of the composites was (2–5) × 10 5 S m −1 at the range of 298–1273 K and slightly decreased with increasing temperature.

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.

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.

Fracture Toughness Enhancements through Stress Shielding in Functionally Graded SiC-TiC Composites

It is often the case that the low fracture toughness of polycrystalline ceramics limit the load-bearing capabilities of components made from such materials. In an effort to improve the fracture toughness of a SiC-TiC composite material, a novel stress-shielding approach was adopted so as to reduce the effective mode I stress intensity around a crack tip within the composite body. To this end, a series of functionally graded materials were produced, with samples having a preselected spatial SiC-TiC composition variation. The spatial composition variation within each sample was set up according to one of several exponential mathematical functions. In this way the resultant spatial variation in thermal expansion coefficients was also controlled through the thickness of the material, and a particular stress and strain distribution could be tailored within the body. Samples with tailored near-surface compressive stress states showed a significant improvement in c KI , as measured by means of a flexure test, in comparison with stress-free samples of a homogeneous composition corresponding to the composition found at the test-point within the gradient materials.

Microstructure and Mechanical Properties of Spark-Plasma-Sintered SiC-TiC Composites

Rapid densification of the SiC-10, 20, 30, 40wt% TiC powder with Al, B and C additives was carried out by spark plasma sintering (SPS). In the present SPS process, the heating rate and applied pressure were kept at 100°C/min and at 40 MPa, while the sintering temperature varied from 1600-1800°C in an argon atmosphere. The full density of SiC-TiC composites was achieved at a temperature above 1800°C by spark plasma sintering. The 3C phase of SiC in the composites was transformed to 6H and 4H by increasing the process temperature and the TiC content. By tailoring the microstructure of the spark-plasma-sintered SiC-TiC composites, their toughness could be maintained without a notable reduction in strength. The strength of 720 MPa and the fracture toughness of 6.3 MPa·m1/2 were obtained in the SiC-40wt% TiC composite prepared at 1800°C for 20 min.