High-temperature dielectric and electromagnetic interference shielding properties of SiCf/SiC composites using Ti3SiC2 as inert filler

Ti₃SiC₂ filler has been introduced into SiC_f/SiC composites by precursor infiltration and pyrolysis (PIP) process to optimize the dielectric properties for electromagnetic interference (EMI) shielding applications in the temperatures of 25–600 °C at 8.2–12.4 GHz. Results indicate that the flexural strength of SiC_f/SiC composites is improved from 217 MPa to 295 MPa after incorporating the filler. Both the complex permittivity and tan δ of the composites show obvious temperature-dependent behavior and increase with the increasing temperatures. The absorption, reflection and total shielding effectiveness of the composites with Ti₃SiC₂ filler are enhanced from 13 dB, 7 dB and 20 dB to 24 dB, 21 dB and 45 dB respectively with the temperatures increase from 25 °C to 600 °C. The mechanisms for the corresponding enhancements are also proposed. The superior absorption shielding effectiveness is the dominant EMI shielding mechanism. The optimized EMI shielding properties suggest their potentials for the future shielding applications at temperatures from 25 °C to 600 °C.     

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.     

Complex permittivity and electromagnetic interference shielding properties of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>/polyaniline composites

Ti₃SiC₂/insulating polyaniline (Ti₃SiC₂/PANI) composites were prepared by solution blending and subsequently by hot-pressing process. The dielectric permittivity and electromagnetic interference (EMI) shielding effectiveness (SE) of the composites were determined in the frequency range of 8.2–12.4 GHz (X-band). Both real and imaginary permittivities increase with the increasing Ti₃SiC₂ content, and which are attributed to the enhanced displacement current and conduction current. The EMI SE of the composites can be greatly improved by addition of Ti₃SiC₂ filler, which may be ascribed to the increase of electrical conductivity of the composites. It is also found that the reflection of electromagnetic radiation is a dominant mechanism for EMI shielding of the composite. An average EMI SE of 23 dB can be achieved in the X-band range for the composite with 25 wt% Ti₃SiC₂ content, which shows the potential of the Ti₃SiC₂/PANI composites as EMI shielding materials for commercial applications.     

Low temperature synthesis of Ti3 SiC2 from Ti/SiC/C powders

Abstract

Ternary carbide Ti₃ SiC₂ was first synthesised through a pulse discharge sintering (PDS) technique from mixtures of Ti, SiC, and C with different molar ratios. Sintering processes were conducted at 1200 – 1400°C for 15 – 60 min at a pressure of 50 MPa. The phase constituents and microstructures of the synthesised samples were analysed by X-ray diffraction (XRD) technique and observed by scanning electron microscopy (SEM). The results showed that, for samples sintered from 3Ti/SiC/C powder at 1200 – 1400°C, TiC is always the main phase and only little Ti₃ SiC₂ phase is formed. When the molar ratios Ti : SiC : C were adjusted to 3 : 1.1 : 2 and 5 : 2 : 1, the purity of Ti₃ SiC₂ in the synthesised samples was improved to about 93 wt-%. The optimum sintering temperature for Ti₃ SiC₂ samples was found to be in the range 1250 – 1300°C and all the synthesised samples contain platelike grains. The relative density of Ti₃ SiC₂ samples was measured to be higher than 99% at sintering temperatures above 1300?C. It is suggested that the PDS technique can rapidly synthesise ternary carbide Ti₃ SiC₂ with good densification at lower sintering temperature.     

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.     

Microstructure and mechanism of damage tolerance for Ti3SiC2 bulk ceramics

 Titanium silicon carbide (Ti₃SiC₂) is a damage tolerance material that is expected to be used in a number of high temperature applications. In this work, the microstructure and damage tolerance mechanism of Ti₃SiC₂ was investigated. The result demonstrated that the Ti₃SiC₂ ceramics prepared by the in-situ hot pressing/solid-liquid reaction process had a dual microstructure, i.e., large laminated grains were distributed within small equiaxial grains. This microstructure is analogous to that of platelets reinforced ceramic matrix composites. The bending test using single-edge-notched-beam specimens revealed that Ti₃SiC₂ was a damage tolerance material. The damage tolerance mechanisms for Ti₃SiC₂ are basal plane slip, grain buckling, crack deflection, crack branching, pull-out and delamination of the laminated grains. Received: 7 December 1998/Reviewed and accepted: 15 December 1998     

Polyaryletherketone polymer nanocomposite engineered with nanolaminated Ti3SiC2 ceramic fillers

Thermal, mechanical and tribological properties of a new ceramic–polymer nanocomposite in which polyaryletherketone (PAEK) polymer was reinforced with titanium silicon carbide (Ti₃SiC₂), a ceramic nanolaminate belonging to the MAX phase family (M is an early transition metal, A represents group IIIA or IVA element and X is either carbon and/or nitrogen) are reported for the first time. PAEK–Ti₃SiC₂ nanocomposites with varying volume fractions of Ti₃SiC₂ were processed by hot pressing. The effect of Ti₃SiC₂ on the thermal expansion, bulk hardness, mechanical strength, wear and friction properties was systematically analyzed and the results are discussed. The study confirms that the Ti₃SiC₂ controlled the high thermal expansion property of PAEK polymer. In addition to that, it enhanced the wear resistance and mechanical strength of PAEK without affecting its inherent low-friction characteristics.     

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.     

Electromagnetic interference shielding effectiveness of SiCf/SiC composites with PIP–SiC interphase after thermal oxidation in air

SiC_f/SiC composites with PIP–SiC interphase were prepared as electromagnetic interference (EMI) shielding materials by chemical vapor infiltration method. Effects of thermal oxidation on electrical and EMI shielding properties of the composites in X band were investigated. The as-received composites show high electrical conductivity of 0.12 S/cm and SE_T value of 29 dB, which is ascribed to the free carbon in the composites. The electrical conductivities and weight retentions of the composites decrease with oxidation temperatures or time increase. Likewise, the shielding properties deteriorate to some degree but the SE_T value exhibits more than 17 dB after oxidation at 1000 °C for 2 h and 15 dB at 900 °C for 6 h, respectively. The deterioration of electrical and EMI shielding properties during oxidation process is ascribed to the consumption of free carbon. The high SE_A value and low SE_R value imply that absorption is the dominant EMI shielding mechanism. The SiC interphase can protect the fibers and keep EMI shielding properties of the composites at a high level.     

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.     

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.     

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.     

Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>/TiC composites prepared by PDS

Synthesis of composite materials with improved mechanical properties is considered. Pulse discharge sintering (PDS) technique was utilized for consolidation and synthesis of double phase Ti₃SiC₂/TiC composites from the initial powders TiH₂/SiC/TiC. Scanning electron microscopy with energy-dispersive spectrometry (SEM with EDS) and X-ray diffractometry (XRD) were exploited for the analysis of the microstructure and composition of the sintered specimens. Mechanical tests showed high bending and compression strength and low Vickers hardness of Ti₃SiC₂-rich specimens. The reasons of this behaviour are in the features of the textured microstructure of Ti₃SiC₂ phase.     

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     

Cu/Ti3SiC2 composite: a new electrofriction material

 Cu/Ti₃SiC₂ composite, a new electrofriction material, was prepared, for the first time, by PM method. The microstructure, mechanical and electrical properties of the Cu/Ti₃SiC₂ composites were investigated and were compared with those of Cu/graphite composites. The results demonstrated that Cu/Ti₃SiC₂ composites had superior mechanical properties over Cu/graphite composites. At filer content of less than 20 vol%, the electrical conductivity for Cu/Ti₃SiC₂ composites was higher than that for Cu/graphite composites; at high filer content, the electrical conductivity for Cu/Ti₃SiC₂ composites was lower than that for Cu/graphite composites because of the presence of residual pores. It was found that like Cu/graphite composite, Cu/Ti₃SiC₂ was a self-lubricated material. The compressive yield strength, Brinell hardness, relative ratio of compressive for Cu-30 vol% Ti₃SiC₂ composites are 307 MPa, 140, 15.7% respectively. Received: 29 December 1998/Accepted: 15 February 1999     

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.     

Preparation of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript> through reduction of titanium dioxide with silicon carbide

This paper describes the reduction of titanium dioxide with a mixture of silicon carbide and silicon powders at a temperature of 1550°C under vacuum. It has been shown that the use of the combined reductant enables the preparation of the ternary phase Ti₃SiC₂ through concurrent carboand silicothermic processes. The optimal compositions for Ti₃SiC₂ formation are TiO₂ + (1.5–x)SiC + 2xSi with x = 0.4–0.5. The Ti₃SiC₂ yield then reaches 96 wt %.     

Temperature fluctuation/hot pressing synthesis of Ti3SiC2

A novel temperature fluctuation synthesis and simultaneous densification process for the preparation of Ti₃SiC₂ was developed. The advantages of this novel method include low synthesis temperature, short reaction time and simultaneous densification. The microstructure and room temperature mechanical properties of the Ti₃SiC₂ synthesized using this method were investigated. The result demonstrated that the Ti₃SiC₂ ceramic consisted of mainly laminated grains. It was found, with the aid of computer simulated crystallite shape, that the laminated Ti₃SiC₂ grains were composed of thin hexagonal plates. These laminated grains characterized the Ti₃SiC₂, and were responsible for the mechanical properties of the polycrystalline Ti₃SiC₂ ceramic. The measured flexural strength and the fracture toughness were 470 ± 26 MPa and 7.0 ± 0.2 MPa·m^1/2, respectively. The high toughness was attributed to the contribution of crack deflection, crack bridging, delaminating and grain pull-out of laminated Ti₃SiC₂.     

Bonding mechanism between silicon carbide and thin foils of reactive metals

Pressureless-sintered SiC pieces and SiC single crystals were joined with foils of reactive metals at 1500° C (1773 K) for titanium and zirconium foils or at 1000° C (1273 K) for Al/Ti/Al foils. Bend testing at various temperatures up to 1400° C (1673 K), optical and electron microscopy, and electron-probe X-ray microanalysis studies were carried out on the specimens. From the results, it was concluded that the fairly high bond strength of titanium-foil joined SiC specimens might be attributed to the formation of a Ti₃SiC₂ compound, since good lattice matching between SiC and Ti₃SiC₂ was obtained in the SiC single crystals. Also in the Al/Ti/Al-foil joined SiC, high bond strength was obtained, but it decreased steeply at 600° C (873 K) because of a retained aluminium phase. The bond strength in the zirconium-foil joined SiC was low.     

Evaluation on diffusion bonded joints of TiAl alloy to Ti3SiC2 ceramic with and without Ni interlayer: Interfacial microstructure and mechanical properties

Diffusion bonding of TiAl alloys and Ti₃SiC₂ ceramics were carried out in a vacuum atmosphere. The microstructures and mechanical properties of the bonded joints were investigated. Results showed that three coherent intermetallic layers formed in the TiAl/Ti₃SiC₂ joints during bonding process. The compound layer adjacent to Ti₃SiC₂ substrate was indicated to be Ti₅Si₃, in which brittle fracture of the joints took place during shear strength test. The properties of diffusion bonded joints were greatly improved attributed to the formation of a good transition in the joint as well as the relief of the residual stress when using Ni foil as interlayer. Formation mechanisms of the compound layers during bonding process were discussed. Shear test results showed that the maximum shear strength reached 52.3 MPa. Corresponding fractograph indicated that the crack mainly propagated along Ti₃SiC₂ substrate adjacent to the bonding zone, accompanied with an intergranular and transgranular fracture mode.