Facile synthesis of Ti3SiC2 powder by high energy ball-milling and vacuum pressureless heat-treating process from Ti–TiC–SiC–Al powder mixtures

In this article, Ti/TiC/SiC/Al powder mixtures with molar ratios of 4:1:2:0.2 were high energy ball-milled, compacted, and heated in vacuum with various schedules, in order to reveal the effects of temperature, soaking time, thickness of the compacts, and carbon content on the purity of the sintered compacts. X-ray diffraction and scanning electron microscopy were employed to investigate the phase purity, particle size and morphology of the synthesized samples. It was found that the Ti₃SiC₂ content nearly reached 100 wt.% on the surface layer of the sintered compacts prepared in the temperature range from 1350 °C to 1400 °C for 1 h. Powder containing 91 wt.% Ti₃SiC₂ was successfully synthesized by heating 6 mm green compacts of 4Ti/1TiC/2SiC/0.2Al at 1380 °C for 1 h in vacuum. The excessive carbon content failed to improve the purity of Ti₃SiC₂ powder. TiC phase was the main impurity in the formation process of Ti₃SiC₂.     

Effect of excess silicon content on the formation of nano-layered Ti3SiC2 ceramic via infiltration of TiC preforms

The aim of this work was to investigate the effect of silicon content on the formation and morphology of Ti₃SiC₂ based composite via infiltration of porous TiC preforms. The gelcasting process was used for fabrication of preforms. It was found that the infiltrated sample at 1500 °C for 90 min from a mixture of 3TiC/1.5Si containing 92 wt.% Ti₃SiC₂. With the increasing of TiC and SiC impurity phases, Vickers hardness was increased to the maximum value of 12.9 GPa in Ti₃SiC₂–39 wt.%TiC composite. Microscopic observations showed that the Ti₃SiC₂ matrix was composed of columnar, platelike and equiaxial grains with respect to silicon content.     

Fabrication of Ti3SiC2 and Ti4SiC3 MAX phase ceramics through reduction of TiO2 with SiC

Ti₃SiC₂ and Ti₄SiC₃ MAX phase ceramics were fabricated through high-temperature vacuum reduction of TiO₂ using SiC as a reductant, followed by hot pressing of the products under 25 MPa of pressure at 1600 °C. It was found that both Ti₃SiC₂ and Ti₄SiC₃ may be obtained in good yields, depending on the annealing time during the reduction step. In addition to MAX phases, the products contained some amounts of TiC. The hot pressing step did not significantly affect the composition of the products, indicating good stability of Ti₃SiC₂ and Ti₄SiC₃ under these conditions. Analysis of the densification behavior of the samples revealed lower ductility in Ti₄SiC₃ compared to Ti₃SiC₂. The samples prepared herein exhibited the flexural strength, fracture toughness and microhardness typical of coarse-grained MAX-phase ceramics.     

Microstructure evolution of Ti3SiC2 powder during high-energy ball milling

Ti₃SiC₂ powder was milled by high-energy ball milling under argon atmosphere and subsequently thermally annealed. The microstructure evolution of Ti₃SiC₂ after milling was investigated. It was found that 200 nm particle size Ti₃SiC₂ powder could be achieved by 9 h milling whereas a longer milling time would induce Ti₃SiC₂ decomposition. After 18 h milling, the particle size gradually decreased to 150 nm and TiC appeared in the XRD pattern. It is suggested that the collision of the milling balls triggered the formation of TiC from the amorphous phase which was generated in the milling process.     

Microstructure and mechanical strength of transient liquid phase bonded Ti3SiC2 joints using Al interlayer

Based on the structure characteristic of Ti₃SiC₂ and the easy formation of Ti₃Si_1−xAl_xC₂ solid solution, a transient liquid phase (TLP) bonding method was used for bonding layered ternary Ti₃SiC₂ ceramic via Al interlayer. Joining was performed at 1100–1500 °C for 120 min under a 5 MPa load in Ar atmosphere. SEM and XRD analyses revealed that Ti₃Si(Al)C₂ solid solution rather than intermetallic compounds formed at the interface. The mechanism of bonding is attributed to aluminum diffusing into the Ti₃SiC₂. The strength of joints was evaluated by three point bending test. The maximum flexural strength reaches a value of 263 ± 16 MPa, which is about 65% of that of Ti₃SiC₂; for the sample prepared under the joining condition of 1500 °C for 120 min under 5 MPa. This flexural strength of the joint is sustained up to 1000 °C.     

High temperature interfacial phase stability of a Mo/Ti3SiC2 laminated composite

A Mo/Ti₃SiC₂ laminated composite is prepared by spark plasma sintering at 1300 °C under a pressure of 50 MPa. Al powder is used as sintering aid to assist the formation of Ti₃SiC₂. The fabricated composites were annealed at 800, 1000 and 1150 °C under vacuum for 5, 10, 20 and 40 h to study the composite's interfacial phase stability at high temperature. Three interfacial layers, namely Mo₂C layer, AlMoSi layer and Ti₅Si₃ solid solution layer are formed during sintering. Experimental results show that the Mo/Ti₃SiC₂ layered composite prepared in this study has good interfacial phase stability up to at least 1000 °C and the growth of the interfacial layer does not show strong dependence on annealing time. However, after being exposed to 1150 °C for 10 h, cracks formed at the interface.     

Improved mechanical properties of Al2O3 ceramic by in-suit generated Ti3SiC2 and TiC via hot pressing sintering

Al₂O₃ multi-phase composites with different volume fractions of SiC varying from 0 vol% to 30.0 vol% were fabricated by vacuum hot pressing sintering at 1600 °C under the pressure of 30 MPa for 2.0 h. The aim of this work was to investigate the effect of SiC content on the morphology and mechanical properties of the Al₂O₃ multi-phase composite. The results show that the addition of SiC and Ti can produce new strengthening and reinforcing phases include Ti₃SiC₂, TiC, Ti₅Si₃, which would hamper the migration of grain boundaries and promote sintering. The mechanical performances could reach the comprehensive optimal values for 20.0 vol% SiC, delamination and transgranular fracture being the major crack propagation energy dissipation mechanisms.     

Machinability of Ti3SiC2 with layered structure synthesized by hot pressing mixture of TiCx and Si powder

Nanolaminate Ti₃SiC₂ was synthesized from a mixture of TiC_x (x = 0.67)/Si powder by hot pressing to increase machinability. Ti₃SiC₂ was synthesized at temperatures of 1360 °C and 1420 °C for 90 min under a pressure of 25 MPa. The X-ray diffraction results showed that while mainly Ti₃SiC₂ with some unreacted TiC_x were detected in the synthesized samples at 1360 °C, no phases except Ti₃SiC₂ phases remained in the synthesized samples at 1420 °C. The cutting resistance of Ti₃SiC₂ was measured in terms of the principle, feed, and thrust forces and was compared with that of middle-carbon steel, SM45C. The values of the principal force of the synthesized Ti₃SiC₂ were lower than those of SM45C. After machining, the roughness of the Ti₃SiC₂ was lower than those of SM45C; however, the damage to the tool bit used for the machining of SM45C was less than the damage to those used for the machining of the Ti₃SiC₂.     

Effects of Xe+ irradiation on Ti3SiC2 at RT and 500 °C

In this study, effects of a 400 keV Xe⁺ irradiation on Ti₃SiC₂ were systematically investigated by transmission electron microscopy (TEM). At RT, results show that the Xe⁺ irradiation induced the dissociation of Ti₃SiC₂ to polycrystalline TiC first, and then the polycrystalline to TiC nanograins with the increasing fluence. However, there is no significant microstructure change observed on the sample irradiated at 500 °C. It is demonstrated that Ti₃SiC₂ had not been completely amorpherized even up to 116.9 displacements per atom (dpa).     

Brazing SiC ceramic using novel B4C reinforced Ag–Cu–Ti composite filler

The development of new composite fillers is crucial for joining ceramics or ceramics to metals because the composite fillers exhibit more advantages than traditional brazing filler metal. In this research, novel B₄C reinforced Ag–Cu–Ti composite filler was developed to braze SiC ceramics. The interfacial microstructure of the joints was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of B₄C addition and brazing temperature on the microstructure evolution and mechanical properties of the joints was analyzed. The results revealed that TiB whisker and TiC particles were simultaneously synthesized in the Ag-based solid solution and Cu-based solid solution due to the addition of B₄C particles. As the brazing temperature increased, the thickness of Ti₃SiC₂+Ti₅Si₃ layers adjacent to SiC ceramic increased. Desirable microstructure similar to the metal matrix reinforced by TiB whisker and TiC particles could be obtained at brazing temperature of 950 °C. The maximum bending strength of 140 MPa was reached when the joints brazed at 950 °C for 10 min, which was 48 MPa (~52%) higher than that of the joints brazed using Ag–Cu–Ti filler.     

Low-temperature synthesis of high-purity Ti3AlC2 by MA-SPS technique

Ternary carbide Ti₃AlC₂ was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS) from elemental powder mixtures of Ti, Al and C, and the effect of Al content on formation of Ti₃AlC₂ during both processes was investigated. The results showed that adding proper Al content in the staring materials significantly increased the phase purity of Ti₃AlC₂ in the synthesized samples. Dense and high-purity Ti₃AlC₂ with <1 wt.% TiC could be successfully obtained by spark plasma sintering of powders mechanically alloyed for 9.5 h from a starting powder mixtures of 3Ti/1.1Al/2C at a lower sintering temperature of 1050 °C for 10–20 min.     

Microstructure and mechanical properties of SiC-SiC joints joined by spark plasma sintering

The development of reliable joining technology is of great importance for the full use of SiC. Ti₃SiC₂, which is used as a filler material for SiC joining, can meet the demands of neutron environment applications and can alleviate residual stress during the joining process. In this work, SiC was joined using different powders (Ti₃SiC₂ and 3Ti/1.2Si/2C/0.2Al) as filler materials and spark plasma sintering (SPS). The influence of the joining temperature on the flexural strength of the SiC joints at room temperature and at high temperatures was investigated. Based on X-ray diffraction and scanning electron microscopy analyses, SiC joints with 3Ti/1.2Si/2C/0.2Al powder as the filler material possess high flexural strengths of 133 MPa and 119 MPa at room temperature and at 1200 °C, respectively. The superior flexural strength of the SiC joint at 1200 °C is attributed to the phase transformation of TiO₂ from anatase to rutile.     

Hot corrosion behavior of Ti3SiC2 in the mixture of Na2SO4–NaCl melts

The corrosion behavior of polycrystalline Ti₃SiC₂ was studied in the mixture of Na₂SO₄–NaCl melts with various mass ratios at 850 °C. The results demonstrated that Ti₃SiC₂ suffered from serious hot corrosion attack in the mixture of Na₂SO₄–NaCl melts when the concentration of Na₂SO₄ was higher than 35 wt.%. A large amount of corrosion products spalled from specimens during the tests and obvious mass loss was observed. Hot corrosion of Ti₃SiC₂ would become severe because NaCl had lower melting-point and caused Na₂SO₄–NaCl mixture melted below 850 °C. However, when the concentration of Na₂SO₄ was lower than 25 wt.% in the mixture, a protective oxide layer (SiO₂ + TiO₂) formed on the substrate, the corrosion rate of Ti₃SiC₂ became quite slow and slight mass gain was observed, the corrosion products did not spall from substrate at 850 °C. The microstructure and phase composition of the corroded samples were investigated by SEM/EDS and XRD.     

Ti3Si(Al)C2-based ceramics fabricated by reactive melt infiltration with Al70Si30 alloy

Dense Ti₃Si(Al)C₂-based ceramics were synthesized using reactive melt infiltration (RMI) of Al₇₀Si₃₀ alloy into the porous TiC preforms. The effects of the infiltration temperature on the microstructure and mechanical properties of the synthesized composites were investigated. All the composites infiltrated at different temperatures were composed of Ti₃Si(Al)C₂, TiC, SiC, Ti(Al, Si)₃ and Al. With the increase of infiltration temperature from 1050 °C to 1500 °C, the Ti₃Si(Al)C₂ content increased to 52 vol.% and the TiC content decreased to 15 vol.%, and the Vickers hardness, flexural strength and fracture toughness of Ti₃Si(Al)C₂-based composite reached to 9.95 GPa, 328 MPa and 4.8 MPa m^1/2, respectively.     

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.     

High temperature properties of the monolithic CVD β-SiC materials joined with a pre-sintered MAX phase Ti3SiC2 interlayer via solid-state diffusion bonding

Monolithic high purity CVD β-SiC materials were successfully joined with a pre-sintered Ti₃SiC₂ foil via solid-state diffusion bonding. The initial bending strength of the joints (∼ 220 MPa) did not deteriorate at 1000 °C in vacuum, and the joints retained ∼ 68 % of their initial strength at 1200 °C. Damage accumulation in the interlayer and some plastic deformation of the large Ti₃SiC₂ grains were found after testing. The activation energy of the creep deformation in the temperature range of 1000 – 1200 °C in vacuum was ∼ 521 kJmol⁻¹. During the creep, the linkage of a significant number of microcracks to form a major crack was observed in the interlayer. The Ti₃SiC₂ interlayer did not decompose up to 1300 °C in vacuum. A mild and well-localized decomposition of Ti₃SiC₂ to TiC_x was found on the top surface of the interlayer after the bending test at 1400 °C in vacuum, while the inner part remained intact.     

Sintering,mechanical, electrical and oxidation properties of ceramic intermetallic TiC–Ti3Al composites obtained from nano-TiC particles

The paper discusses the development of a new material system for interconnect application in Solid Oxide Fuel Cells (SOFC) based on TiC–Ti₃Al. Nano-sized TiC powders utilized in this research were synthesized using carbon coated TiO₂ precursors from a patented process. The pressureless sintering of TiC–Ti₃Al in a vacuum was applied at temperatures between 1100 °C and 1500 °C and content of Ti₃Al was varied in the range of 10–40 wt%. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used for phase evaluation and sintering behavior. Relative density increased markedly with increasing sintering temperature because of grain growth and formation of the Ti₃AlC₂ secondary phase. Dense products (>95% TD) were prepared from nanosized TiC powders with 10 and 20 wt% Ti₃Al, but with about 8 to 10% porosity for 30 and 40 wt% Ti₃Al. The mechanical properties were determined from Vickers hardness and fracture toughness calculations. Vickers hardness decreased and fracture toughness increased with increasing Ti₃Al content. The electrical conductivity and oxidation behavior of TiC–Ti₃Al composites were investigated to evaluate the feasibility for SOFC interconnect application. The electrical conductivity measurements in the air at 800 °C for 100 h were made using the Kelvin 4-wire method.     

Influence of mechanical alloying on Ti3SiC2 formation via spark plasma sintering technique from Ti/SiC/C powders

Ti₃SiC₂ was elaborated by two different methods: (i) Spark plasma sintering of 5Ti/2SiC/C powders and (ii) mechanical alloying of powders followed by Spark plasma sintering. The results showed that mechanical alloying was not advantageous for pure Ti₃SiC₂ formation but it can significantly improve the density of the obtained bulk material via the particles refinement as well as the microhardness by increasing the TiC content. It was found that the relative density was increased up to 98.58% for the sintered mechanically alloyed sample whereas it was not more than 96.04% for the sintered 5Ti/2SiC/C starting powders. The Vickers microhardness measured for both bulk samples demonstrates a high improvement for the previously mechanically alloyed powder mixture, as it was of about 1282 Hv and only 581.2 Hv for the alloy obtained from 5Ti/2SiC/C starting powders.     

Thickness-dependent phase evolution and bonding strength of SiC ceramics joints with active Ti interlayer

A robust solid state diffusion joining technique for SiC ceramics was designed with a thickness-controlled Ti interlayer formed by physical vapor deposition and joined by electric field-assisted sintering technology. The interface reaction and phase revolution process were investigated in terms of the equilibrium phase diagram and the concentration-dependent potential diagram of the Ti-Si-C ternary system. Interestingly, under the same joining conditions (fixed temperature and annealing duration), the thickness of the Ti interlayer determined the concentration and distribution of the Si and C reactants in the resulting joint layer, and the respective diffusion distance of Si and C into the Ti interlayer differentiated dramatically during the short joining process (only 5 min). In the case of a 100 nm Ti coating as an interlayer, the C concentration in the joint layer was saturated quickly, which benefited the formation of a TiC phase and subsequent Ti₃SiC₂ phase. The SiC ceramics were successfully joined at a low temperature of 1000 °C with a flexural strength of 168.2 MPa, which satisfies applications in corrosive environments. When the Ti thickness was increased to 1 μm, Si atoms diffused easily through the diluted Ti-C alloy (a dense TiC phase was not formed), and the Ti₅Si₃ brittle phase formed preferentially. These findings highlight the importance of the diffusion kinetics of the reactants on the final composition in the solid state reaction, particularly in the joining technique for covalent SiC ceramics.     

Phase reactions in a hot pressed TiC/Si powder mixture

This work investigated the possibility of producing dense Ti₃SiC₂ by hot pressing TiC/Si powders. A hot press with graphite heating elements was used for densification and the phase reactions of some hot pressed samples were further evaluated by pressureless heating in a dilatometer. The density and phase composition of the heat treated samples were evaluated using Archimedes principle and by X-ray diffractometry, respectively. Hot pressing resulted in a low Ti₃SiC₂ yield; the main phases were TiC and TiSi₂ regardless of starting powder composition, temperature, holding time or pressure. A second heating without pressure resulted in Ti₃SiC₂ formation, but only in samples initially hot pressed at 1300 °C or lower. At higher hot pressing temperatures, thin oxide layers on particle surfaces were locked into the structure. Acting as diffusion barriers, they prevented the Ti₃SiC₂ forming reaction. In hot pressed samples the density was significantly higher than in samples sintered without pressure.