Synthesis,microstructure, and mechanical properties of TiC-SiC-Ti3SiC2 composites prepared by in situ reactive hot pressing

In this work, TiC-SiC-Ti₃SiC₂ composites were synthesized by in situ reactive hot pressing using β-SiC, graphite, and TiH₂ powders as initial materials. Microstructure and mechanical properties of as-prepared dense composites were systematically investigated. It was found that by increasing the initial SiC content the final SiC content in the composites increased in contrast to the decrease in TiC and Ti₃SiC₂ contents. In the dense composites, TiC and Ti₃SiC₂ grains exhibited transgranular fracture, whereas SiC particles showed intergranular fracture. The composite containing 77 vol.% TiC, 4 vol.% SiC, and 19 vol.% Ti₃SiC₂ had the highest flexural strength of 706.6 MPa. The composite consisting of 44 vol.% TiC, 49 vol.% SiC, and 7 vol.% Ti₃SiC₂ exhibited the highest Vickers hardness of 22.3 GPa and the highest fracture toughness of 6.0 MPa·m^1/2.     

Improved mechanical properties of reaction-bonded SiC through in-situ formation of Ti3SiC2

Reaction-bonded SiC is a ceramic with excellent thermal properties, good corrosion resistance and the characteristic of near-net-shape manufacturing. However, the poor fracture toughness of free Si limits the applications of reaction-bonded SiC. In this study, TiC was added to reaction-bonded SiC and reacted with free Si to form Ti₃SiC₂. The effects of TiC and carbon black on the mechanical properties of reaction-bonded SiC were investigated. The results demonstrated that the in-situ formation of Ti₃SiC₂ and decrease in the content and size of free Si improved the mechanical properties of reaction-bonded SiC ceramics. The mechanical properties of TiC-added reaction-bonded SiC with 17.5 wt% carbon black were superior to those of TiC-added reaction-bonded SiC with 15 wt% carbon black. Moreover, increasing the TiC content of reaction-bonded SiC with 17.5 wt% carbon black from 0 to 7.5 wt% caused an increase in its bending strength from 183.92 to 424.43 MPa and an increase in fracture toughness from 3.7 to 5.24 MPa m^1/2.     

Effect of excess silicon content on the formation of nano-layered Ti3SiC2 ceramic via infiltration of TiC preforms

The aim of this work was to investigate the effect of silicon content on the formation and morphology of Ti₃SiC₂ based composite via infiltration of porous TiC preforms. The gelcasting process was used for fabrication of preforms. It was found that the infiltrated sample at 1500 °C for 90 min from a mixture of 3TiC/1.5Si containing 92 wt.% Ti₃SiC₂. With the increasing of TiC and SiC impurity phases, Vickers hardness was increased to the maximum value of 12.9 GPa in Ti₃SiC₂–39 wt.%TiC composite. Microscopic observations showed that the Ti₃SiC₂ matrix was composed of columnar, platelike and equiaxial grains with respect to silicon content.     

Phase analysis and wear behavior of in-situ spark plasma sintered Ti3SiC2

In-situ synthesis of dense near-single phase Ti₃SiC₂ ceramics from 3Ti/SiC/C/0.15Al starting powder using spark plasma sintering (SPS) at 1250 °C is reported. Systematic analysis of the phase development over a range of sintering temperatures (1050–1450 °C) suggested that solid state reactions between intermediate TiC and Ti₅Si₃ phases lead to the formations of Ti₃SiC₂. The effect of starting powder composition on phase development after SPS at 1150 °C was also investigated using three distinct compositions (3Ti/SiC/C, 2Ti/SiC/TiC, and Ti/Si/2TiC). The results indicate that the starting powder compositions, with higher amounts of intermediate phase such as TiC, favor the formation of Ti₃SiC₂ at relatively lower sintering temperature. Detailed analysis of wear behavior indicated that samples with higher percentage of TiC, present either as an intermediate phase or a product of Ti₃SiC₂ decomposition, exhibited higher microhardness and better wear resistance compared to near single phase Ti₃SiC₂.     

Joining of SiCf/SiC using a layered Ti3SiC2-SiCw and TiC gradient filler

A layered filler consisting of Ti₃SiC₂-SiC whiskers and TiC transition layer was used to join SiC_f/SiC. The effects of SiC_w reinforcement in Ti₃SiC₂ filler were examined after joining at 1400 or 1500 °C in terms of the microstructural evolution, joining strength, and oxidation/chemical resistances. The TiC transition layer formed by an in-situ reaction of Ti coating resulted in a decrease in thermal expansion mismatch between SiC_f/SiC and Ti₃SiC₂, revealing a sound joint without cracks formation. However, SiC_f/SiC joint without TiC layer showed formation of cracks and low joining strength. The incorporation of SiC_w in Ti₃SiC₂ filler showed an increase in joining strength, oxidation, and chemical etching resistance due to the strengthening effect. The Ti₃SiC₂ filler containing 10 wt.% SiC_w along with the formation of TiC was the optimal condition for joining of SiC_f/SiC at 1400 °C, showing the highest joining strength of 198 MPa as well as improved oxidation and chemical resistance.     

Improving hardness and toughness of plasma sprayed Ti–Si–C nano-composite coatings by post Ar-annealing

Ti–Si–C (TSC) composite coatings were fabricated by plasma spraying using Ti/Si/graphite agglomerates as feedstock. Ar-annealing was carried out to reduce the intrinsic defects and increase the performance of the as-sprayed TSC coating. The effects of the annealing temperature (500–900 °C) on the microstructures and mechanical performances of the TSC coatings were investigated. All TSC coatings consisted of TiC, Ti₅Si₃ and MAX phase Ti₃SiC₂. With the increase in temperature (>700 °C), TiC became predominant, while the Ti₃SiC₂ phase content increased, which was accompanied by a decrease in Ti₅Si₃ content. The high -temperature annealing (>700 °C) led to a homogenous microstructure with a relatively low porosity and increased number of micro-cracks. Notably, the hardness and fracture toughness of the TSC coating were simultaneously increased after the annealing, from 1164 HV to 1.96 MPa m^1/2 to 1560 HV and 3.45 MPa m^1/2, respectively. The formation of nanoscale TiC and Ti₅Si₃ with a network distribution, uniform and dense microstructure, and toughening effects of Ti₃SiC₂ and micro-cracks provided the high mechanical performances of the TSC composite coatings.     

Improving thermal stability of SiC whiskers via nanoscale Ti3SiC2 coatings

Effects of SiC whiskers (SiC_w) on the mechanical properties of composites largely depend on their thermal stability at high temperature. In this study, pure SiC_w and Ti₃SiC₂ coated SiC_w were thermal treated at 1600–1800°C for 1 h. Their phase assemblage, morphology, and structural evolution were investigated. Oxygen partial pressures in the graphite furnace resulted in the breakdown of SiC_w into particles at 1600°C, and the degradation became more pronounced with temperature increasing. The thermal stability of SiC whiskers at 1600–1700°C was significantly improved by a thin Ti₃SiC₂ coating on them, as both thermodynamic calculations and experimental observations suggest Ti₃SiC₂ coating could be preferentially oxidized/decomposed, prior to the active oxidation of SiC. At 1800°C, the protective role of the coating on the whiskers became weakened. SiC was converted into gaseous SiO and CO, with the remaining of interconnected TiC micro-rods and amorphous carbon.     

Microstructure and mechanical properties of in situ produced Ti5Si3/TiC nanocomposites

The microstructure and mechanical properties of in situ produced Ti₅Si₃/TiC nanocomposites have been studied. Ti₅Si₃/TiC composites have been prepared by reaction hot pressing mixed powders of elemental Ti, Si and SiC. XRD, SEM, TEM were employed to characterize the structure of the composites. When no elemental Si is added, the resulting composite contains 65 vol.% Ti₅Si₃, with a small amount of carbon dissolved in it. The majority of the TiC particles are nanosized. A small fraction Ti₃SiC₂ grains, with an average size 100 nm, are located in the TiC particles while other elongated Ti₃SiC₂ grains in the Ti₅Si₃ matrix. The highest bending strength of the Ti₅Si₃/TiC composites is 510 MPa at room temperature, which is approximately 6 times that of the monolithic Ti₅Si₃ material. The fracture toughness of the composites exceeds that of pure Ti₅Si₃, and at 1100°C, the yield strength of Ti₅Si₃/35TiC reaches 800 MPa.     

Carbon atmosphere effect on Ti3SiC2 based composites made from TiC/Si powders

The effect of carbon activity and CO pressure in the furnace atmosphere is investigated with respect to the phase reactions during heat treatment of TiC/Si powders. Special attention is given to the production and decomposition of Ti₃SiC₂. Samples were heated in graphite and alumina furnaces, connected to a dilatometer which enabled in situ analysis of the phase reactions. The phase compositions of the heat treated samples were determined by X-ray diffraction. The reducing atmosphere of the graphite furnace enhanced the reactivity of the starting powder and enabled phase reactions to take place at a lower temperature than in the alumina furnace. TiSi₂ and SiC phases formed at temperatures below the melting point of Si and were continuously consumed at higher temperatures. Ti₃SiC₂ formed at the melting point of Si regardless of furnace atmosphere. No decomposition of the Ti₃SiC₂ was observed in either furnace.     

Effects of Mo addition on tribological performance of plasma-sprayed Ti–Si–C coatings

Ti–Si–C–Mo composite coatings were fabricated by plasma spraying using Ti, Si, graphite and Mo powders. The effect of Mo on microstructure and tribological performance of the Ti–Si–C coatings were investigated. The results showed that the Ti–Si–C coating consisted of TiC, Ti₃SiC₂, Ti₅Si₃, and residual graphite. The Ti–Si–C–Mo coatings consisted of TiC, Ti₃SiC₂, Ti₅Si₃, residual graphite, Mo and Mo₅Si₃ phases. With increasing Mo contents, the fractions of Mo and Mo₅Si₃ phases increased, and the fractions of Ti₃SiC₂ and Ti₅Si₃ phases decreased. All the coatings existed a typical lamellar structure. The addition of Mo enhanced the hardness and fracture toughness of Ti–Si–C coating by 16% and 52%, respectively. The coating porosity decreased by 57.6%. The wear resistance of the Ti–Si–C coating was also improved and the mass loss decreased by 83%. The wear mechanism of the Ti–Si–C–Mo coatings was the combination of abrasive wear, adhesive wear, and tribo-oxidation wear.     

Wetting and interfacial behavior of Al–Ti/4H–SiC system:A combined study of experiment and DFT simulation

Wetting and interfacial behavior of molten Al-(10, 20, 30, 40) at.%Ti alloys on C-terminated 4H–SiC at 1500 and 1550 °C were investigated experimentally, and theoretical bonding strength, structure stability and electronic structure of interfacial reaction products/C-terminated 4H–SiC interfaces were evaluated by first-principle calculations. The wetting experiments show that the Al–Ti/SiC systems present excellent wettability with contact angle of less than 15° except the Al–40Ti/SiC system performed at 1500 °C × 30 min. The SEM-EDS and TEM analyses demonstrate that the reaction products are mainly composed of Al₄C₃, TiC, Ti₃SiC₂, Ti₅Si₃C_X and τ phase, and their formation and evolution can be mainly affected by the Ti concentration in the Al–Ti alloys and wetting temperature. Moreover, the calculated results show that the SiC/C-terminated TiC interface presents the highest work of separation and its electronic property reveals that the localization of electrons and formation of covalent bond between interfacial C atoms lead to the excellent bonding strength of SiC/TiC interface.     

Ti3SiC2 interphase coating in SiCf/SiC composites: Effect of the coating fabrication atmosphere and temperature

The SiC fibers were coated with Ti₃SiC₂ interphase by dip-coating. The Ti₃SiC₂ coated fibers were heat-treated from 900 °C to 1100 °C in vacuum and argon atmospheres to comparatively analyze the effect of temperature and atmosphere on the microstructural evolution and mechanical strength of the fibers. The results show that the surface morphology of Ti₃SiC₂ coating is rough in vacuum and Ti₃SiC₂ is decomposed at 1100 °C. However, in argon atmosphere, the surface morphology is smooth and Ti₃SiC₂ is oxidized at 1000 °C and 1100 °C. At 1100 °C, Ti₃SiC₂ oxidized to form a thin layer of amorphous SiO₂ embedded with TiO₂ grains. Meanwhile, defects and pores appeared in the interphase scale. As a result, the fiber strength treated in the argon was lower than that treated in vacuum. The porous Ti₃SiC₂ interphase fabricated under vacuum was then employed to prepare the SiC_f/SiC mini composite by chemical vapor infiltration (CVI) combined with precursor infiltration pyrolysis (PIP), and can effectively improve the toughness of SiC_f/SiC mini composite. The propagating cracks can be deflected within the porous interphase layer, which promotes fiber pull-outs under the tensile strength.     

Mechanical Behavior and Electromagnetic Interference Shielding Properties of C/SiC–Ti3Si(Al)C2

In this paper, a low‐temperature densification process of Al–Si alloy infiltration was developed to fabricate C/SiC–Ti₃Si(Al)C₂, and then the microstructure, mechanical, and electromagnetic interference (EMI) shielding properties were studied compared with those of C/SiC–Ti₃SiC₂ and C/SiC–Si. The interbundle matrix of C/SiC–Ti₃Si(Al)C₂ is mainly composed of Ti₃Si(Al)C₂, which can bring various microdeformation mechanisms, high damage tolerance, and electrical conductivity, leading to the high effective volume fraction of loading fibers and electrical conductivity of C/SiC–Ti₃Si(Al)C₂. Therefore, C/SiC–Ti₃Si(Al)C₂ shows excellent bending strength of 556 MPa, fracture toughness 21.6 MPa·m^1/2, and EMI shielding effectiveness of 43.9 dB over the frequency of 8.2–12.4 GHz. Compared with C/SiC–Si and C/SiC–Ti₃SiC₂, both the improvement of mechanical properties and EMI shielding effectiveness can be obtained by the introduction of Ti₃Si(Al)C₂ into C/SiC, revealing great potential as structural and functional materials.     

Fabrication of Ti3SiC2-Ti4SiC3-SiC ceramic composites through carbosilicothermic reduction of TiO2

Dense Ti₃SiC₂-SiC, Ti₄SiC₃-SiC, and Ti₃SiC₂-Ti₄SiC₃-SiC ceramic composites were fabricated through carbosilicothermic reduction of TiO₂ under vacuum, followed by hot pressing of the as-synthesized products under 25 MPa at 1600°C. In the reduction step, SiC either alone or in combination with elemental Si was used as a reductant. A one-third excess of SiC was added in the reaction mixtures in order to ensure the presence of approximately 30 vol.% SiC in the products of synthesis. During the hot pressing step, the samples that contained Ti₃SiC₂ showed better densification compared to those containing Ti₄SiC₃. The obtained composites exhibited the strength properties typical of coarse-grained MAX-phase ceramics. The flexural strength values of 424 and 321 MPa were achieved in Ti₃SiC₂-SiC, and Ti₃SiC₂-Ti₄SiC₃-SiC composites, respectively. The fracture toughness values were 5.7 MPa·m^1/2.     

The thermal,electrical and mechanical properties of porous α-SiC ceramics bonded with Ti3SiC2 and β-SiC via low temperature in-situ reaction sintering

Porous SiC ceramics have recently attracted wide attention for their applications in the electrically heatable filter. Further improvement of the thermal and electrical conductivity without sacrificing permeability is a critical parameter for such applications. In the present work, porous SiC/Ti₃SiC₂ ceramic composites with Ti₃SiC₂ and micro/nano SiC have been prepared from TiC/Si/α-SiC mixtures at a low sintering temperature (1400 °C). Nano-laminated Ti₃SiC₂ enhanced the electrical conductivity, while the good thermal conductivity was achieved through in-situ formed nano β-SiC and raw coarse α-SiC in the porous ceramics. Along with the increase of initial α-SiC particle size from 0.76 to 16.13 μm, the permeability, thermal and electrical conductivity improved due to the decreased porosity and increased pore size in porous SiC/Ti₃SiC₂ ceramics. The results suggested that the decoupling of the electrical conductivity from the thermal conductivity could be tuned by adjusting the initial α-SiC particle size.     

In-situ fabrication of laminated SiC/TiSi2 and SiC/Ti3SiC2 ceramics by liquid silicon infiltration

The laminated silicon carbide/titanium silicon (SiC/TiSi₂) and silicon carbide/titanium silicon carbide (SiC/Ti₃SiC₂) ceramics were successfully designed and fabricated by liquid silicon (Si) infiltration. When the thickness of TiC layer was 150 and 450?µm, the TiSi₂ and Ti₃SiC₂ phases were the main products in the TiC layer, respectively. The as-fabricated structural unit of laminated SiC/Ti₃SiC₂ ceramics consisted of five layers of functionally graded materials, which has multiscale layered structure containing macro-layered structure and nano layered structure. The generation of hierarchical structure was attributed to the diffusion of Ti elements and in-situ formation of TiSi₂ and Ti₃SiC₂. The growth direction of Ti₃SiC₂ was anisotropic, thus providing more paths for the crack propagation via deflection, branching, and delamination during fracture process. However, the crack propagation inside the Ti₃SiC₂ phase included the pull out, bridging, lamination, deflection, and fracture of the single layer, which are the energy absorption and damage tolerance mechanisms of the Ti₃SiC₂ phase.     

Pore and microstructure change induced by SiC whiskers and particles in porous TiB2–TiC–Ti3SiC2 composites

TiB₂–TiC–Ti₃SiC₂ porous composites were prepared through a plasma heating reaction using powder mixtures of Ti, B₄C SiC whiskers (SiC_w) and SiC particles (SiC_p). The effects of the SiC_w and SiC_p content on pore structures, phase constituents, microstructure, and crystal morphology of TiC were studied. The results show that TiC, TiB, Ti₃B₄ phases are formed within the 5Ti+B₄C system. With the addition of SiC_w and SiC_p, the TiB and Ti₃B₄ phases are reduced, sometimes even disappeared. Interestingly, the content of TiB₂ and TiC increased, resulting in Ti₃SiC₂ and TiSi₂ being formed. The porosity of composites increases notably with the addition of SiC_w. However, with the increase of SiC_p, the porosity of the composites first decreases, followed by an increase. After adding the specified amount of SiC_w/SiC_p, the compressive strength of composites are improved significantly. Additionally, the pore size of the composites are decreased significantly with the addition of SiC_w/SiC_p. During the plasma heating process, some Si atoms will diffuse into the TiC lattice, which in turn made the cubic TiC grains into hexagonal lamellar TiC or Ti₃SiC₂ grains.     

Fabrication of Ti3SiC2 and Ti4SiC3 MAX phase ceramics through reduction of TiO2 with SiC

Ti₃SiC₂ and Ti₄SiC₃ MAX phase ceramics were fabricated through high-temperature vacuum reduction of TiO₂ using SiC as a reductant, followed by hot pressing of the products under 25 MPa of pressure at 1600 °C. It was found that both Ti₃SiC₂ and Ti₄SiC₃ may be obtained in good yields, depending on the annealing time during the reduction step. In addition to MAX phases, the products contained some amounts of TiC. The hot pressing step did not significantly affect the composition of the products, indicating good stability of Ti₃SiC₂ and Ti₄SiC₃ under these conditions. Analysis of the densification behavior of the samples revealed lower ductility in Ti₄SiC₃ compared to Ti₃SiC₂. The samples prepared herein exhibited the flexural strength, fracture toughness and microhardness typical of coarse-grained MAX-phase ceramics.     

Rapid synthesis of dense Ti3SiC2 by spark plasma sintering

Ti₃SiC₂ was rapidly synthesized and simultaneously consolidated from the starting mixture of Ti/Si/2TiC by spark plasma sintering (SPS). An intensive reaction leading to the formation of Ti₃SiC₂ occurred at the measured temperature of around 1200 °C, which is several hundreds degrees lower than that of conventional reactive hot pressing. The phase composition of the product could be tailored by adjusting the process parameters. An axisymmetric preferred orientation of the Ti₃SiC₂ grains with well-developed (008) planes was formed, resulting in an anisotropic hardness in respect to the textured product.     

Ti3Si(Al)C2-based ceramics fabricated by reactive melt infiltration with Al70Si30 alloy

Dense Ti₃Si(Al)C₂-based ceramics were synthesized using reactive melt infiltration (RMI) of Al₇₀Si₃₀ alloy into the porous TiC preforms. The effects of the infiltration temperature on the microstructure and mechanical properties of the synthesized composites were investigated. All the composites infiltrated at different temperatures were composed of Ti₃Si(Al)C₂, TiC, SiC, Ti(Al, Si)₃ and Al. With the increase of infiltration temperature from 1050 °C to 1500 °C, the Ti₃Si(Al)C₂ content increased to 52 vol.% and the TiC content decreased to 15 vol.%, and the Vickers hardness, flexural strength and fracture toughness of Ti₃Si(Al)C₂-based composite reached to 9.95 GPa, 328 MPa and 4.8 MPa m^1/2, respectively.