Abnormal mechanical hysteresis behavior of Tyranno-ZMI SiC/SiC containing Ti3Si(Al)C2

This work studied the effect of tough phase Ti₃Si(Al)C₂ on the mechanical hysteresis behavior of SiC/SiC. Different from continuous fibers reinforced brittle ceramic matrix composites, the mechanical hysteresis behavior of SiC/SiC containing Ti₃Si(Al)C₂ shows some abnormal phenomena: as peak applied stress increases during cyclic loading-unloading-reloading tests, the thermal residual stress values exhibit highly dispersion and the thermal misfit relief strain shows abnormally slow growth. These abnormal phenomena are caused by the reduction of transvers cracks (perpendicular to loading fibers) and the generation of hoop cracks (parallel to loading fibers). The plastic deformations of Ti₃Si(Al)C₂ prevents the transverse cracking of modified matrix, while promoting the hoop cracking of SiC matrix prepared by chemical vapor infiltration (CVI-SiC). Hoop cracking occurs within the transition zone containing amorphous SiO₂ layer and carbon layer in CVI-SiC matrix. The combination of weak transition zone and strong modified matrix finally leads to the occurrence of hoop cracking.     

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.     

Improved strength-impairing contact damage resistance of Ti3Si(Al)C2/SiC composites

The resistance of Ti₃Si(Al)C₂-based materials to strength-impairing contact damage was investigated using the Hertzian indentation method. Microstructural analysis indicated that for the three types of testing materials the contact damage was governed by multiple grain slip, crushed grains, and intergranular shear failure. No cone cracking or other macro-cracks were visible on or beneath the contact damage surfaces. Bending tests on the specimens containing single-cycle contact damage revealed that the resistance of Ti₃Si(Al)C₂ to strength degradation was significantly improved by incorporating SiC particles into the matrix. The mechanism of the improvement is ascribed to the increased shear resistance and the fact that the hard SiC particles inhibit the downward extent of the contact damage through restricting the slip and deformation of the Ti₃Si(Al)C₂ grains.     

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.     

Intermediate phases in synthesis of Ti3SiC2 and Ti3Si(Al)C2 solid solutions from elemental powders

In this paper, we investigated the reaction path to synthesize Ti₃SiC₂ by the in situ hot pressing/solid–liquid reaction method. The effect of different content of Al addition on this process was also examined. Ti₃SiC₂ mainly formed from the reaction between Ti₅Si₃C_x, TiC_x, TiSi₂ and graphite at 1400–1500 °C. As an inescapable impurity in Ti₃SiC₂, TiC_x was removed by addition of small amounts of Al. This was owing to the fact that the addition of a minor quantity of Al increased the amount of “effective TiC_x” and relatively decreased that of “invalid TiC_x”. Further increasing Al content, however, resulted in the presence of TiC_x again in the final product. This was due to the fact when significant amounts of Al was added, the stoichiometric ratio of silicon and graphite has been deviated from that for Ti₃SiC₂. More Si and less graphite were needed to prepare a monolithic Ti₃Si(Al)C₂ solid solution with high Al content.     

Multicomponent (Hf0.25Zr0.25Ti0.25Cr0.25)B2 ceramic modified SiC–Si composite coatings: In-situ synthesis and high-temperature oxidation behavior

High-entropy ceramics, a novel type of multicomponent materials with broad application prospects, have stirred up world-wide interests for over a decade. In the current work, in-situ high-entropy (Hf_0.25Zr_0.25Ti_0.25Cr_0.25)B₂ ceramic modified SiC–Si (HETMB₂-SiC-Si) coating was deposited on carbon/carbon (C/C) composites via gaseous reactive infiltration of Si assisted slurry painting (GRSI-SP) method, to improve the oxidation protective ability of C/C composites at 1973 K. The formation and oxidation mechanisms of the coating was explored by first-principles simulation, experiment and thermodynamic analyses. The coating prepared at 2373 K shows dense mosaic structure filled with HETMB₂-rich Si-based multiphase. This coating adheres well with the C/C substrate, which is ascribed to the formed zigzagged SiC–Si transition layer. This coating protected C/Cs from oxidation for more than 205 h at 1973 K. The enhanced oxidation protective ability is mostly ascribed to the subsequently generated compact and stable Hf-Zr-Ti-Cr-Si-O composite oxidation scale. This research will start up novel research ares of developing high-entropy materials modified coatings with improved protective ability under extreme environments.     

Microstructure and mechanical properties of plasma sprayed TiC/Ti5Si3/Ti3SiC2 composite coatings with Al additions

The mass production of MAX phase coatings such as Ti₃SiC₂ and Ti₃AlC₂ using the plasma spraying method is highly challenging due to its ultra-high temperature and short reaction time. In this study, agglomerate powders of 3Ti/SiC/C/xAl with various Al contents (x = 0–1.5) were prepared to form TiC/Ti₅Si₃/Ti₃SiC₂ composite coatings using the plasma spraying technique. The effect of the Al addition on the microstructures and mechanical performances of the as-sprayed coatings was investigated. The addition of Al decreased the TiC content of the coatings while increasing their Ti₃SiC₂ content significantly. The addition of even small amounts of Al improved the MAX phase fraction of the coatings from 8.95 wt% (x = 0) to 34.05 wt% (x = 0.2) and 41.60 wt% (x = 0.5). Excess Al did not affect the Ti₃SiC₂ content of the coatings. The composite coatings showed a lamellar structure with pores and microcracks. With the addition of Al, the microhardness of the coatings increased slightly, while the fracture toughness improved significantly. The composite coatings with Al showed better wear resistance than those without Al. The wear mechanism of the coatings was a combination of adhesive wear, abrasive wear, and oxidative wear.     

Microwave Sintering of Ti3Si(Al)C2 Ceramic

In this work, microwave sintering (MWS) method was successfully applied for fabrication of dense layered ternary Ti₃Si(Al)C₂ ceramic. Compared to conventional pressureless approaches, MWS could significantly decrease preparation temperature from 1600°C to 1400°C. The activation energy of the MWS process was estimated as 233 ± 18 kJ/mol, which was much lower than those in previous sintering techniques. The low sintering temperature likely originates from the low activation energy during MWS process. Such low temperature do not only make the as‐received Ti₃Si(Al)C₂ ceramic much smaller grain size and better mechanical properties, but also indicate higher energy converting efficiency during the sintering processes. Wide application of MWS techniques in MAX phases is expected to promote the practical applications of these materials and contribute to the energy saving during sintering process.     

Effect of Al dopant on the hydrothermal oxidation behavior of Ti3SiC2 powders

Experimental and thermodynamic studies of the hydrothermal oxidation behavior of Ti₃Si_0.9Al_0.1C₂ powders were performed at 500–700 °C under a hydrostatic pressure of 50 MPa. Titanium, silicon and aluminum were selectively extracted from Ti₃Si_0.9Al_0.1C₂ during hydrothermal oxidation, resulting in the formation of oxides and disordered carbon. A comparative investigation with Ti₃SiC₂ disclosed the evident influence of Al dopant on the hydrothermal oxidation process, i.e. delaying the phase transformation from anatase to rutile, promoting the formation of carbon, the crystallization of silica and decomposition of Ti₃Si_0.9Al_0.1C₂. The corresponding mechanism was discussed.     

Wetting of SiC by Al-Ti alloys and joining by in-situ formation of interfacial Ti3Si(Al)C2

Two pressureless and reliable procedures for brazing SiC-based materials have been designed. The joining was obtained by the in-situ formation of a Ti₃Si(Al)C₂ MAX phase using simple Al-Ti interlayers. Wettability studies were conducted using several Al-Ti alloys in contact with SiC at 1500?°C. The interfacial microstructures and thermodynamic analysis demonstrated that liquid Al₃Ti in contact with SiC formed a well-bonded Ti₃Si(Al)C₂ interfacial layer. These findings guided the design of two joining methods: one consisted of the simple infiltration of Al₃Ti into the brazing seam, while an Al₃Ti paste/Ti/Al₃Ti paste interlayer assembly was designed for the second process. Sound interfaces without cracks were obtained in both processes. The average shear strength was very high, 296?MPa, for the infiltration method; the drawback was the presence of residual Al. Joining through Al₃Ti/Ti/Al₃Ti interlayers avoided the presence of low-temperature melting phases, with lower shear strength: 85 or 89?MPa depending on the testing method.     

Al2O3/SiC/(W, Ti)C多相复合陶瓷材料的研究

建立了多相复合陶瓷材料增强相极限体积含量的理论模型,并采用热压工艺制得AI2O3/SiC/(W,Ti)C多相复合陶瓷材料,该材料具有良好的综合力学性能。研究表明：只有在合适的热压工艺和组分条件下才能获得良好的微观结构与力学性能。该陶瓷材料的增韧机制主要是裂纹偏转。此外,大量孪晶和位错的存在对材料的增韧补强也有所贡献。     

Mechanical Behavior and Electromagnetic Interference Shielding Properties of C/SiC–Ti3Si(Al)C2

In this paper, a low‐temperature densification process of Al–Si alloy infiltration was developed to fabricate C/SiC–Ti₃Si(Al)C₂, and then the microstructure, mechanical, and electromagnetic interference (EMI) shielding properties were studied compared with those of C/SiC–Ti₃SiC₂ and C/SiC–Si. The interbundle matrix of C/SiC–Ti₃Si(Al)C₂ is mainly composed of Ti₃Si(Al)C₂, which can bring various microdeformation mechanisms, high damage tolerance, and electrical conductivity, leading to the high effective volume fraction of loading fibers and electrical conductivity of C/SiC–Ti₃Si(Al)C₂. Therefore, C/SiC–Ti₃Si(Al)C₂ shows excellent bending strength of 556 MPa, fracture toughness 21.6 MPa·m^1/2, and EMI shielding effectiveness of 43.9 dB over the frequency of 8.2–12.4 GHz. Compared with C/SiC–Si and C/SiC–Ti₃SiC₂, both the improvement of mechanical properties and EMI shielding effectiveness can be obtained by the introduction of Ti₃Si(Al)C₂ into C/SiC, revealing great potential as structural and functional materials.     

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.     

Oxidation behavior of Ti3SiC2 powder synthesized by using biochar,Si and Ti

Biochar was proposed as a novel carbon source for synthesizing Ti₃SiC₂ powder with high purity by a simple pressureless sintering at 1673 K, and Ti₃SiC₂ grains exhibited the typical nanolayered structure. The oxidation behavior of Ti₃SiC₂ powder showed the parabolic law during isothermal oxidation from 1273 K to 1473 K. Dense and continuous oxidation layer consisting of mixed TiO₂ and SiO₂ was formed rapidly on the surface of Ti₃SiC₂ particles as a diffusion barrier, which effectively retarded the inward diffusion of oxygen, conferring good oxidation resistance of the powder.     

Irradiation Damage in Ti3(Si,Al)C2: a TEM Investigation

Ti₃SiC₂, belonging to MAX phases, is a potential candidate material, which could be incorporated in core components of future gas-cooled fast nuclear reactors (GFR). Despite extensive work on mechanical behavior, corrosion resistance, or electrical properties, data concerning the evolution of Ti₃SiC₂ under irradiation are very limited. In this work, Ti₃(Si,Al)C₂ was irradiated at room temperature with 92 MeV Xe ions to induce irradiation damage. The samples were investigated by transmission electron microscopy (TEM) through front view and cross-section observations, which allowed to follow microstructure changes from 0.02 dpa up to 6.67 dpa. Progressive atomic disorder versus dose was highlighted, leading to extinction of some diffraction spots (at 0.15 dpa) and then diffuse patterns (at 3 dpa). The ABABACAC periodicity related to 3-1-2 MAX phases was lost but the image fringes of basal plans could still be identified and no amorphous ring occurred. This means that Ti₃(Si,Al)C₂ was strongly affected by irradiation but did not turn to amorphous even at 6.67 dpa. This important result was correlated to previous conclusions from X-ray diffraction and nanoindentation analysis and suggests the good behavior of Ti₃(Si,Al)C₂ under irradiation in the target temperature range assigned to GFR.     

Low-temperature diffusion bonding of Ti3Si(Al)C2 ceramic with Au interlayer

Herein, a reliable diffusion bonding of Ti₃Si(Al)C₂ ceramic is achieved by applying Au foil as an interlayer at 650 °C for 30 min with an axial pressure of 20 MPa. This novel method significantly decreases the bonding temperature, which is about 150 °C lower than the lowest bonding temperature from current research to the best of our knowledge. Maximum shear strength of 58 MPa is achieved at 650 °C among the bonding temperature range of 600 °C~800 °C. The microstructure evolution mechanism and the relationship between microstructure and mechanical property are discussed. The facile mutual diffusion of Au with de-intercalated Al and Si from Ti₃Si(Al)C₂ is considered critical in achieving sound interfacial bonding.     

Thermal shock behavior of 3-dimensional C/SiC composite

The thermal shock behavior of a three-dimensional carbon fiber reinforced SiC matrix fabricated by chemical vapor infiltration (CVI) technique was studied using the air quenched method. Damage to composites was assessed by a destructive technique of measuring mechanical properties using three-point flexure and SEM characterization. C/SiC composites displayed good resistance to thermal shock, and retained 83% of the original strength after quenching from 1300 to 300°C 100 times. The critical ΔT of C/SiC in combustion environment was 700°C. The critical number of thermal shocks for the C/SiC composite was about 50 times. When the number of thermal shocks was less than 50 times, the residual flexural strength of C/SiC composites decreased with the increase of thermal shock times. When the number of thermal shocks of C/SiC was greater than 50, the strength of C/SiC did not further decrease because the crack density was saturated.     

Fracture toughness determination of Ti3Si(Al)C2 and Al2O3 using a single gradient notched beam (SGNB) method

In this work, we suggest a new and simple method named single gradient notched beam (SGNB) method for determining the fracture toughness of Ti₃Si(Al)C₂ and Al₂O₃ with four-point bending specimens. For the specimen with a gradient notch, a sharp natural crack will initiate and extends from the tip of the triangle under increasing load. Based on the straight through crack assumption or on the slice model, the stress intensity factor coefficient for this notched beam was derived. The fracture toughness can be calculated from the maximum load and the minimum of the stress intensity factor coefficient without knowing the crack length. To verify the feasibility and reliability of this suggested method, the SGNB method and two other conventional methods, e.g. the chevron notched beam (CNB) method and single edge notched beam (SENB) method, were performed to determine the fracture toughness of Ti₃Si(Al)C₂ and Al₂O₃. The measured fracture toughness values obtained from the SGNB method agreed well with those from conventional fracture toughness tests.     

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.