In-situ formation of Ti3SiC2 interphase in SiCf/SiC composites by molten salt synthesis

Titanium silicon carbide (Ti₃SiC₂) film was synthesized by molten salt synthesis route of titanium and silicon powder based on polymer-derived SiC fibre substrate. The pre-deposited pyrolytic carbon (PyC) coating on the fibre was utilized as the template and a reactant for Ti₃SiC₂ film. The morphology, microstructure and composition of the film product were characterized. Two Ti₃SiC₂ layers form the whole film, where the Ti₃SiC₂ grains have different features. The synthesis mechanism has been discussed from the thickness of PyC and the batching ratio of mixed powder respectively. Finally, the obtained Ti₃SiC₂ film was utilized as interphase to prepare the SiC fibre reinforced SiC matrix composites (SiC_f/Ti₃SiC₂/SiC composites). The flexural strength (σ_F) and fracture toughness (K_IC) of the SiC_f/Ti₃SiC₂/SiC composite is 460 ± 20 MPa and 16.8 ± 2.4 MPa?m^1/2 respectively.     

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.     

Synthesis of Ti3SiC2 MAX phase powder by a molten salt shielded synthesis (MS3) method in air

Titanium silicon carbide (Ti₃SiC₂) powder was synthesized by molten salt shielded synthesis route of elemental reactants. Potassium bromide (KBr) was used for gas-tight encapsulation of the consolidated reaction mixture for further high temperature processing. The synthesis of Ti₃SiC₂ powder was carried out in air, the salt cladding and molten salt pool provided for the protection of the material against oxidation both at low and high temperature. The process yielded free flowing Ti₃SiC₂ powders without the need of a milling step. Al addition to the reaction mixture resulted in a high purity (96 wt. %) of Ti₃SiC₂ at a synthesis temperature of 1250 °C. The synthesized micro-metric Ti₃SiC₂ can be milled to nano-metric powders.     

Synthesis of Ti3SiC2 MAX phase powder through molten salt method

Titanium silicon carbide (Ti₃SiC₂) MAX phase powder was synthesized from elemental reactants using the molten salt synthesis (MSS) method. Optimum experimental parameters were also investigated to determine the purity and synthesis pathway of the Ti₃SiC₂ MAX phase. The results showed that Ti₃SiC₂ was not synthesized using carbon black as the carbon source in the starting materials because of the high quantity of TiC formed along with the TiSi₂ silicide phase. However, Ti₃SiC₂ was successfully synthesized in a relatively high purity (93%) at 1200°C for 2 h using graphite as the source of carbon because of the formation of TiC and Ti₅Si₃ intermediate phases. The Ti₅Si₃ silicide phase was found to play a crucial role in the formation of the Ti₃SiC₂ MAX phase using the MSS method. Moreover, applying a pressure of 150 MPa to the prepared samples and using the eutectic mixture of NaCl–KCl (molar ratio: 1:1) instead of NaCl also resulted in the higher formation of the Ti₃SiC₂ MAX phase. The formation mechanism of Ti₃SiC₂ was determined to be the reaction among Ti₅Si₃, TiC, and residual carbon through the template-growth and dissolution–precipitation mechanisms that occurred at different stages of the synthesis process.     

Comparison of corrosion behavior of Ti3SiC2 and Ti3AlC2 in NaCl solutions with Ti

Corrosion behavior of self-sintered, ternary-layered titanium silicon carbide (Ti₃SiC₂) and titanium aluminum carbide (Ti₃AlC₂) fabricated by an in-situ solid-liquid reaction/hot pressing process was investigated by potentiodynamic polarization, potentiostatic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution. Commercially pure titanium (Ti) was selected for comparison through XRD, XPS, SEM and EDS examinations for elucidating both the passivation behavior and corrosion mechanism of the alloys. Both Ti₃SiC₂ and Ti₃AlC₂ exhibited significantly superior passivation characteristics compared to Ti; Ti₃SiC₂ also showed better corrosion resistance. The silicon/aluminum site is prone to attack, and the difference in the diffusion rate between the A-site atoms and titanium decreases the passivation ability of the MAX phase. CP titanium exhibited a lower passivation current density and did not undergo breakdown in the test potential region while two MAX phases are destroyed. Nevertheless, the corrosion resistances of Ti₃SiC₂ and Ti₃AlC₂ are comparable to that of CP titanium.     

Effect of the starting materials on the reaction synthesis of Ti3SiC2

Ternary carbide of titanium and silicon was produced via mechanical milling and following heat treatment. Effects of the starting materials, milling time and heat treatment temperature were studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to evaluate the structural and morphological evolutions of the ball-milled and annealed powders. Results showed that the ball milling of TiO–Si–C as the starting materials failed to synthesize Ti₃SiC₂. Additionally, ball milling the elemental powders for shorter milling times resulted in the activation of the powders. However, after longer milling times, Ti–TiC nanocomposite was obtained. Furthermore, during annealing the milled powders, Ti₃SiC₂–TiC nanocomposite with the mean grain size of 16 nm was synthesized. After 20 h of milling, a very fine microstructure with narrow size of distribution and spheroid particles was achieved.     

Synthesis of Ti3SiC2 by mechanically induced self-sustaining reaction: Some mechanistic aspects

Titanium silicon carbide Ti₃SiC₂ was prepared by mechanically induced self-sustaining reaction (MSR) in 3Ti/Si/2C powder blends. After mechanical alloying (MA) for 7 h, the MRS yielded the powdered and granulated products containing Ti₃SiC₂, TiC, TiSi₂, and Ti₅Si₃. Discussed are some important accompanying phenomena.     

Rapid fabrication of Al4SiC4 using a self-propagating high-temperature synthesis method

As a promising high-temperature ceramic, aluminum silicon carbide (Al₄SiC₄) has attracted much attention. Al₄SiC₄ is usually synthesized at high temperatures with a long reaction time in an electric furnace. Self-propagating high-temperature synthesis (SHS) is a promising technique for rapid synthesis. In this study, Al₄SiC₄ was prepared by the SHS method from a mixture of silicon, aluminum and carbon black with the addition of poly(tetrafluoroethylene) (PTFE) as an exothermic promoter. The experimental results showed that the use of a high-pressure Ar atmosphere could retain the gaseous materials in the pellet mixture, and the PTFE additive promoted the formation of silicon carbide. In addition, the oxide layer present on the surface of silicon particles inhibited the reaction between silicon and carbon. As a result, high-purity Al₄SiC₄ could be synthesized from aluminum, silicon, and carbon black with 15 wt% PTFE under 1.0 MPa Ar atmosphere in several seconds by the SHS method.     

Ti3SiC2 friction material prepared by novel method of infiltration sintering

Titanium silicon carbide (Ti₃SiC₂) is a remarkable friction material for its combination of the best properties of metals and ceramics. The high purity Ti₃SiC₂ ceramic has been prepared by infiltration sintering (IS), and the effect of a small amount of Si on Ti₃SiC₂ ceramic formation was investigated. The results show that the purity of Ti₃SiC₂ ceramic could be increased significantly and the sintering time for Ti₃SiC₂ could be decreased remarkably when proper amount of Si was added in the starting mixture. The Ti₃SiC₂ sintered compact with a purity of 99.2?wt-% and a relative density of 97% was obtained by the IS from a starting mixture composed of n(Ti):n(Si):n(TiC)?=?1:0.3:2 at 1500°C with holding time of 2/3?h.     

Synthesis and characterization of novel Ti3SiC2–cBN composites

In this paper, synthesis of novel super hard and high performance composites of titanium silicon carbide–cubic boron nitride (Ti₃SiC₂–cBN) was evaluated at three different conditions: (a) high pressure synthesis at ~ 4.5 GPa, (b) hot pressing at ~ 35 MPa, and (c) sintering under ambient pressure (0.1 MPa) in a tube furnace. From the analysis of experimental results, the authors report that the novel Ti₃SiC₂–cBN composites can be successfully fabricated at 1050 °C under a pressure of ~ 4.5 GPa from the mixture of Ti₃SiC₂ powders and cBN powders. The subsequent analysis of the microstructure and hardness studies indicates that these composites are promising candidates for super hard materials.     

Microstructural changes induced by low energy heavy ion irradiation in titanium silicon carbide

Low energy ion irradiation was used to investigate the microstructural modifications induced in Ti₃SiC₂ by nuclear collisions. Characterization of the microstructure of the pristine sample by electron back-scatter diffraction (EBSD) shows a strong texturing of TiSi₂, which is a common secondary phase present in Ti₃SiC₂. A methodology based on atomic force microscopy (AFM) was developed to measure the volume swelling induced by ion irradiation, and it was validated on irradiated silicon carbide. The swelling of Ti₃SiC₂ was estimated to 2.2 ± 0.8% for an irradiation dose of 4.3 dpa at room temperature. Results obtained by both EBSD and AFM analyses showed that nuclear collisions induce an anisotropic swelling in Ti₃SiC₂.     

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/SiC_p 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%.     

Green synthesis,formation mechanism and oxidation of Ti3SiC2 powder from bamboo charcoal,Ti and Si

Using low-cost and highly reactive bamboo charcoal, Ti and Si elemental powders as starting materials, Ti₃SiC₂ powder was synthesized via a simple and cost-efficient pressureless sintering technique in argon atmosphere. The influences of synthesis temperature, holding time and Si content on the Ti₃SiC₂ content of the synthesized products were investigated, and the analysis indicated that the relative content of Ti₃SiC₂ reached 98.9 wt% with a molar ratio of 3Ti/1.2Si/2.2C at 1400 °C for 1.5 h. The Ti₃SiC₂ with good crystallinity and homogeneous nanolayered structure was synthesized at lower temperatures due to the high reactivity and high specific surface area of bamboo charcoal. The non-isothermal oxidation behavior showed that Ti₃SiC₂ powder was stable in air below 540 °C. With the temperature increasing up to 1300 °C, continuous and dense TiO₂ and SiO₂ oxidation layers were formed on the surface of Ti₃SiC₂ particles, which conferred good oxidation resistance to Ti₃SiC₂ powder.     

Synthesis and reaction mechanism of Ti3SiC2 ternary compound by carbothermal reduction of TiO2 and SiO2 powder mixtures

The present study aims to investigate synthesis of Ti₃SiC₂ from TiO₂ and SiO₂ powder mixtures by carbothermal reduction method. Equilibrium TiO₂–SiO₂–C ternary phase diagram was used to predict the conditions for the formation of Ti₃SiC₂ at 1800 K under Ar atmosphere. A reactant mixture with a TiO₂:SiO₂ molar ratio of 1.5 and a C content of 68.75 mol% (26.86 wt%) was initially selected among the thermodynamically favorable reactant compositions for the experimental studies. Two different C sources, graphite flakes and pyrolytic C coating, were used to synthesize Ti₃SiC₂ at 1800 K under Ar atmosphere. When graphite flakes were used, the products contained a trace amount of Ti₃SiC₂ phase along with major TiC and minor SiC phases. Whereas, pyrolytic C coating on the oxide particles resulted in the products with much higher Ti₃SiC₂ contents owing to the close contact between the reactants. Optimal C concentration for the C coated oxide mixtures with a TiO₂:SiO₂ molar ratio of 1.5 was determined to be 30.05 wt% under the experimental conditions studied. Ti₃SiC₂ content of the products obtained from this reactant was observed to increase with reaction time to 31 wt% at 75 min beyond which it gradually decreased. XRD studies indicated that the product with the highest ternary carbide content also contained TiC and a trace amount of SiC. SEM-EDS analyses showed that this sample essentially consisted of spherical fine TiC particles and Ti₃SiC₂ nanolaminates. Equilibrium thermodynamic analysis of the TiO₂–SiO₂–C system suggested that the reaction of solid Ti₂O₃ with SiO and CO gases may play a dominant role in the formation of Ti₃SiC₂.     

Effects of Si source and high gravity on combustion synthesis of Ti3SiC2 in air

Abstract

Combustion synthesis of Ti₃SiC₂ was carried out in air with Si₃N₄, SiC, and Si as Si sources respectively, and the effect of Si source on the phase composition of the products was investigated. With Si₃N₄ as Si source, the major product was TiC_xN_1?x and no Ti₃SiC₂ was synthesised. When SiC and Si were used, Ti₃SiC₂ was synthesised. Such effect of Si source is thought to be connected with the formation mechanism of Ti₃SiC₂, where the presence of a Ti–Si melt is required. The combustion synthesis was also performed under high gravity condition instead of common gravity. The apparent density of the product prepared under high gravity was ～60% higher than that obtained under normal gravity. It is proposed that, the high gravity can facilitate the permeation of Ti–Si melt and enlarge the interface between the melt and carbide phases, which is helpful for the formation of Ti₃SiC₂.     

Factors affecting the property of porous Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript> metal ceramic fabricated through pressureless sintering

In this paper, micrometer-sized porous Ti₃SiC₂ metal ceramic was fabricated through a reactive synthesis method using titanium hydride, silicon and graphite elemental powders. The factors including raw powders, pressing pressure, sintering procedure affecting the purity and the pore property of porous Ti₃SiC₂ were systematically studied. The results indicate that the purity, pore property including maximum pore size and porosity can be effectively controlled by adjusting the synthesis parameters.     

Influence of Ti3SiC2 content on erosion behavior of Cu–Ti3SiC2 cathode under vacuum arc

In this study, a series of Cu–Ti₃SiC₂ composites with different Ti₃SiC₂ contents were prepared by spark plasma sintering. Their mechanical properties and electrical resistivity were investigated. Through analyzing the morphology and composition of the eroded regions, the effect of Ti₃SiC₂ content on the erosion behavior of Cu–Ti₃SiC₂ cathodes under vacuum arc was studied. Results show that the relative density and bending strength of the Cu–Ti₃SiC₂ composites decrease with the increasing Ti₃SiC₂ content, while the opposite holds for hardness and electrical resistivity. The morphology and phase composition of the erosion zone is dominated by the decomposition process and the amount of Ti₃SiC₂ in the cathode. Cu–Ti₃SiC₂ cathodes containing 10 mass%Ti₃SiC₂ or less displayed relatively flat eroded surface morphology. Cathodes with high Ti₃SiC₂ content suffered more serious erosion with voids, cracks, and severe decomposition of Ti₃SiC₂, all of which contribute to impairing the arc ablation resistance of the composite. Ti₃SiC₂ particles decomposed into TiC and Si vapor; eventually, this TiC also decomposed into Ti vapor and C, leaving a considerable amount of C on the arc affected cathode surface. Excess addition of Ti₃SiC₂ particles not only deteriorates the strength but also the electrical and thermal conductivity of the composite, both of which in turn harms the arc erosion resistance of the material. These results suggest that the optimal Ti₃SiC₂ content is below 10 mass% in the composite.     

Intermediate phases in synthesis of Ti3SiC2 and Ti3Si(Al)C2 solid solutions from elemental powders

In this paper, we investigated the reaction path to synthesize Ti₃SiC₂ by the in situ hot pressing/solid–liquid reaction method. The effect of different content of Al addition on this process was also examined. Ti₃SiC₂ mainly formed from the reaction between Ti₅Si₃C_x, TiC_x, TiSi₂ and graphite at 1400–1500 °C. As an inescapable impurity in Ti₃SiC₂, TiC_x was removed by addition of small amounts of Al. This was owing to the fact that the addition of a minor quantity of Al increased the amount of “effective TiC_x” and relatively decreased that of “invalid TiC_x”. Further increasing Al content, however, resulted in the presence of TiC_x again in the final product. This was due to the fact when significant amounts of Al was added, the stoichiometric ratio of silicon and graphite has been deviated from that for Ti₃SiC₂. More Si and less graphite were needed to prepare a monolithic Ti₃Si(Al)C₂ solid solution with high Al content.     

On the potential of polyetheretherketone matrix composites reinforced with ternary nanolaminates for tribological and biomedical applications

We report the synthesis and characterization of PEEK-MAX (Ti₃SiC₂, Ti₃AlC₂, and Cr₂AlC), and PEEK-MoAlB composites by hot-pressing. Detailed microstructure analysis by scanning electron microscopy showed that Ti₃SiC₂ particles are well dispersed in the PEEK matrix after the addition of 5 vol% Ti₃SiC₂ but at higher concentration (≥10 vol%), the Ti₃SiC₂ particles segregated at the phase boundaries and formed interpenetrating micro-networks. PEEK-Ti₃AlC₂ and PEEK-MoAlB composites also showed similar structuring at the microstructural level. PEEK-Cr₂AlC composites showed a different behavior where Cr₂AlC particles were well dispersed in the PEEK matrix. All the three PEEK-MAX composites have lower hardness than PEEK-MoAlB composites as MoAlB particulates are appreciably harder than MAX phases but were harder than PEEK. Due to heterogenous nucleation, the addition of MAX phases or MoAlB reduced the crystallization temperature (T_c) by a few ^oC. The formation of imperfect crystals also resulted in the lowering of melting point (T_m) of these composites. PEEK reinforced with 10 vol% Ti₃SiC₂, Ti₃AlC₂ and MoAlB showed plastic failure, and had higher strength than PEEK. Comparatively, PEEK reinforced with 10 vol% Cr₂AlC did not show any enhancement. All the PEEK-MAX and PEEK-MoAlB composites showed triboactive behavior and enhanced wear resistance.     

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.