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.     

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.     

Ceramic composite Ti3SiC2–TiB2—Microstructure and mechanical properties

The structure and properties of Ti₃SiC₂–TiB₂ ceramic composites were investigated. A computer-aided image analysis, tests of mechanical properties as well as observation of the crack propagation mechanism were carried out for the Ti₃SiC₂–TiB₂ composite at a TiB₂ dispersed phase content varying from 5% to 50% by volume. The resulting data obtained made it possible to determine a relation between the TiB₂ content and the mechanical properties of the composite; moreover, they revealed the way in which the presence of TiB₂ particles in the composite matrix affected the course of cracks in the composite.     

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.

     

Friction and wear behavior of polytetrafluoroethene composites filled with Ti3SiC2

In this work, polytetrafluoroethylene (PTFE) composites filled with Ti₃SiC₂ or graphite were prepared through powder metallurgy. The effects of different filling components, loads and sliding velocities on the friction performance of Ti₃SiC₂/PTFE composites were studied. Ti₃SiC₂/PTFE composites exhibit better wear resistance than graphite/PTFE composites due to the better mechanical properties of Ti₃SiC₂. The wear resistance was found to improve around 100× over unfilled PTFE with the addition of 1 wt.% Ti₃SiC₂. In addition, the 10 wt.% sample had the lowest wear rate of K = 2.1 × 10⁻⁶ mm³/Nm and the lowest steady friction coefficient with μ = 0.155 at the condition of 90 N–0.4 m/s. Ti₃SiC₂ was proved to promote the formation of a thin and uniform transfer film on counterpart surface and a protection oxide film on worn surface, which are the key roles for improving wear resistance.     

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     

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.     

Influence of Ti3SiC2 content on tribological properties of NiAl matrix self-lubricating composites

NiAl matrix self-lubricating composites (NMCs) with various contents of Ti₃SiC₂ were fabricated by in situ technique using spark plasma sintering. The effects of Ti₃SiC₂ content on tribological properties of NMC were investigated. The results showed that NMC were composed of the matrix phase of NiAl alloy, enhanced phase of TiC and lubricating phases of Ti₃SiC₂ and C. NMC with 10 wt.% Ti₃SiC₂ exhibited low friction coefficient of 0.60 and wear rate of 5.45 × 10⁻⁵ mm³ (N m)⁻¹ at the condition of 10 N–0.234 m/s at room temperature. The optimum content of Ti₃SiC₂ was 10 wt.%. The excellent tribological performance of NMC could be attributed to the balance between strength and lubricity, as well as synergetic effect of enhanced phase and lubricating phases. The wear mechanisms changed with the increasing of the doped content of Ti₃SiC₂.     

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.     

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.     

Crystallographic relations between Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript> and TiC

Ti₃SiC₂ is a so-called not-so-brittle ceramic that combines the merits of both metals and ceramics. However, many previous works demonstrated that its bonding nature and properties were strongly related to TiC. In this paper the crystallographic relations between Ti₃SiC₂ and TiC were established and described based on the transmission electron microscopy investigation on the Ti₃SiC₂/TiC interface in Ti₃SiC₂ based material. At Ti₃SiC₂/TiC interface, the following crystallographic relationships were identified: (111)TiC//(001)Ti₃SiC₂, (002) TiC//(104)Ti₃SiC₂, and [11ˉ0]TiC//[110]Ti₃SiC₂. Based on the above interfacial relations an interfacial structure model was established. The structure of Ti₃SiC₂ could be considered as two-dimensional closed packed layers of Si periodically intercalated into the (111) twin boundary of TiC_0.67 (Ti₃C₂). The intercalation resulted in the transformation from cubic TiC_0.67 to hexagonal Ti₃SiC₂. In the opposite case, de-intercalation of Si from Ti₃SiC₂ caused the transformation from hexagonal Ti₃SiC₂ to cubic TiC_0.67. Understanding the crystallographic relations between Ti₃SiC₂ and TiC is of vital importance in both understanding the properties and optimizing the processing route for preparing pure Ti₃SiC₂. Received: 10 February 2000 / Reviewed and accepted: 17 March 2000     

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.     

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.     

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.     

In-situ hot pressing/solid-liquid reaction synthesis of dense titanium silicon carbide bulk ceramics

 An in-situ hot pressing/solid-liquid reaction process was developed for the synthesis of dense polycrystalline Ti₃SiC₂ ceramics using Ti, Si, and graphite powders as starting materials. The present work demonstrated that this process was one of the most effective and simple methods for the preparation of dense bulk Ti₃SiC₂ materials. Lattice constants of a=3.068 and c=17.645 are calculated for Ti₃SiC₂ made through this process. The synthesis temperature influenced the phase composition, microstructure and mechanical properties of Ti₃SiC₂ prepared at different temperatures. And bulk materials with flexural strength of 480 MPa and fracture toughness of 7.88 MPa.m^1/2 were obtained at 1600°C. The high fracture toughness and strength are discussed based on microstructure analysis. Received: 31 July 1998 / Accepted: 28 August 1998     

Synergetic lubricating effect of MoS2 and Ti3SiC2 on tribological properties of NiAl matrix self-lubricating composites over a wide temperature range

NiAl matrix self-lubricating composites with MoS₂ and Ti₃SiC₂ lubricants were prepared by spark plasma sintering. The tribological behaviors of the NiAl–Ti₃SiC₂–MoS₂ composites against Si₃N₄ were investigated from room temperature to 800 °C. The results showed that the composites exhibited excellent self-lubricating and anti-wear properties over a wide temperature range. At 400 °C, the composites containing 5Ti₃SiC₂–5MoS₂ (wt.%) had a very low friction coefficient of about 0.13 and a low wear rate of 4.5 × 10⁻⁵ mm³ N⁻¹ m⁻¹. MoS₂ played the main role of lubrication at low temperatures, while Ti₃SiC₂ was responsible for low friction at high temperatures. Ti₃SiC₂ and MoS₂ lubricants in the NiAl–Ti₃SiC₂–MoS₂ composites showed the excellent synergetic lubricating effect over a wide temperature range from room temperature to 800 °C.     

Interactions between Ti and alumina-based ceramics

Reactive metal coatings have been frequently used on ceramic materials for various purposes. However, little work was done in the past to understand the interactions between coating and ceramic substrates and their effects on the mechanical properties of the ceramics. In this study, titanium coatings were applied to single-crystal (sapphire) and polycrystalline alumina to study the interface reactions. Also, the effect of the coating on the mechanical properties of the substrates was quantified in terms of modulus of rupture (MOR) in four-point bending strength. Reactions between the coating and the Al₂O₃-based substrates at 980°C caused the formation of a new phase, Ti₃Al[O], and a significant decrease (15%–65%) in the MOR strength of the ceramic materials. This study showed that in polycrystalline alumina, interactions between titanium and the glassy grain-boundary phase in the ceramic materials were responsible for reduction in the MOR strength, while the effect of thermal expansion mismatch between titanium and the ceramic substrate appeared to be dominant for singlecrystal alumina.     

Preparation and characterization of Al2O3-Ti3SiC2 composites and its functionally graded materials

Alumina/titanium silicon carbide (Al₂O₃-Ti₃SiC₂) composites and its functionally graded materials (FGMs) were fabricated by a powder metallurgy processes and their microstructure and properties were investigated, respectively. The experimental results showed that the Vickers hardness of composites decreased with increasing Ti₃SiC₂ content while the fracture toughness and strength exhibited the opposite trend. Minimum Vickers hardness (4 GPa), maximum strength (598 MPa) and maximum toughness (11.24 MPa m^1/2) were reached in the pure Ti₃SiC₂ material. Strength and hardness of FGMs were evaluated. Observation using an scanning electron microscope (SEM) indicated that the presence of Ti₃SiC₂ of FGMs inhibited the growth of alumina grains through a pinning mechanism. The study shows that the combination of the layered Ti₃SiC₂ structure and the fine alumina grains can result in a Al₂O₃-Ti₃SiC₂ composites possessing a high toughness and low Vickers hardness without a sacrifice in the strength.     

Superhard pcBN tool materials with Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript> MAX-phase binder: Structure,properties, application

Superhard cutting tool materials were sintered in cBN–(Ti₃SiC₂–TiC) system via high pressure–high temperature method. Sintering was performed under the pressure 8 GPa in the 1400–2400°C temperature range. The initial mixtures of three compositions were chosen with 90, 80 and 60 vol % cBN. The mixtures were prepared by mixing cBN (1–3 μm) and Ti₃SiC₂–TiC (< 2 μm). It was found, that upon sintering, the compositions of the obtained samples differed from the initial mixtures in all cases as a result of chemical reactions. Microstructure observations, phase composition estimation, and mechanical properties of the obtained tool materials were carried out. The results indicate that both the varying cBN content and the applied sintering conditions have a direct effect on the structure, properties, and kinetics of reactions.     

Synthesis and some properties of Ti3SiC2 by hot pressing of titanium,silicon, and carbon powders Part 1 – Effect of starting composition on formation of Ti3SiC2 and observation of Ti3SiC2 crystal morphology

Abstract

Dense Ti₃SiC₂ bulk ceramic was synthesised by hot pressing of elemental titanium, silicon, and carbon powders. The effects of starting composition of the powders on the synthesis of pure Ti₃SiC₂ were examined. Phase identification was carried out by X-ray diffraction. Silicon content in the starting composition played an important role in formation of the final constituent phases in the composite. It was difficult to obtain the pure phase Ti₃SiC₂ because other thermodynamically stable reaction products such as TiC, TiSi₂, or Ti₅Si₃ were always present together with Ti₃SiC₂. The microstructure of samples was examined using scanning electron microscopy and transmission electron microscopy. Observations showed that the Ti₃SiC₂ matrix was composed of elongated, platelike, and equiaxial grains. It is suggested that the hexagonal crystal Ti₃SiC₂ exhibits anisotropic grain growth behaviour. The relative growth rates on different planes, therefore, endow Ti₃SiC₂ with several morphologies.