Interface structure and wetting behaviour of Cu/Ti3SiC2 system

Wetting behaviour of a Cu/Ti₃SiC₂ system was investigated by the sessile drop technique under a vacuum atmosphere. Contact angles between Cu and Ti₃SiC₂ changed from 95 to 15° as temperatures increased from 1089 to 1270°C. Two distinct reaction layers consisting of different contents of Cu, TiC_x, Ti₃SiC₂ and Cu_xSi_y intermetallics were formed at the interface of Cu and Ti₃SiC₂. The formation of the interface layers contributes to the improvement of the wettability of the system. The dissolution of Si from theTi₃SiC₂ into the molten Cu at high temperature plays a dominant role in the wetting behaviour of Cu/Ti₃SiC₂ systems.     

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.     

In situ synthesis,mechanical and cyclic oxidation properties of Ti3AlC2/Al2O3 composites

ABSTRACT

Ti₃AlC₂/Al₂O₃ composite materials were successfully fabricated from TiO₂/TiC/Ti/Al powders by the in situ reactive hot pressed technique. The microstructure, mechanical and oxidation properties of the composites were investigated in the paper. Vickers hardness increased with the Al₂O₃ content. The relative density of Ti₃AlC₂/Al₂O₃ composites exhibits a declining tendency with Al₂O₃ content especially exceeds 10 vol.?%. The Ti₃AlC₂/Al₂O₃ composites show excellent electrical conductivity. The flexural strength and fracture toughness of Ti₃AlC₂/10 vol. % Al₂O₃ are 461 ± 20?MPa and 6.2?±?0.2?MPa m^1/2, respectively. The cyclic oxidation behaviour of resistance of Ti₃AlC₂/10 vol. % Al₂O₃ composites at 800–1000°C generally obeys a parabolic law. The oxide scale of sample consists of a mass of α-Al₂O₃ and TiO₂, forming a dense and adhesive protect layer. The result indicates that the Al₂O₃ can greatly improve the oxidation resistance of Ti₃AlC₂.     

Reaction mechanism in Ti–SiC–C powder mixture during pulse discharge sintering

During pulse discharge sintering (PDS) of Ti/SiC/C powder mixture, combustion synthesis reactions occurred at heating rates above 20 °C/min. With an increase in heating rate, combustion synthesis occurred at higher temperatures. The essential of this combustion reaction is the liquid reaction between Ti and formed Ti₅Si₃. The exothermic TiC formation during PDS process promotes this liquid reaction. We have found that the combustion reactions alone did not finish the formation reactions for Ti₃SiC₂, and further heating following the combustion reactions is necessary for the synthesis process of Ti₃SiC₂.     

In situ preparation of SiC/Si3N4-NW composite powders by combustion synthesis

Large-scale composite powders containing silicon carbide (SiC) particles and silicon nitride nanowires (Si₃N₄-NWs) were synthesized in situ by combustion synthesis (CS). In this process, a mixture of silicon, carbon black, polytetrafluoroethylene (PTFE) and a small amount of iron powders was used as the precursor. The products were characterized by XRD, SEM, EDS and TEM. The particles are equiaxed with diameters in the micron range, and the in situ formed nanowires are straight with uniform diameters of 20-350 nm and lengths of tens of microns. The Si₃N₄-NWs are characterized to be α-phase single crystals grown along the [1 0 1] or [1 0 0] direction. VLS and SLGS processes are proposed as the growth mechanisms of the nanowires. The as-synthesized powders have great potential for use in the preparation of high-performance SiC/Si₃N₄-NW composites.     

Microstructure and mechanical properties of in situ synthesized (TiB2 + TiC)/Ti3SiC2 composites

Based on thermodynamic analysis, highly dense (TiB₂ + TiC)/Ti₃SiC₂ composite ceramics with different TiB₂ volume contents were in situ fabricated in situ by hot-pressing at 1500 °C. Laminar Ti₃SiC₂ grains, columnar TiB₂ grains and equiaxed TiC grains were clearly identified from microstructural observation; grain boundaries were clean. The increase of TiB₂ volume content significantly restrains the grain growth of the Ti₃SiC₂ matrix. As the content of TiB₂ increases from 5 vol.% to 20 vol.%, the bending strength and fracture toughness of the composites both increase and then decrease, whereas the Vickers hardness increases linearly from 6.13 GPa to 11.5 GPa. The composite with 10 vol.% TiB₂ shows the optimized microstructure and optimal mechanical properties: 700 MPa for bending strength; 9.55 MPa m^1/2 for fracture toughness. These are attributed to the synergistic action of strengthening and toughening mechanisms such as particulate reinforcement, crack deflection, grain's pull-out and fine-grain toughening, caused by the columnar TiB₂ grains and equiaxed TiC grains.     

Solution combustion synthesis and physicochemical characterization of ZrO2-MoO3 nanocomposite oxides prepared using different fuels

A series of MoO₃-ZrO₂ nanocomposite oxides with MoO₃ content in the range of 2-20 mol% were prepared by solution combustion method. Three different fuels namely urea, glycine and hexamethylenetetramine (HMTA) were used for the preparation of MoO₃-ZrO₂ oxides. For the sake of comparison, the MoO₃-ZrO₂ composite oxides were also prepared by impregnation of zirconia with molybdenum salt precursor and subsequent heat treatment. The synthesized nanomaterials were characterized by XRD, SEM, TEM and UV-vis spectroscopic technique. XRD study indicated selective stabilization of the tetragonal phase of zirconia in the presence of MoO₃. The method of preparation was found to be crucial for the phase composition of zirconia in the composite oxide. The crystallite size and rms stain were calculated from the Fourier line shape analysis of the broadened X-ray diffraction profiles. With increase in the MoO₃ content, the crystallite size of the tetragonal zirconia phase was found to be decreased. TEM study indicated the presence of small nanoparticles with size in the 5-10 nm range. UV-vis study of the composite oxide materials revealed well dispersion of the molybdenum oxide component in the form of monomer, dimers and nanoclusters in the zirconia matrix. The nature of fuel was found to be crucial in determining the morphology and shape of the particles.     

Preparation of SiC reinforced Ti3SiC2-base composite and its biocompatibility evaluation

Soft Ti₃SiC₂ ceramic is a new class of potential biomaterial for orthopaedic applications and dental implants. Introducing SiC into Ti₃SiC₂ can compensate for the relatively low hardness of the Ti₃SiC₂ implants. In this study, SiC reinforced Ti₃SiC₂-base composites were fabricated by reactive sintering of powder compacts. Mechanical properties and phase constitution of the prepared samples were studied. Biocompatibility of the composite was evaluated by implanting the material onto the shaft surface of the femur of a rabbit, while, biostability was studied by immersing the material into human blood plasma and also into a simulated body fluid (Hank's) for prolonged time.     

Combustion synthesis of porous TiC/Ni composites under high gravity

Abstract

Porous TiC/Ni composites were prepared by combustion synthesis under high gravity. In TiC/Ni composites, hollow spheres of 50–200 μm were produced, and their walls were composed of large TiC grains and small Ni particles. A larger average size of the spheres was observed in the samples prepared under high gravity compared with those obtained under normal gravity. Phase segregation was observed under high gravity, and Ni was enriched in the lower part of the samples. It is proposed that the mobility and collision frequency of liquid droplets will increase, and thus, the agglomeration of primary droplets can be enhanced under high gravity.     

Fuel mixture approach for solution combustion synthesis of Ca3Al2O6 powders

Single-phase 3CaO·Al₂O₃ powders were prepared via solution combustion synthesis using a fuel mixture of urea and β-alanine. The concept of using this fuel mixture comes from the individual reactivity of calcium nitrate and aluminum nitrate with respect to urea and β-alanine. It was proved that urea is the optimum fuel for Al(NO₃)₃ whereas β-alanine is the most suitable fuel for Ca(NO₃)₂. X-ray diffraction and thermal analysis investigations revealed that heating at 300 °C the precursor mixture containing the desired metal nitrates, urea and β-alanine triggers a vigorous combustion reaction, which yields single-phase nanocrystalline 3CaO·Al₂O₃ powder (33.3 nm). In this case additional annealing was no longer required. The use of a single fuel failed to ensure the formation of 3CaO·Al₂O₃ directly from the combustion reaction. After annealing at 900 °C for 1 h, the powders obtained by using a single fuel (urea or β-alanine) developed a phase composition comprising of 3CaO·Al₂O₃, 12CaO·7Al₂O₃ and CaO.     

The influence of mechanochemical activation on combustion synthesis of Si3N4

This study addresses itself in the performance of Si₃N₄ combustion synthesis, occurred in the presence of Si₃N₄ and NH₄Cl powders in N₂ atmosphere of 6 MPa. Mechanochemical activation of Si powder, achieved via high-energy attrition milling up to 24 h, increases the intensity and the efficiency of the reactions between Si and N₂ as well as combustion temperature. Benign processing conditions, anticipated with lower mechanochemical activation of Si powder, low N₂ pressures, and low combustion temperatures, favor formation of α-Si₃N₄.     

Preparation and tribological behaviour of laminated Ti3AlC2 crystals as additive in base oil

Abstract

Laminated ternary compound Ti₃AlC₂ crystals were synthesised by pressureless sintering the mixture powders of 3Ti/1·1Al/1·8C, 3Ti/1Al/1·8C/0·2Sn, 1Ti/1·8TiC/1Al and 1Ti1·8TiC1Al0·1Sn at 1400°C with preliminary liquid magnetic stirring mixing. The X-ray diffraction results indicate that Ti₃AlC₂ prepared from 3Ti/1Al/1·8C/0·2Sn has the highest purity, and the addition of appropriate Sn favours the synthesis of high purity Ti₃AlC₂. Scanning electron microscopy images show that Ti₃AlC₂ samples exhibit lamellar-like microstructure with thickness of ～100 nm. The tribological properties of Ti₃AlC₂ as an additive in 100SN base oil were evaluated with a ball on disc tester. The results show that the Ti₃AlC₂ additives exhibited good friction reduction and wear resistance at 5 wt-% concentration. Under determinate conditions, the base oil containing 5 wt-% Ti₃AlC₂ samples presented good tribology performance under the load of 15 N. The improved tribological properties of the Ti₃AlC₂ samples could be attributed to the formation of tribofilm in friction process.     

Material removal and surface damage in EDM of Ti3SiC2 ceramic

Material removal and surface damage of Ti₃SiC₂ ceramic during electrical discharge machining (EDM) were investigated. Melting and decomposition were found to be the main material removal mechanisms during the machining process. Material removal rate was enhanced acceleratively with increasing discharge current, i_e, working voltage, u_i, but increased deceleratively with pulse duration, t_e. Microcracks in the surface and loose grains in the subsurface resulted from thermal shock were confirmed, and the surface damage in Ti₃SiC₂ ceramic led to a degradation of both strength and reliability.     

Synthesis and photocatalytic properties of H2La2Ti3O10/TiO2 intercalated nanomaterial

H₂La₂Ti₃O₁₀/ TiO₂ intercalated nanomaterial was fabricated by successive intercalation reactions of H₂La₂Ti₃O₁₀ with n-C₆H₁₃NH₂/C₂H₅OH mixed solution and acid TiO₂ sol, followed by irradiating with a high-pressure mercury lamp. The intercalated materials possess a gallery height of 0.46 nm and a specific surface area of 31.58 m²·g⁻¹, which indicate the formation of a porous material. H₂La₂Ti₃O₁₀/TiO₂ shows photocatalytic activity for the decomposition of organic dye under irradiation with visible light and the activity of TiO₂ intercalated material was superior to the unsupported one.     

Microstructure and mechanical properties of Zn based composites reinforced by Ti3AlC2

30?vol.-% Ti₃AlC₂ particle reinforced Zn based (Zn–27?wt-% Al, denoted as ZA27) composites have been prepared via three different mechanically activated sintering technologies: pressureless sintering, hot pressing and combination of pressureless sintering and hot pressing (two-step sintering) technology. The relationship between sintering conditions, microstructure and mechanical properties of the 30?vol.-% Ti₃AlC₂/ZA27 composites has been investigated. The Ti₃AlC₂/ZA27 composite with enhanced tensile strength of 335?MPa and bending strength of 570?MPa was achieved by the two-step technology. The improved mechanical properties are attributed to the good bonding between reinforcing particles and matrix as well as the fine grained microstructure. Raising the sintering temperature is more efficient to improve the mechanical properties of the composites than applying pressure.     

Effect of Ti5Si3 on wear properties of Ti3Si(Al)C2

Near-fully dense Ti₃Si(Al)C₂/Ti₅Si₃ composites were synthesized by in situ hot pressing/solid–liquid reaction process under a pressure of 30 MPa in a flowing Ar atmosphere at 1580 °C for 60 min. Compared to monolithic Ti₃Si(Al)C₂, Ti₃Si(Al)C₂/Ti₅Si₃ composites exhibit higher hardness and improved wear resistance, but a slight loss in flexural strength (about 26% lower than Ti₃Si(Al)C₂ matrix). In addition, Ti₃Si(Al)C₂/Ti₅Si₃ composites maintain a high fracture toughness (K_IC = 5.69–6.79 MPa m^1/2). The Ti₃Si(Al)C₂/30 vol.%Ti₅Si₃ composite shows the highest Vickers hardness (68% higher than that of Ti₃Si(Al)C₂) and best wear resistance (the wear resistance increases by 2 orders of magnitude). The improved properties are mainly ascribed to the contribution of hard Ti₅Si₃ particles, and the strength degradation is mainly due to the lower Young's modulus and strength of Ti₅Si₃.     

Rapid and low temperature synthesis of high purity Ti2SC powder by microwave hybrid heating

Ti₂SC powders were successfully synthesised at relatively low temperature by a microwave hybrid heating method. The mixtures of Ti, C and S or TiS₂ with different molar ratios were heated to investigate the formation of Ti₂SC phase. It was confirmed that Ti₂SC with high purity was achieved using TiS₂ as sulphur source. The results indicated that the synthesis temperature of Ti₂SC was ～500°C lower, and holding time was only one-twentieth compared with those reported by other methods. The high purity Ti₂SC powders from Ti/TiS₂/C with the molar ratio of 2.85:1.15:2 obtained at 1100°C for 3?min were uniform, and the average particle size was 1–2?μm.     

Hydrothermal synthesis of flaky crystallized La2Ti2O7 for producing hydrogen from photocatalytic water splitting

Flaky monoclinic La₂Ti₂O₇ was prepared via a hydrothermal method based on the reaction of Ti(SO₄)₂ and La(NO₃)₃. Relative to the solid-state reaction sample, the flaky La₂Ti₂O₇ showed higher surface areas, much smaller crystal size and more efficient light absorption. All these factors led to the higher photoactivity to produce H₂ from water splitting under UV irradiation.     

Oxidation behavior and kinetics of in situ (TiB2 + TiC)/Ti3SiC2 composites in air

The isothermal oxidation behavior of in situ (TiB₂ + TiC)/Ti₃SiC₂ composite ceramics with different TiB₂ content has been investigated at 900-1200 °C in air for exposure times up to 20 h by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The oxidation of (TiB₂ + TiC)/Ti₃SiC₂ composites follows a parabolic rate law. With the increase in TiB₂ content, the oxidation weight gain, thickness of the oxidation scale, and parabolic rate constant decrease dramatically, which suggests that the incorporation of TiB₂ greatly improves the oxidation resistance of the composites. With the increase in oxidation temperature, the enhancement effect becomes more pronounced. Due to the incorporation of TiB₂, the oxidation scale of (TiB₂ + TiC)/Ti₃SiC₂ composites is generally composed of an outer layer of coarse-grained TiO₂ and an inner layer of amorphous boron silicate and fine-grained TiO₂. Only the dense inner layer formed on the surface acts as a diffusion barrier, retarding the inward diffusion of O, and consequently contributing to the improved oxidation resistance of the (TiB₂ + TiC)/Ti₃SiC₂ composites.     

Growth and characterization of TiO2 nanotubes from sputtered Ti film on Si substrate

In this paper, we present the synthesis of self-organized TiO₂ nanotube arrays formed by anodization of thin Ti film deposited on Si wafers by direct current (D.C.) sputtering. Organic electrolyte was used to demonstrate the growth of stable nanotubes at room temperature with voltages varying from 10 to 60 V (D.C.). The tubes were about 1.4 times longer than the thickness of the sputtered Ti film, showing little undesired dissolution of the metal in the electrolyte during anodization. By varying the thickness of the deposited Ti film, the length of the nanotubes could be controlled precisely irrespective of longer anodization time and/or anodization voltage. Scanning electron microscopy, atomic force microscopy, diffuse-reflectance UV–vis spectroscopy, and X-ray diffraction were used to characterize the thin film nanotubes. The tubes exhibited good adhesion to the wafer and did not peel off after annealing in air at 350 °C to form anatase TiO₂. With TiO₂ nanotubes on planar/stable Si substrates, one can envision their integration with the current micro-fabrication technique large-scale fabrication of TiO₂ nanotube-based devices.