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.     

Microstructure and mechanical properties of in-situ hot pressed (TiB2 + SiC)/Ti3SiC2 composites with tunable TiB2 content

Without impurity phases detected, fully dense (TiB₂?+?SiC)/Ti₃SiC₂ composites have been successfully synthesised by in-situ reaction hot pressing. The effect of TiB₂ content on phase composite, sintering properties, microstructure, and mechanical properties of the composites were thoroughly investigated. With TiB₂ content increasing from 0 to 50?vol.-%, the flexural strength increases first and then decreases, whereas fracture toughness, hardness and modulus show a linear increase. The maximum strength of 826?MPa was obtained at 20?vol.-% TiB₂. On the whole, the (TiB₂?+?SiC)/Ti₃SiC₂ composites exhibit a superior comprehensive mechanical properties superior to other reported Ti₃SiC₂-based composites reinforced by singular reinforcement. The significant strengthening and toughening effect induced by the in-situ incorporated TiB₂ can be ascribed to the unique properties of TiB₂ and the synergistic action of many mechanisms including particle reinforcement, pulling out of grains, crack deflection and grain refinement strengthening.     

Synthesis,microstructure, and mechanical properties of TiC-SiC-Ti3SiC2 composites prepared by in situ reactive hot pressing

In this work, TiC-SiC-Ti₃SiC₂ composites were synthesized by in situ reactive hot pressing using β-SiC, graphite, and TiH₂ powders as initial materials. Microstructure and mechanical properties of as-prepared dense composites were systematically investigated. It was found that by increasing the initial SiC content the final SiC content in the composites increased in contrast to the decrease in TiC and Ti₃SiC₂ contents. In the dense composites, TiC and Ti₃SiC₂ grains exhibited transgranular fracture, whereas SiC particles showed intergranular fracture. The composite containing 77 vol.% TiC, 4 vol.% SiC, and 19 vol.% Ti₃SiC₂ had the highest flexural strength of 706.6 MPa. The composite consisting of 44 vol.% TiC, 49 vol.% SiC, and 7 vol.% Ti₃SiC₂ exhibited the highest Vickers hardness of 22.3 GPa and the highest fracture toughness of 6.0 MPa·m^1/2.     

Effect of thermal stability of Mn+1AXn phases on microstructure and mechanical properties of Mn+1AXn/ZA27 composites

Special layered structure endows ternary M_n+1AX_n phase ceramics with good electrical and thermal conductivity, excellent abrasive resistance, and perfect thermal shock resistance. In this work, three kinds of M_n+1AX_n phase ceramics (Ti₃SiC₂, Ti₃AlC₂, and Ti₂SnC) were chosen to reinforce the ZA27 alloys, respectively. By employing “two-step sintering” technology which is pressureless sintered at 870°C for 1 h firstly and then hot pressed at 500°C for 1 h, M_n+1AX_n/ZA27 composites were successfully fabricated. The effects of thermal stability of the above M_n+1AX_n on microstructure, mechanical properties, and friction performance of the three M_n+1AX_n/ZA27 composites were investigated. The different reaction degrees between the three M_n+1AX_n reinforcements and the ZA27 matrix were ascribed to the differences of chemical bond energy. The results demonstrated that at the sintering temperature of 870°C, Ti₂SnC was completely reacted in Ti₂SnC/ZA27 composite, and Ti₃AlC₂ partially reacted in ZA27 matrix, while no reaction happened between Ti₃SiC₂ and ZA27 matrix. Hence, the order of thermal stability for the three M_n+1AX_n phases in ZA27 matrix is Ti₃SiC₂ > Ti₃AlC₂ > Ti₂SnC. Besides, Ti₃AlC₂/ZA27 composites possess the best mechanical properties and wear resistance, which was attributed to interfacial reaction improved the boding between matrix and reinforcement.     

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.     

Formation of Ti3SiC2 interphase coating on SiCf/SiC composite by electrophoretic deposition

To improve the oxidation resistance of SiC composites at high temperature, the feasibility of using Ti₃SiC₂ coated via electrophoretic deposition (EPD) as a SiC fiber reinforced SiC composite interphase material was studied. Through fiber pullout, Ti₃SiC₂, due to its lamellar structure, has the possibility of improving the fracture toughness of SiC_f/SiC composites. In this study, Ti₃SiC₂ coating was produced by EPD on SiC fiber; using Ti₃SiC₂‐coated SiC fabric, SiC_f/SiC composite was fabricated by hot pressing. Platelet Ti₃SiC₂ powder pulverized into nanoparticles through high‐energy wet ball milling was uniformly coated on the SiC fiber in a direction in which the basal plane of the particles was parallel to the fiber. In a 3‐point bending test of the SiC_f/SiC composite using Ti₃SiC₂‐coated SiC fabric, the SiC_f/SiC composite exhibited brittle fracture behavior, but an abrupt slope change in the strength‐displacement curve was observed during loading due to the Ti₃SiC₂ interphase. On the fracture surface, delamination between each layer of SiC fabric was observed.     

Fabrication of Ti3SiC2-Ti4SiC3-SiC ceramic composites through carbosilicothermic reduction of TiO2

Dense Ti₃SiC₂-SiC, Ti₄SiC₃-SiC, and Ti₃SiC₂-Ti₄SiC₃-SiC ceramic composites were fabricated through carbosilicothermic reduction of TiO₂ under vacuum, followed by hot pressing of the as-synthesized products under 25 MPa at 1600°C. In the reduction step, SiC either alone or in combination with elemental Si was used as a reductant. A one-third excess of SiC was added in the reaction mixtures in order to ensure the presence of approximately 30 vol.% SiC in the products of synthesis. During the hot pressing step, the samples that contained Ti₃SiC₂ showed better densification compared to those containing Ti₄SiC₃. The obtained composites exhibited the strength properties typical of coarse-grained MAX-phase ceramics. The flexural strength values of 424 and 321 MPa were achieved in Ti₃SiC₂-SiC, and Ti₃SiC₂-Ti₄SiC₃-SiC composites, respectively. The fracture toughness values were 5.7 MPa·m^1/2.     

Microstructure and mechanical properties of Ti3SiC2/3Y-TZP composites by spark plasma sintering

Ti₃SiC₂/3Y-TZP (3 mol% Yttria-stabilized tetragonal zirconia polycrystal) composites were fabricated by spark plasma sintering (SPS). The effect of Ti₃SiC₂ content on room-temperature mechanical properties and microstructures of the composites were investigated. The Vickers hardness and bending strength of the composites decreased with the increasing of Ti₃SiC₂ content whereas the fracture toughness increased. The maximum fracture toughness of 9.88 MPa m^1/2 was achieved for the composite with 50 vol.% Ti₃SiC₂. The improvement of the fracture toughness is owing to the crack deflection, crack bridging, the transformation toughening effects.     

Microstructure and mechanical properties of in situ produced Ti5Si3/TiC nanocomposites

The microstructure and mechanical properties of in situ produced Ti₅Si₃/TiC nanocomposites have been studied. Ti₅Si₃/TiC composites have been prepared by reaction hot pressing mixed powders of elemental Ti, Si and SiC. XRD, SEM, TEM were employed to characterize the structure of the composites. When no elemental Si is added, the resulting composite contains 65 vol.% Ti₅Si₃, with a small amount of carbon dissolved in it. The majority of the TiC particles are nanosized. A small fraction Ti₃SiC₂ grains, with an average size 100 nm, are located in the TiC particles while other elongated Ti₃SiC₂ grains in the Ti₅Si₃ matrix. The highest bending strength of the Ti₅Si₃/TiC composites is 510 MPa at room temperature, which is approximately 6 times that of the monolithic Ti₅Si₃ material. The fracture toughness of the composites exceeds that of pure Ti₅Si₃, and at 1100°C, the yield strength of Ti₅Si₃/35TiC reaches 800 MPa.     

In-situ formation of Ti3SiC2 interphase in SiCf/SiC composites by molten salt synthesis

Titanium silicon carbide (Ti₃SiC₂) film was synthesized by molten salt synthesis route of titanium and silicon powder based on polymer-derived SiC fibre substrate. The pre-deposited pyrolytic carbon (PyC) coating on the fibre was utilized as the template and a reactant for Ti₃SiC₂ film. The morphology, microstructure and composition of the film product were characterized. Two Ti₃SiC₂ layers form the whole film, where the Ti₃SiC₂ grains have different features. The synthesis mechanism has been discussed from the thickness of PyC and the batching ratio of mixed powder respectively. Finally, the obtained Ti₃SiC₂ film was utilized as interphase to prepare the SiC fibre reinforced SiC matrix composites (SiC_f/Ti₃SiC₂/SiC composites). The flexural strength (σ_F) and fracture toughness (K_IC) of the SiC_f/Ti₃SiC₂/SiC composite is 460 ± 20 MPa and 16.8 ± 2.4 MPa?m^1/2 respectively.     

Microstructure and Mechanical Properties of (TiB2 + SiC) Reinforced Ti3SiC2 Composites Synthesized by In Situ Hot Pressing

Fully dense (TiB₂ + SiC) reinforced Ti₃SiC₂ composites with 15 vol% TiB₂ and 0–15 vol% SiC were designed and synthesized by in situ reaction hot pressing. The increase in SiC content promoted densification and significantly inhibited the growth of Ti₃SiC₂ grains. The in situ incorporated TiB₂ and SiC reinforcements showed columnar and equiaxed grains, respectively, providing a strengthening–toughening effect by the synergistic action of particulate reinforcement, grain's pulling out, “self‐reinforcement,” crack deflection, and grain refining. A maximum bending strength of 881 MPa and a fracture toughness of 9.24 MPam^1/2 were obtained at 10 vol% SiC. The Vickers hardness of the composites increased monotonously from 9.6 to 12.5 GPa.     

Perpetual effect of laser surface texturing on tribological properties of Ti3SiC2/GNP composite—A fretting wear study

Tribological properties of Ti₃SiC₂ ceramic and Ti₃SiC₂/GNP composite were investigated using fretting sliding against Si₃N₄ ball counter body at a load of 50 N for a sliding distance of 900 m, under non-textured lubricated (NTL), textured lubricated (TL) condition, and textured lubricated high temperature (TLHT). This paper presents the influence of laser surface texturing (LST) on Ti₃SiC₂ and its graphene nanoplatelets (GNP) reinforced composite established through spark plasma sintering (SPS), tested under fretting wear conditions. The coefficient of friction and wear rate of Ti₃SiC₂ and its graphene nanoplatelets reinforced composites were incontrovertibly enhanced with laser surface texturing as compared to non-textured Ti₃SiC₂ and its GNP composite. The TL surface of Ti₃SiC₂ composite reinforced with 15% GNP showed the lowest COF and wear rate. Almost negligible changes were observed for TLHT tests. The LST proved to an efficient technique for enhancing the friction and wear properties of Ti₃SiC₂ and Ti₃SiC₂/GNP composite.     

Effects of SiC nanowires and whiskers on high-entropy carbide-based composites sintered at low and high temperatures

This study aimed to investigate the toughening effects of SiC nanowires (SiC_nw) and SiC whiskers (SiC_w) on high-entropy carbide based composites prepared at different temperatures (1600°C and 2000°C). At low temperature (1600°C), SiC_nw and SiC_w maintain their original morphology and properties, and exhibit the good toughening effects. The SiC_nw with larger aspect ratio and more curly wires exhibit a much stronger toughening effect on the (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8 composites reinforced with 15 vol.% SiC_nw, which shows the highest value of fracture toughness about 6.7 MPa∙m^1/2. However, at high sintering temperature (2000°C), SiC_nw and SiC_w are prone to thermal-induced damages, which significantly reduces their mechanical properties, and thus, toughening effects on (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8 composites. The addition of SiC_w, which have better thermal stability at 2000°C, results in the (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8–15 vol.% SiC_w composite exhibiting relatively better fracture toughness, about 3.7 MPa∙m^1/2. Based on the results of the current study, the critical influence of SiC_nw and SiC_w on the toughening of (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8 composites is highly dependent on their high-temperature thermal stability.     

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.     

Mechanical properties of SiCp/Al2O3 ceramic matrix composites prepared by directed oxidation of an aluminum alloy

Silicon carbide particulate reinforced alumina matrix composites were fabricated using DIrected Metal OXidation (DIMOX) process. Continuous oxidation of an Al-Si-Mg-Zn alloy with appropriate dopants along with a preform of silicon carbide has led to the formation of alumina matrix surrounding silicon carbide particulates. SiC_p/Al₂O₃ ceramic matrix composites fabricated by the DIMOX process, possess enhanced mechanical properties such as flexural strength, fracture toughness and wear resistance, all at an affordable cost of fabrication. SiC_p/Al₂O₃ matrix composites were investigated for mechanical properties such as flexural strength, fracture toughness and hardness; the composite specimens were evaluated using standard procedures recommended by the ASTM. The SiC_p/Al₂O₃ ceramic matrix composites with SiC volume fractions from 0.35 to 0.43 were found to possess average bend strength in range 158-230 MPa and fracture toughness was found to be in range of 5.61-4.01 MPa√m. The specimen fractured under three-point loading as observed under scanning electron microscope was found to fail in brittle manner being the dominant mode. Further the composites were found to possess lower levels of porosity, among those prepared by DIMOX process.     

Joining of Ti-coated monolithic SiC using a SiCw/Ti3SiC2 filler by electric field-assisted sintering

Monolithic SiC, for the first time, was successfully joined using a SiC whisker-reinforced Ti₃SiC₂ composite (SiC_w/Ti₃SiC₂) filler via electric field-assisted sintering technique. A thin Ti coating layer was formed on the SiC surface to minimize the residual stress at the joint interface by transforming it into a TiC gradient layer. After optimizing process parameters, a joint strength higher than 250 MPa was obtained, which is higher than the other values reported in the literature. Failure occurred at the SiC base rather than the joining interface because of the improved joint strength by the incorporation of SiC_w. The addition up to 15 wt. % SiC_w in the filler layer improved the joint strength by various strengthening mechanisms. On the other hand, the joint strength was lower with 20 wt. % SiC_w addition, indicating the importance of thermal expansion mismatch between SiC_w and Ti₃SiC₂ to obtain a sound SiC joint.     

Fast seamless joining of SiCw/Ti3SiC2 composite using electric field-assisted sintering technique

A pair of Ti₃SiC₂ reinforced with SiC whiskers (SiC_w/Ti₃SiC₂) composites was successfully joined without any joining materials using electric field-assisted sintering technology at a temperature as low as 1090°C (T_i) and a short time of 30 s. The microstructure and mechanical properties of the obtained SiC_w/Ti₃SiC₂ joints were investigated. The solid-state diffusion was the main joining mechanism, which was facilitated by a relatively high current density (~586 A/cm²) at the joining interface. The shear strength of the sample joined at 1090°C was 51.8 ± 2.9 MPa. The sample joined at 1090°C failed in the matrix rather than at the interface, which confirmed that a sound inter-diffusion bonding was obtained. A rapid and high efficient self-joining process may find application in the case of SiC_w/Ti₃SiC₂ sealing cladding tube and end cap.     

Influence of Ti3SiC2 content on erosion behavior of Cu–Ti3SiC2 cathode under vacuum arc

In this study, a series of Cu–Ti₃SiC₂ composites with different Ti₃SiC₂ contents were prepared by spark plasma sintering. Their mechanical properties and electrical resistivity were investigated. Through analyzing the morphology and composition of the eroded regions, the effect of Ti₃SiC₂ content on the erosion behavior of Cu–Ti₃SiC₂ cathodes under vacuum arc was studied. Results show that the relative density and bending strength of the Cu–Ti₃SiC₂ composites decrease with the increasing Ti₃SiC₂ content, while the opposite holds for hardness and electrical resistivity. The morphology and phase composition of the erosion zone is dominated by the decomposition process and the amount of Ti₃SiC₂ in the cathode. Cu–Ti₃SiC₂ cathodes containing 10 mass%Ti₃SiC₂ or less displayed relatively flat eroded surface morphology. Cathodes with high Ti₃SiC₂ content suffered more serious erosion with voids, cracks, and severe decomposition of Ti₃SiC₂, all of which contribute to impairing the arc ablation resistance of the composite. Ti₃SiC₂ particles decomposed into TiC and Si vapor; eventually, this TiC also decomposed into Ti vapor and C, leaving a considerable amount of C on the arc affected cathode surface. Excess addition of Ti₃SiC₂ particles not only deteriorates the strength but also the electrical and thermal conductivity of the composite, both of which in turn harms the arc erosion resistance of the material. These results suggest that the optimal Ti₃SiC₂ content is below 10 mass% in the composite.     

Interfacial microstructure and mechanical properties of TC4/Ti3SiC2 contact-reactive brazed joints using a Cu interlayer

Reliable contact-reactive brazed joints of TC4 alloy and Ti₃SiC₂ ceramic were obtained using a Cu interlayer. The interfacial microstructure of a TC4/Ti₃SiC₂ joint brazed at 920?°C for 10?min was TC4/Ti₂Cu +?α-Ti +?β-Ti/Ti₂Cu +?AlCu₂Ti +?Ti₅Si₃/Ti₅Si₃ +?Ti₅Si₄/Ti₃SiC₂. The interfacial microstructure and mechanical properties of TC4/Ti₃SiC₂ joints brazed at different temperatures were investigated. With increasing temperature, the shear strength of the brazed joints first increased and then decreased. The maximum shear strength was 132?±?8?MPa, and the corresponding fracture occurred along the Ti–Si reaction layer and the Ti₃SiC₂ substrate adjacent to the Ti–Si reaction layer. The microhardness test also demonstrated that the Ti–Si reaction layer possessed the highest microhardness, 812?±?22 HV. The Ti-Si reaction layer was the weakest part of the brazed joints. To eliminate the Ti-Si reaction layer and improve the mechanical properties of TC4/Ti₃SiC₂ brazed joints, a 40-μm Ni layer was plated on the surface of the Ti₃SiC₂ ceramic before brazing. The results showed that the Ti–Si reaction layer that formed adjacent to the Ti₃SiC₂ ceramic was thin and intermittent. Moreover, the interface between the Ti₃SiC₂ ceramic and the TC4 alloy became jagged. The shear strength of the TC4/nickel-plated Ti₃SiC₂ brazed joints improved to 148?±?8?MPa; the corresponding fracture occurred mainly in the Ti₃SiC₂ ceramic and only a small portion of the fracture occurred in the brazing seam.     

Oxidation resistance,ablation resistance and in situ ceramization mechanism of Al-coated carbon fiber/boron phenolic resin ceramizable composites modified with Ti3SiC2

Inherent defect of easy oxidation limited further application of carbon fiber/phenolic resin composites in hostile environments. Herein, a combined strategy of matrix modification and fiber coating was proposed to fabricate a novel ceramizable composite containing Al-coated carbon fibers and Ti₃SiC₂ toward thermal protection materials (TPM), which offered a promising solution to challenge facing long-term thermal protection and load-bearing subject to severe oxidation corrosion and ablation in hypersonic vehicle applications. Oxidation resistance, mechanical strength evolution, phase evolution, microstructure evolution and mechanical strength failure mechanism at elevated temperatures were studied based on thermogravimetric analysis, static ablation test, mechanical test, X-ray diffraction analysis, and scanning electron microscopy coupled with energy dispersive X-ray analysis. The resulting composites exhibited outstanding oxidation resistance, with residue yield at 1600 °C and flexural strength at 1400 °C as high as 87.7% and 31.7 MPa, respectively. It was found that dense multiphase ceramics formed by reactions between Ti₃SiC₂, O₂, pyrolytic carbon (PyC) and N₂, acted as oxygen barriers and self-healing agents during static ablation. Besides, the resulting composites exhibited satisfactory ablation resistance and the linear ablation rate was as low as 0.00853 mm/s. Furthermore, ablation mechanisms were revealed based on phase identification, microstructure characterization and thermodynamic calculation analysis. It was revealed that multiphase ceramics composed of PyC, Al coatings, Ti₃SiC₂, TiC, Al₂OC and AlB₂ contributed great to the ablation resistance during oxyacetylene ablation.