A new synthesis reaction of Ti3SiC2 from Ti/TiSi2/TiC powder mixtures through pulse discharge sintering (PDS) technique

Ti/TiSi₂/TiC powder mixtures with molar ratios of 1:1:4 (M1) and 1:1:3 (M2) were first employed for the synthesis of Ti₃SiC₂ through pulse discharge sintering (PDS) technique in a temperature range of 1100–1325 °C. It was found that Ti₃SiC₂ phase began to form at the temperature above 1200 °C and its purity did not show obvious dependence on the sintering temperature at 1225–1325 °C. The TiC contents in M2 samples is always lower than that of the M1 samples, and the lowest TiC contents in the M1 and M2 samples were calculated to be about 7 wt% and 5 wt% when the sintering was conducted at the temperature near 1300 °C for 15 minutes. The relative density of the M1 samples is always higher than 99% at sintering temperature above 1225 °C, indicating a good densification effect produced by the PDS technique. A solid-liquid reaction mechanism between Ti-Si liquid phase and TiC particles was proposed to explain the rapid formation of Ti₃SiC₂. Furthermore, it is suggested that Ti/TiSi₂/TiC powder can be regarded as a new mixture to fabricate ternary carbide Ti₃SiC₂. Received: 5 September 2001 / Accepted: 11 September 2001     

Fabrication of Monolithic Ti3SiC2 Ceramic Through Reactive Sintering of Ti/Si/2TiC

Fabrication of monolithic Ti₃SiC₂ has been investigated through the route of reactive sintering of Ti/Si/2TiC mixtures. Significant phase differences existed between the surface and the interior of as-synthesized products due to the evaporation of Si during the reaction process. The use of a 3Ti/SiC/C mixture as a powder bed could control the evaporation of Si and develop monolithic Ti₃SiC₂. A reaction model for the formation of Ti₃SiC₂ in the Ti/Si/2TiC system is discussed.On leave from     

Formation of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript> from Ti-Si-TiC powders by pulse discharge sintering (PDS) technique

Ti/Si/TiC powder mixture with molar ratios of 2:2:3 were sintered at various temperatures from 700–1300 °C for 15 min by PDS technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for the evaluation of phase composition in different samples for the understanding of the sintering mechanism for this system. Results showed that Ti₅Si₃ formed as the intermediate phase during sintering. The reaction between Ti₅Si₃ and TiC as well as Si induces the formation of Ti₃SiC₂, and TiSi₂ appears as the byproduct in this process. At temperature above 1000 °C, TiSi₂ reacts with TiC to form Ti₃SiC₂. High Ti₃SiC₂ phase content bulk material can be synthesized at 1300 °C for 15 min.     

Synthesis and high temperature mechanical properties of Ti3SiC2/SiC composite

A high density Ti₃SiC₂/20 vol % SiC composite was hot pressed under a uniaxial pressure of 45 MPa for 30 min in an Ar atmosphere at 1600 °C. The grain size of the Ti₃SiC₂/SiC composite was finer than that of monolithic Ti₃SiC₂, though the composite was hot pressed at a higher temperature, due to the dispersion of SiC particles in the Ti₃SiC₂ matrix. Room temperature fracture toughness of the composite and Vickers hardness were measured as 5.4 MPa m^1/2 and 1080 kg mm^–2, respectively. A higher flexure strength of the composite compared to that of monolithic Ti₃SiC₂ was measured both at room temperature and up to 1200 °C. At 1000 °C, the composite showed a lower oxidation rate than that of monolithic Ti₃SiC₂.     

Effects of infiltration parameters on the synthesis of nano-laminated Ti3SiC2

In this paper, the nano-laminated Ti₃SiC₂ ceramics were fabricated by liquid silicon infiltration of gelcast porous titanium carbide (TiC) preforms. The phase compositions and microstructures of the synthesized samples at various infiltration times and temperatures were analyzed by the X-ray diffraction (XRD) technique and were observed by field emission scanning electron microscopy (FESEM). The results showed that the formed Ti₃SiC₂ decomposes to the TiC phase with the increase of infiltration time. It was found from the XRD patterns that the samples with an 88?wt% Ti₃SiC₂ MAX phase can be produced with infiltration at 1500°C for 1?h with 50 vol% solid loading and 10?wt% monomer content. It is found that the hardness and flexural strength of Ti₃SiC₂-based ceramic has been reduced with a decrease in SiC and TiC impurities and reach 5.8?GPa and 420?MPa, respectively, for the sample with 15?wt% impurity. The microstructure evaluation revealed that the purity and properties of samples were affected both through the gelcasting and infiltration parameters.     

Synthesis and phase evolution of Si-C-Ti powder derived from poly(methylsilaacetylene) and Ti

Si-C-Ti powder was synthesized by reactive pyrolysis of poly(methylsilaacetylene)(PSCC) precursor mixed with metal Ti powder. Pyrolysis of PSCC/Ti mixture with certain atomic ratio was carried out in argon atmosphere between 1300 °C and 1500 °C. The metal-precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy equipped with EDX. Ti₃SiC₂ phase was obtained from reaction of PSCC and Ti for the first time. Ti₃SiC₂ formation started at 1300 °C and its amount increased significantly at 1400 °C. In addition, liquid formed by additive CaF₂ could promote the formation of Ti₃SiC₂ phase.     

Oxidation behavior of silicide coating on Ti3SiC2-based ceramic

A silicide coating was prepared on Ti₃SiC₂-based ceramic by pack cementation to improve the oxidation resistance of Ti₃SiC₂, which is a technologically important material for high temperature applications. The microstructure, phase composition and oxidation resistance of the coated sample were investigated. The results demonstrated that the silicide coating was mainly composed of TiSi₂ and SiC. A single layer of a mixture of SiO₂ and TiO₂ was formed on the surface of the coated sample during isothermal oxidation at 1100 °C and 1200 °C for 20h. Compared to Ti₃SiC₂, the parabolic rate constant of silicide coated Ti₃SiC₂ decreased by 2~3 orders of magnitude. Furthermore, the coated sample showed much better cyclic oxidation resistance than Ti₃SiC₂ during the cyclic oxidation at 1100 °C for 400 times. However, during the preparation of the coating, a number of fine cracks formed in the outer layer of the coating. When these cracks penetrated the whole coating during the cyclic oxidation, the oxidation rate was accelerated, which degraded the oxidation resistance. Electronic Publication     

Synthesis and phases evolution of Si–C–Ti from polycarbosilane (PCS) and metal Ti

Si–C–Ti ceramics were synthesized by reactive pyrolysis of polycarbosilane (PCS) precursor filled with metal Ti powder. Pyrolysis of mixture with atomic ratio of Ti:Si through 3:1–3:2 was carried out in argon atmosphere at given temperature up to 1500 °C. The metal–precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy with EDX. The Ti₃SiC₂ phase was obtained firstly from reaction of PCS and Ti. Ti₃SiC₂ formation starts at 1300 °C and its amount increases significantly in a narrow temperature range between 1400 °C and 1500 °C. In addition, addition of CaF₂ can promote the formation of Ti₃SiC₂ phase.     

Fabrication and characterization of Ti3SiC2-SiC nanocomposite by in situ reaction synthesis of TiC/Si/Al powders

The microstructure and mechanical properties of Ti₃SiC₂-SiC nanocomposite fabricated by in situ hot pressing (HP) synthesis process were studied. The results show that dense Ti₃SiC₂-SiC composite contained minor TiSi₂ obtained by hot sintering at 1350°C for 1 h. The average grain size of Ti₃SiC₂ was 4 μm in length, and the size of SiC grains is about 100 nm. With its fine microstructure, the Ti₃SiC₂-SiC nanocomposite shows good mechanical properties.     

Mechanical and Electromagnetic Interference Shielding Behavior of C/SiC Composite Containing Ti3SiC2

In order to obtain the composites with the integration of structural and functional properties, Ti₃SiC₂ is introduced into C/SiC due to its excellent damage tolerance and electromagnetic interference (EMI) shielding properties. C/SiC–Ti₃SiC₂ has the lower tensile strength, while the higher compressive strength than C/SiC. The penetration energy of C/SiC–Ti₃SiC₂ in the impact experiment is improved at least three times than that of C/SiC, resulting from the improved damage tolerance. With the introduction of Ti₃SiC₂, the EMI shielding effectiveness increases from 31 to 41 dB in X‐band (8.2 to 12.8 GHz) due to the increase of electrical conductivity. C/SiC–Ti₃SiC₂ reveals the great potential as structural and functional materials based on the multi‐functional properties.

     

Fabrication of highly dense Ti3SiC2 ceramics by pressureless sintering of mechanically alloyed elemental powders

Pressureless sintering of Ti₃SiC₂ ceramics has been investigated by using mechanically alloyed elemental Ti, Si and C powder mixture as the starting materials. It has been found that mechanical alloying enhanced both the formation of Ti₃SiC₂ phase and the densification during sintering process. Highly dense Ti₃SiC₂ ceramics with a relative density up to 99% and a phase purity of 80% Ti₃SiC₂ (TiC_x as the secondary phase) were obtained by sintering the mechanically alloyed powders at relatively low temperatures near 1773 K in an argon atmosphere of 0.1 MPa. The physical properties of the present pressureless-sintered Ti₃SiC₂-based ceramics are comparable to those of nearly single phase Ti₃SiC₂ ceramics fabricated by the reactive hot-isostatic pressing (HIP) that had been used so far.     

Fluctuation synthesis and characterization of Ti3SiC2 powders

 A novel fluctuation method for the synthesis of Ti₃SiC₂ powders was developed. The raw materials used in this process are Ti, Si, and graphite powders. Fluctuation synthesis utilized Si as in-situ liquid forming phase (additive), which was formed by heating the powder mixtures to 1300°C and using the heat released from the exothermic reaction for Ti₃SiC₂ formation. The result demonstrated that the reaction time for the formation of Ti₃SiC₂ was dramatically shortened using fluctuation method and the powders produced using this method contained more than twice amount of Ti₃SiC₂ compared to the solid reaction synthesized powders. The powders prepared by fluctuation method are fiber-like in morphology with dimensions of 0.8–2 μm in width and 5–10 μm in length. The growth direction of the fiber-like Ti₃SiC₂ particulate is {101^–1}*. The lattice parameters for Ti₃SiC₂ were determined by a trial-and-error method and are a=3.067 ? and c=17.645 ?. Received: 28 September 1998 / Reviewed and accepted: 1 October 1998     

Synthesis and some properties of Ti3SiC2 by hot pressing of Ti,Si and C powders Part 2 – Mechanical and other properties of Ti3SiC2

Abstract

Some properties of the remarkable Ti₃SiC₂ based ceramic synthesised by hot pressing of elemental Ti, Si, and C powders have been investigated. Its flexural strength by using three point bending tests and fracture toughness by using single edge notched beam tests were measured at room temperature to be in the range 310–427 MPa and about 7·MPa m^1/2, respectively. This material is a relative 'soft' ceramic with a low hardness of 4 GPa. Ti₃SiC₂ is similar to the soft metals and is a damage tolerant material that is able to contain the extent of microdamage. An oxidation test has been performed in the temperature range 1000–1400°C in air for 20 h. The oxidation resistance below 1100°C was good. Two oxidized layers were formed, the outer layer consisting of pure rutile-type TiO₂, and the inner layer a mixture of SiO₂ and TiO₂. The average coefficient of thermal expansion (CTE) of Ti₃SiC₂ was measured to be 9·29 × 10^?6 K^?1 in the temperature range 25–1400°C. The thermal shock resistance of Ti₃SiC₂ was evaluated by quenching the samples from 800°C, 1200°C, and 1400°C, respectively. The retained flexural strength drops dramatically at quenching temperature, but shows a slight increase after quenching from 1400°C compared with quenching from 800°C and 1200°C.     

Microstructure and thermal expansion of Ti3SiC2

Abstract

A dense, bulk ceramic of Ti₃SiC₂ containing impurities of TiC and Ti₅Si₃ was fabricated by hot pressing elemental powders of Ti, Si, and C. X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy were used to determine the crystalline phases and observe the microstructure of sintered compacts, respectively. Ti₃SiC₂ exhibits anisotropic grain growth and the size of exaggerated grain is ~25 μm in length. The average coefficient of thermal expansion of Ti₃SiC₂ was measured to be 9.29 × 10^-6 K^-1 in the temperature range 25-1400°C.     

Phase stability of SiC against Ti at high temperature

SiC to SiC were reacted by Ti foil at high temperature of 1673 K in vacuum. Ti reacted with SiC, and formed many reaction phases between SiC and Ti. At 1673 K SiC reacted at a reaction time of 0.5 ks or longer. From the SiC many reaction zones of Ti₃SiC₂, Ti₅Si₃C_X, Ti₅Si₃C_X + TiC, and TiC + Ti were formed. Ti binary compound of TiC and Ti ternary compounds of Ti₃SiC₂, and Ti₅Si₃C_X, were formed. The principle of the reaction zones was thermodynamically discussed by the corresponding chemical potential diagram.     

Polycarbosilane derived Ti3SiC2

Titanium silicon carbide (Ti₃SiC₂) ceramic was synthesized by in-situ reaction of metal titanium and polycarbosilane. Reaction mechanisms which lead to the formation of Ti₃SiC₂ were suggested on the basis of XRD analysis. The content of Ti₃SiC₂ reached 93% in products obtained from heating the Ti/polycarbosilane green compact at 1400 °C in Ar. The morphology and compositions of the products were examined by SEM equipped with EDX. The typical laminate structure of Ti₃SiC₂ particles with 1-4 μm in thickness and 4-15 μm in length was observed. EDX results showed that the atomic ratio of Ti:Si:C of grains is close to 3:1:2, which agrees with Ti₃SiC₂ composition.     

Effect of Aluminum on Synthesis of Ti3SiC2 by Spark Plasma Sintering (SPS) from Elemental Powders

The effect of aluminum on synthesis of Ti₃SiC₂ by spark plasma sintering (SPS) from elemental powders was investigated in this paper. X-ray diffraction patterns and scanning electron microscopy photographs of samples with different content of aluminum indicated that proper addition of aluminum both favored the formation and accelerated the crystal growth of Ti₃SiC₂. The process parameters in the sintering course revealed that addition of aluminum decreased the temperature for the synthesis reaction of Ti₃SiC₂. Polycrystalline bulk Ti₃SiC₂ material with high purity and density could be fabricated by spark plasma sintering from the elemental powder mixture with starting composition of Ti₃Si_1–xAl_xC₂, where x = 0.05–0.2. SEM photographs showed Ti₃SiC₂ synthesized from elemental powders was in plane-shape with a size of about 10–20 µm in the elongated dimension. Solid solution of aluminum decreased the thermal stability of Ti₃SiC₂ and made the temperature at which Ti₃SiC₂ decomposed be as low as 1300°C.     

Dense Ti3SiC2 prepared by reactive HIP

The dense polycrystalline Ti₃SiC₂ has been synthesized by reactive HIPing of Ti, SiC and C powders. The bulk material with the highest Ti₃SiC₂ content about 97 vol % was obtained when treated at 1500°C, 40 MPa for 30 min. The density was 99% of the theoretical value. The Ti₃SiC₂ grains had the columnar and plate-like shapes. The grains were well boned to form a network structure. Many stacking faults were observed along the (001) plane of Ti₃SiC₂. The Vickers hardness, Young's modulus, flexural strength and fracture toughness were 4 GPa, 283 GPa, 410 MPa and 11.2 MPa m^1/2, respectively. The Ti₃SiC₂ was stable up to 1100°C in air. The electrical resistivity was 2.7×10^–7 ·m at room temperature. The resistivity increased linearly with the increasing temperature. It may be attributed to a second order phase transition. The Seebeck coefficient was from 4 to 20 V/K in the temperature range 300–1200 K. It seems that Ti₃SiC₂ is semi-metallic with hole carriers from this small positive value.     

Preparation of Ti3SiC2

Phase relations in the Ti-C-SiC system are studied with the aim of optimizing Ti₃SiC₂ synthesis. The optimal starting-mixture compositions for the synthesis of phase-pure Ti₃SiC₂ powder can be represented by the formula 3Ti + (1 ? z)C + (1 + z)SiC, where z = 0.2–0.6. In the temperature range 1630–1670 K under dynamic vacuum, the excess silicon vaporizes from the sample. The processes leading to the formation of impurity phases are discussed.     

Joining of SiC ceramic-based materials with ternary carbide Ti3SiC2

The joining of two pieces of SiC-based ceramic materials (SiC or C_f/SiC composite) was conducted using Ti₃SiC₂ as filler in vacuum in the joining temperatures range from 1200 °C to 1600 °C. The similar chemical reactions took place at the interface between Ti₃SiC₂ and SiC or C_f/SiC, and became more complete with joining temperature increases, and with the consequent increased joining strengths of the SiC and C_f/SiC joints. Based on the XRD and SEM analyses, it turns out that two reasons are most important for the high joining strengths of the SiC and C_f/SiC joints. One is the development of layered Ti₃SiC₂ ceramic, which has plasticity in nature and can contribute to thermal stress relaxation of the joints; the other is the chemical reactions between Ti₃SiC₂ and the base materials which result in good interface bonding.