Effect of TiO2 addition on the properties of Ti3Si(Al)C2 based ceramics fabricated by reactive melt infiltration

In this paper, Ti₃Si(Al)C₂ based ceramics were fabricated by reactive melt infiltration (RMI) of TiC/TiO₂ preforms with liquid silicon. The microstructure, phase composition, and mechanical properties of the Ti₃Si(Al)C₂ based ceramics have been investigated to understand the effect of phase composition of the preforms on the formation mechanisms of Ti₃Si(Al)C₂. The preforms with different content of TiO₂ infiltrated at 1500 °C with liquid silicon for 1 h were composed of Ti₃Si(Al)C₂, Al₂O₃, TiC, TiSi_xAl_y and residual Al. The prior generated Al₂O₃ phases inhibited the dispersion of Ti₃Si(Al)C₂ phases, resulting in the drastically grain growth of Ti₃Si(Al)C₂. Subsequently, the microstructure with gradually increasing Ti₃Si(Al)C₂ grain size resulted in the decrease of the bending strength and fracture toughness of samples. When the content of TiO₂ reached 20 wt%, the bending strength reached the maximum, 326.6 MPa. The fracture toughness attained the maximum, 4.3 MPa m^1/2, when the content of TiO₂ was 10 wt%.     

A dense and fine-grained SiC/Ti3Si(Al)C2 composite and its high-temperature oxidation behavior

A dense SiC/Ti₃Si(Al)C₂ composite was synthesized by in situ hot pressing powders of Si, TiC and Al as a sintering additive at 1500 °C for 2 h under 30 MPa in Ar atmosphere. This composite has a fine-grained and homogeneous microstructure with grain sizes of 5 μm for Ti₃Si(Al)C₂ and of 1 μm for SiC. The SiC/Ti₃Si(Al)C₂ composite possesses an improved oxidation resistance, with parabolic rate constants of 4.57 × 10^?8 kg²/m⁴/s at 1200 °C and 1.31 × 10^?7 kg²/m⁴/s at 1300 °C. This study provides an experimental evidence to confirm the formation of amorphous phases in the oxide scale of the SiC/Ti₃Si(Al)C₂ composite. Microstructure and phase composition of the SiC/Ti₃Si(Al)C₂ composite and oxide scales were identified by X-ray diffractometry and scanning electron microscopy. The mechanism for the enhanced oxidation resistance has been discussed.     

Fabrication and electromagnetic interference shielding effectiveness of Ti3Si(Al)C2 modified Al2O3/SiC composites

A dense alumina fiber reinforced silicon carbide matrix composites (Al₂O₃/SiC) modified with Ti₃Si(Al)C₂ were prepared by a joint process of chemical vapor infiltration, slurry infiltration and reactive melt infiltration. The conductive Ti₃Si(Al)C₂ phase introduced into the matrix modified the microstructure of Al₂O₃/SiC. The refined microstructure was composed of conductive phase, semiconductive phase and insulating phase, which led to admirable electromagnetic shielding properties. Electromagnetic interference shielding effectiveness (EMI SE) of Al₂O₃/SiC and Ti₃Si(Al)C₂ modified Al₂O₃/SiC were investigated over the frequency range of 8.2–12.4 GHz. The EMI SE of Al₂O₃/SiC-Ti₃Si(Al)C₂ exhibited a significant increase from 27.6 to 42.1 dB compared with that of Al₂O₃/SiC. The reflection and absorption shielding effectiveness increased simultaneously with the increase of the electrical conductivity.     

Preceramic paper-derived Ti3Al(Si)C2-based composites obtained by spark plasma sintering

The paper describes the structure and properties of preceramic paper-derived Ti₃Al(Si)C₂-based composites fabricated by spark plasma sintering. The effect of sintering temperature and pressure on microstructure and mechanical properties of the composites was studied. The microstructure and phase composition were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. It was found that at 1150 °C the sintering of materials with the MAX-phase content above 84 vol% leads to nearly dense composites. The partial decomposition of the Ti₃Al(Si)C₂ phase becomes stronger with the temperature increase from 1150 to 1350 °C. In this case, composite materials with more than 20 vol% of TiC were obtained. The paper-derived Ti₃Al(Si)C₂-based composites with the flexural strength > 900 MPa and fracture toughness of >5 MPa m^1/2 were sintered at 1150 °C. The high values of flexural strength were attributed to fine microstructure and strengthening effect by secondary TiC and Al₂O₃ phases. The flexural strength and fracture toughness decrease with increase of the sintering temperature that is caused by phase composition and porosity of the composites. The hardness of composites increases from ~9.7 GPa (at 1150 °C) to ~11.2 GPa (at 1350 °C) due to higher content of TiC and Al₂O₃ phases.     

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.     

Microstructure,mechanical, thermal,and oxidation properties of a Zr2[Al(Si)]4C5–SiC composite prepared by in situ reaction/hot-pressing

The microstructure, mechanical and thermal properties, as well as oxidation behavior, of in situ hot-pressed Zr₂[Al(Si)]₄C₅–30 vol.% SiC composite have been characterized. The microstructure is composed of elongated Zr₂[Al(Si)]₄C₅ grains and embedded SiC particles. The composite shows superior hardness (Vickers hardness of 16.4 GPa), stiffness (Young's modulus of 386 GPa), strength (bending strength of 353 MPa), and toughness (fracture toughness of 6.62 MPa m^1/2) compared to a monolithic Zr₂[Al(Si)]₄C₅ ceramic. Stiffness is maintained up to 1600 °C (323 GPa) due to clean grain boundaries with no glassy phase. The composite also exhibits higher specific heat capacity and thermal conductivity as well as better oxidation resistance compared to Zr₂[Al(Si)]₄C₅.     

Microstructure and properties of dense Tyranno-ZMI SiC/SiC containing Ti3Si(Al)C2 with plastic deformation toughening mechanism

In this paper, Ti₃Si(Al)C₂ was introduced into dense SiC/SiC to improve the mechanical and electromagnetic interference (EMI) shielding properties. In order to reveal the effect of Ti₃Si(Al)C₂, dense SiC/SiC-Ti₃Si(Al)C₂ and dense SiC/SiC without Ti₃Si(Al)C₂ were fabricated. Owing to the plastic deformation toughening mechanism of Ti₃Si(Al)C₂, SiC/SiC-Ti₃Si(Al)C₂ performs a new damage mode characterized by matrix/matrix (m/m) debonding. High interfacial shear strength (IFSS) due to large thermal residual stress (TRS) is weakened by m/m debonding. This new mode also brings high effective volume fraction of loading fibers and long path of crack propagation. Hence SiC/SiC-Ti₃Si(Al)C₂ exhibits higher flexural strength (503 MPa) and fracture toughness (23.7 MPa · m^1/2) than the dense SiC/SiC without Ti₃Si(Al)C₂. In addition, dense SiC/SiC-Ti₃Si(Al)C₂ shows excellent electromagnetic interference shielding effectiveness (EMI SE, 43.0 dB) in X-band, revealing great potential as thermo-structural and functional material.     

The phase transformation and microstructure of TiAl/Ti2AlC composites caused by hot pressing

Two series of raw materials were adopted to form TiAl/Ti₂AlC composites: Ti/Al/TiC and Ti/Al/C. Differential thermal analysis (DTA) of starting powers and X-ray diffraction (XRD) of samples sintered at different temperatures from 600 °C to 1300 °C by hot pressing were utilized to analyze the phase transformation and the mechanism of synthesis. Scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) was utilized to investigate the morphology characteristics of the products. The experimental results showed that Ti reacted with Al to form TiAl intermetallics below 900 °C; and above 900 °C, TiAl reacted with TiC to produce dense TiAl/Ti₂AlC composites. The products sintered at 1200 °C had fine crystals and dense fibres, and the distribution of Ti₂AlC particles in TiAl matrix was homogeneous.     

Dependence of the microstructure and properties of TiC/Ti3SiC2 composites on extra C addition

TiC/Ti₃SiC₂ composites were synthesized with Ti/Si/C and Al (in which extra C addition ranges from 0 to 25 wt.%) as starting powders by hot-pressed sintering method at 1400 °C under 30 MPa. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to evaluate the phase composition and the fracture surface. The results reveal that with the increase of extra C addition, the content of Ti₃SiC₂ phase decreases while the content of TiC phase increases. Graphite phase is detected in the samples with extra C addition of 20 wt.% and 25 wt.%. The bending strength decreases from 554.81 MPa to 57.44 MPa due to the decrease of the densification and Ti₃SiC₂ phase content. The electrical conductivity falls from 42,474.52 s/cm to 1524.95 s/cm, resulting from lower Ti₃SiC₂ phase content and higher contact resistance.     

Effect of Al2O3 on the microstructure and mechanical properties of Ti3AlC2/Al2O3 in situ composites synthesized by reactive hot pressing

Ti₃AlC₂/Al₂O₃ in situ composites with different Al₂O₃ contents were successfully synthesized from the powder mixture of Ti, TiC, Al and TiO₂ by a reactive hot-pressing method at 1350 °C. The effect of Al₂O₃ on the microstructure and mechanical properties of the composites was investigated in detail. The results indicate that the as-fabricated products mainly consist of Ti₃AlC₂, Al₂O₃ and a small amount of TiC. With increasing the Al₂O₃ content, the flexural strength of Ti₃AlC₂/Al₂O₃ composites increase gradually, the fracture toughness reaches the peak value of 8.21 MPa m^1/2 as the Al₂O₃ content increasing to 9 wt%, the hardness attains the maximum value of 10.16 GPa for 12 wt% Al₂O_3. The strengthening mechanism of the composites was also discussed.     

Reaction synthesis of layered ternary Ti2AlC ceramic

Reactive sintering of 8Ti:Al₄C₃:C powder mixtures to form the ternary carbide Ti₂AlC is studied in the temperature range 570–1400 °C. After sintering at 1400 °C for 1 h, only the MAX phase Ti₂AlC and some TiC are produced. A series of intermediate phases, such as TiC, Ti₃Al, Ti₃AlC are detected during the reactive sintering process. From X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations, a reaction path is proposed for the intermediate phases and Ti₂AlC formation. Results show that reaction kinetics may play an important role in the understanding of the reaction mechanisms.     

High compressive strength in nacre-inspired Al−7Si−5Cu/Al2O3–ZrO2 composites at room and elevated temperatures by regulating interfacial reaction

Al−7Si−5Cu/Al₂O₃−ZrO₂ composites with nacre-like structures were prepared via ice-templating and gas pressure infiltration techniques. The composites were subsequently heat-treated at 850 °C for 0, 30, 60, 90 and 120 min to regulate the interfacial reaction between Al and ZrO₂. The yield of larger (Al_1−m, Si_m)₃Zr and ZrSi₂ phases increased with longer dwell times. The compressive strength initially increased and then decreased. The highest strength was observed in composites treated for 60 min and reached 1600±40, 1261±30 and 1033±22 MPa at temperatures of 20, 150 and 300 °C, respectively. These values increased by 30−40% as compared to those of the non-treated counterparts and were 2-, 5- and 12-fold more than those of the matrix alloy, respectively, which is demonstrative of the material's excellent load-bearing capacity, particularly at elevated temperatures.     

Al alloy/Ti3SiC2 composites fabricated by pressureless infiltration with melt-spun Al alloy ribbons

Al alloy/Ti₃SiC₂ composites with compressive strengths ranging from 743 to 932 MPa have been successfully fabricated by a new two-step pressureless infiltration method. 6061 Al alloy ribbons prepared by melt spinning were employed as the Al alloy matrix for melt infiltration. Shifts in phase constitution and reaction mechanisms of Ti₃SiC₂ preforms in molten Al at 950 °C were investigated, and the compression performance of Al alloy/Ti₃SiC₂ composites was tested. The Vickers hardness of the composites was enhanced to a maximum of 751 HV by increasing the Al content.     

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.     

Developing high toughness and strength Al/TiC composites using ice-templating and pressure infiltration

We prepared Al/TiC composites with different ceramic volume fractions (15, 25 and 35 vol%) using ice-templating and pressure infiltration. The thickness of the lamellar layer and the porosity in the ceramic layer of the TiC scaffolds were controlled by varying the slurry concentration. The Al/15 vol%TiC composite had a thick metal layer and a low-density ceramic layer, which effectively dissipated the stress at the crack tip and fractured in a multiple-crack-propagation mode, giving bending strength of 355±3 MPa and fracture toughness of 81±2 MPa m^1/2. However, the Al/25 vol%TiC and Al/35 vol%TiC composites had much higher bending strength (417−500 MPa) but lower fracture toughness (46−33 MPa m^1/2) as compared to the Al/15 vol%TiC composite, and they fractured in a single-crack-propagation mode. In addition, an increase in the brittle TiAl₃ phase with increasing ceramic volume at the fracture surface greatly deteriorated the toughness of the Al/TiC composites. Finally, the relationship between cracking mode and structure features in the laminated composites was discussed to account for the toughening mechanism.     

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.     

Interface formation in infiltrated Al(Si)/diamond composites

This study pertains to the investigation of interface formation in infiltrated Al-based composites with high-volume fractions of monocrystalline synthetic diamond particles. The interface characteristics are discussed with respect to process conditions and Al matrix chemistry. To this end, two infiltration techniques, i.e., squeeze-casting and gas pressure infiltration are compared and the effect of Si-addition to the Al matrix is addressed. Eventually, thermal properties of the composite materials are presented and are in turn related to the interface characteristics.Electron microscopy investigations reveal a distinct 50–200-nm-thick layer at the interface between the metal matrix and the diamond particle, regardless of process history and matrix chemistry. This layer is amorphous and consists of carbon, aluminium and oxygen. Additionally, nanocrystallites of Al₂OC and enrichment of Si are observed within this interface layer in the Si-free, squeeze-casted material and in the gas pressure-infiltrated material with 7 wt.% of Si, respectively. Despite the fact that no evidence of SiC is found in the Si-containing composites, the process conditions experienced in gas pressure infiltration are clearly more favourable than those experienced in squeeze casting with respect to interfacial bonding and thermal properties. Actually, between 25 and 50 °C, the gas pressure-infiltrated AlSi/diamond composite yields a thermal conductivity of 375 W/m K along with a coefficient of thermal expansion of 7 × 10^− 6/K.     

Fabrication of Ti3SiC2-based composites via three-dimensional printing: Influence of processing on the final properties

In this work the influence of the processing routes on the microstructure and properties of Ti₃SiC₂-based composites was investigated. The three main processing steps are (i) three-dimensional printing of Ti₃SiC₂ powder blended with dextrin, (ii) pressing of printed samples (uniaxial or cold isostatic pressing), and (iii) sintering of pressed samples at 1600 °C for 2 h. The Ti₃SiC₂-based composites were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Young's Modulus and flexural strength were measured to examine the mechanical properties. Porosity, density, shrinkage, and mass change were measured at each processing step. Those samples uniaxially pressed at 726 MPa presented the highest density, shrinkage, and mass change. However, microstructural morphologies were crack-free and homogeneous for cold isostatic pressed Ti₃SiC₂-based composites as compared to uniaxially pressed samples. The highest values for Young's Modulus (~300 GPa) and flexural strength (~3 GPa) were observed with uniaxially pressed Ti₃SiC₂-based composites.     

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.     

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.