Effect of temperature on the structure and mechanical properties of SiC–TiB2 composite ceramics by solid-phase spark plasma sintering

SiC composite ceramics have good mechanical properties. In this study, the effect of temperature on the microstructure and mechanical properties of SiC–TiB₂ composite ceramics by solid-phase spark plasma sintering (SPS) was investigated. SiC–TiB₂ composite ceramics were prepared by SPS method with graphite powder as sintering additive and kept at 1700 °C, 1750 °C, 1800 °C and 50 MPa for 10min.The experimental results show that the proper TiB₂ addition can obviously increase the mechanical properties of SiC–TiB₂ composite ceramics. Higher sintering temperature results in the aggregation and growth of second-phase TiB₂ grains, which decreases the mechanical properties of SiC–TiB₂ composite ceramics. Good mechanical properties were obtained at 1750 °C, with a density of 97.3%, Vickers hardness of 26.68 GPa, bending strength of 380 MPa and fracture toughness of 5.16 MPa m^1/2.     

Microstructure and mechanical properties of TiB2–B4C ceramics fabricated by hot-pressing

In this study, TiB₂–B₄C composite ceramics were prepared using Y₂O₃ and Al₂O₃ as the sintering aids. Different contents of B₄C were added to seek promoted comprehensive mechanical properties of the composites. The mixed powders were sintered at 1850 °C under a uniaxial loading of 30 MPa for 2 h via hot-pressing. Through the measurement of XRD, SEM and related mechanical properties, the influence of B₄C content on the microstructure and mechanical properties of TiB₂–B₄C composites ceramics was discussed. The experimental results show that TiB₂–B₄C composite ceramics exhibit excellent mechanical properties, which can be attributed to the dense microstructure and fine grain size. In addition, TiB₂–B₄C composite ceramic shows a relatively high comprehensive properties when the addition amount of B₄C is 20 wt%. The relative density, Vickers hardness, fracture toughness and flexural strength are measured to be 99.61%, 27.63 ± 1.73 GPa, 4.77 ± 0.06 MPa m^1/2, 612.5 ± 28.78 MPa, respectively.     

Microstructure and properties of bilayered B4C-based ceramics

Bilayered B₄C-based ceramics were obtained by hot-pressing. Microstructure, mechanical and ballistic properties of the bilayered ceramics were investigated. One layer was obtained upon addition of Ti and C to the hard B₄C matrix, the newly formed TiB₂ phase uniformly distributed in the matrix. The other layer included variable amounts of Ti₃SiC₂, equal to 10, 20, 30, 40 wt%, and the B₄C-SiC matrix in a fixed weight ratio of 7:3. The amount of TiB₂ and SiC phases, deriving from Ti₃SiC₂ decomposition upon sintering, increased with increasing the Ti₃SiC₂ content. The flexural strength and fracture toughness of bilayered ceramics both increased with increasing the Ti₃SiC₂ content from 10 to 40 wt%. Ballistic testing showed that the B₄C-based ceramic target containing 30 wt% Ti₃SiC₂ broken into pieces upon being impacted by a 12.7 mm armor-piercing incendiary (API) projectile, and effectively consumed the bullet energy and protected the backing plate from serious damage.     

Preparation and microstructure of 3D framework TiC–TiB2 ceramics and their reinforced steel matrix composites

An efficient method for in-situ fabrication of a three-dimensional framework based on heterogeneous TiC–TiB₂ materials with different B₄C content has been reported in the present study. Interpenetrating TiC–TiB₂/steel composites were subsequently prepared by infiltrating molten steel into TiC–TiB₂ framework. The XRD and SEM analyses confirmed that three-dimensional ceramics framework mainly consisted of heterogeneous TiC–TiB₂ phases with the ceramic particles closely connected with each other. TiC–TiB₂ ceramics framework exhibited a high porosity in the range 87.11%–95.95% and low bulk density of 0.17–0.22 g/cm³. The sample with ceramic framework containing 20 wt% B₄C exhibited the strongly continuous microstructure, whereas the sample with ceramic framework containing 25 wt% B₄C had the weakly continuous framework. The Vickers hardness and fracture toughness in the composites reached 284.5 HV and 23.7 MPa m^1/2, respectively. An optimal TiC: TiB₂ mass ratio of 37:55 could effectively inhibit the decomposition of TiB₂ in the molten steel. Inspecting the fracture surface, the dominated fracture modes was noted to be the quasi-cleavage and trans-granular dimple fracture, which could be attributed to novel three-dimensional bi-continuous structure formed between ceramic framework and steel substrate.     

Strengthening and toughening of TiN-based and TiB2-based ceramic tool materials with HfC additive

Effects of HfC addition on the microstructures and mechanical properties of TiN-based and TiB₂-based ceramic tool materials have been investigated. Their pore number decreased gradually and relative densities increased progressively when the HfC content increased from 15 wt% to 25 wt%. The achieved high relative densities to some extent derived from the high sintering pressure and the metal phases. HfC grains of about 1 µm evenly dispersed in these materials. Both TiN and TiB₂ grains become smaller with increasing HfC content from 15 wt% to 25 wt%, which indicated that HfC additive can inhibit TiN grain and TiB₂ grain growth, leading to the formation of a fine microstructure advantageous to improve flexural strength. Especially, TiB₂-HfC ceramics exhibited the typical core-rim structure that can enhance flexural strength and fracture toughness. The toughening mechanisms of TiB₂-HfC ceramics mainly included the pullout of HfC grain, crack deflection, crack bridging, transgranular fracture and the core-rim structure, while the toughening mechanisms of TiN-HfC ceramics mainly included pullout of HfC grain, fine grain, crack deflection and crack bridging. Besides, HfC hardness had an important influence on the hardness of these materials. Higher HfC content increased Vickers hardness of TiN-HfC composite, but lowered Vickers hardness of TiB₂-HfC composite, being HfC hardness higher than for TiN while HfC hardness is lower than for TiB₂. The decrease of fracture toughness of TiN-HfC ceramic tool materials with the increase of HfC content was attributed to the formation of a weaker interface strength.     

In situ TiBX/TiXNiY/TiC reinforced Ni60 composites by laser cladding and its effect on the tribological properties

Ni-based composite coatings reinforced by TiB_X/Ti_XNi_Y/TiC with different Ti6Al4V contents were precipitated on a 35CrMoV substrate via laser cladding. The phase composition, elemental distribution, and precipitated phases of the coatings were characterised using X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy. The mechanical and tribological properties of the cladding layer were also characterised. The results showed that the coating contained TiB₂, TiC, TiB, Ni₃Ti, and NiTi₂ phases with uniform elemental distribution and grain refinement. A schematic of the growth model and precipitation sequence of the reinforced phases was generated. The microstructure, elemental segregation, hardness, and friction behaviour of the cladding layer were significantly influenced by the addition of Ti6Al4V. The optimal microstructure and best mechanical properties were obtained by the addition of 4 wt% Ti6Al4V, with that coating possessing a hardness, average friction coefficient, and wear volume of 770.8 HV₁, 0.180 and 6132 um³, respectively.     

Rapid synthesis of Ti3AlC2/TiB2 composites by the spark plasma sintering (SPS) technique

Dense Ti₃AlC₂/TiB₂ composites were successfully fabricated from B₄C/TiC/Ti/Al powders by spark plasma sintering (SPS). The microstructure, flexural strength and fracture toughness of the composites were investigated. The experimental results indicate that the Vickers hardness increased with the increase in TiB₂ content. The maximum flexural strength (700 ± 10 MPa) and fracture toughness (7.0 ± 0.2 MPa m^1/2) were achieved through addition of 10 vol.% TiB₂, however, a slight decrease in the other mechanical properties was observed with TiB₂ addition higher than 10 vol.%, which is believed to be due to TiB₂ agglomeration.     

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.     

Effects of TiN content on the properties of hot pressed TiB2–SiC ceramics

This research intended to study the impacts of different contents of the TiN additive on the mechanical properties and microstructural features of the TiB₂–SiC-based composites. Three different samples of TiB₂-15 vol% SiC- x vol% TiN (x = 0, 3.5, and 7) were produced by hot-pressing at 2000 °C under 35 MPa for 120 min. Thanks to advancement of some reactions among the TiB₂ surface oxides and the SiC reinforcement, two in-situ phases of TiC and SiO₂ were produced during the sintering. Nevertheless, the TiN incorporation resulted in generating another in-situ compound (TiC_0.3N_0.7) in the relevant as-sintered ceramics. Moreover, introducing TiN significantly refined the microstructure of the composites, leading to higher mechanical characteristics. Finally, the highest flexural strength (781 MPa) and Vickers hardness (27.1 GPa) values were attained for the sample introduced by 7 vol% TiN.     

Design and optimization of TiB2-based ceramic tool materials based on fuzzy theory

Based on the material properties and fuzzy theory, a new design method of TiB₂-based composite ceramic tool material was proposed, and the TiB₂-based composite ceramic tool material with excellent friction and wear resistance was designed. Initially, the fuzzy evaluation method was used to establish the matrix of the friction and wear resistance of the material, and the TiB₂-based material component with excellent friction and wear resistance was determined. Ultimately, based on the principle of fuzzy cognitive map, the correlation mapping of “sintering process–microstructure–mechanical properties” was established, and the composition ratio and sintering process were optimized. The results show that the TiB₂–TaC–TiC ceramic tool material had excellent friction and wear resistance. When the volume content of TaC was 8 vol.%, the volume content of TiC was 20 vol.%, the heating rate was 100°C/min, the holding time was 8 min, the sintering temperature was 1600°C, and the sintering pressure was 50 MPa, the mechanical properties were hardness 23.5 GPa, bending strength 438 MPa, and fracture toughness 10.26 MPa∙m^1/2.     

Novel (Zr,Ti)B2-(Zr,Ti)C-SiC ceramics via reactive hot pressing

Fully dense (Zr, Ti)B₂-(Zr, Ti)C-SiC ceramics were prepared by reactive hot-pressing using ZrB₂, TiC, and SiC as the initial materials for the first time. Effects of SiC addition on the microstructure evolution and mechanical properties were reported. The in-situ reaction between ZrB₂ and TiC as well as the SiC addition leads to the grain refinement. Besides, elongated (Zr, Ti)B₂ plate-like grains are obtained due to the occurrence of a transient liquid phase, which leads to the crack deflection in the matrix effectively. Mechanical properties are improved significantly due to grain-refinement and solid solution strengthening, and plate-like grains toughening effects. The ZrB₂-10 mol%TiC composite with 10 mol% SiC additional exhibits good comprehensive mechanical properties of the hardness of 20.2 GPa, the flexural strength of 803 MPa, and the fracture toughness of 5.7 MPa m^1/2.     

Characterization of triplet Ti–TiB–TiC composites: Comparison of in-situ formation and ex-situ addition of TiC

Four hybrid titanium-based samples with different amounts of B₄C as reinforcement and the same numbers of specimens with TiB₂ + TiC additives were produced using the SPS method at 1200 °C. For a reliable comparison, stoichiometry relations of starting powders were applied to estimate the precise contents of mentioned reinforcements to reach the same vol% of final TiB and TiC phases. The microstructure, relative density (RD), and mechanical properties of both series of SPSed composite samples were studied to make a reliable comparison. The best value of the RD (99.9%) was achieved for the sample doped with 0.48 wt% B₄C. The in-situ TiB_w phase formation in both series of samples was confirmed using XRD and microscopical evaluations. Samples doped with B₄C exhibited better UTS, tensile elongation, and bending strength than the ones doped with TiB₂ + TiC. The sample with the least B₄C content presented the best value of mentioned mechanical properties.     

Preparation,mechanical properties,and toughening mechanisms of SiCw/SiCp-reinforced zirconia-toughened alumina ceramics

Zirconia-toughened alumina (ZTA) ceramics with high mechanical properties were sintered by hot-pressing method using SiC particles (SiCp) and SiC whiskers (SiCw) as the reinforcing agents simultaneously. The influences of sintering temperature, SiCp, and SiCw contents on the microstructure and mechanical properties of ZTA ceramics were investigated. It was found that both SiCp and SiCw could contribute to grain refinement significantly and promote the mechanical properties of the ceramics. However, the excess addition of SiCp or SiCw led to the formation of pores with large sizes and degraded the mechanical properties instead. When 13 wt% SiCp was introduced, the maximum flexural strength of 1180.0 MPa and fracture toughness of 15.9 MPa·m^1/2 were obtained, whereas the maximum flexural strength of 1314.0 MPa and fracture toughness of 14.7 MPa·m^1/2 were achieved at 20 wt% SiCw. Interestingly, the simultaneous addition of SiCp and SiCw could further improve the mechanical properties, and the highest flexural strength of 1334.0 MPa and fracture toughness of 16.0 MPa·m^1/2 were achieved at a SiCw/SiCp ratio of 16/4. The reinforcement mechanisms in the ceramics mainly included the phase transformation toughening of ZrO₂, the crack deflection and bridging of SiCp and SiCw, and the pull-out of SiCw.     

High-performance B4C–TiB2–SiC composites with tuneable properties fabricated by reactive hot pressing

In this work, we systematically studied the effects of powder characteristics (B₄C, TiC and Si powders) on the existential form of toughening phases (SiC and TiB₂) as well as the overall microstructure and properties of B₄C–TiB₂–SiC composites fabricated by reactive hot pressing. The particle size of the TiC powder plays a largely determining role in the development of novel toughening phases, the TiB₂–SiC composite structure, that are formed in the B₄C matrix, while the Si particle size affects the agglomerate level of the SiC phase. The TiB₂–SiC composite structure and SiC agglomerates enhance the fracture toughness, but decrease the flexural strength. Both the microstructure and mechanical properties of B₄C–TiB₂–SiC composites can be effectively tuned by regulating the combinations of the particle sizes of the starting powders. The B₄C–TiB₂–SiC composites demonstrate flexural strength, fracture toughness and Vickers hardness in the respective range of 567–632 MPa, 5.11–6.38 MPa m^1/2, and 34.8–35.6 GPa.     

High-strength TiB2-B4C composite ceramics sintered by spark plasma sintering

Spark plasma sintering (SPS) is an advanced sintering technique because of its fast sintering speed and short dwelling time. In this study, TiB₂, Y₂O₃, Al₂O₃, and different contents of B₄C were used as the raw materials to synthesize TiB₂-B₄C composites ceramics at 1850°C under a uniaxial loading of 48 MPa for 10 min via SPS in vacuum. The influence of different B₄C content on the microstructure and mechanical properties of TiB₂-B₄C composites ceramics are explored. The experimental results show that TiB₂-B₄C composite ceramic achieves relatively good comprehensive properties and exceptionally excellent flexural strength when the addition amount of B₄C reaches 10 wt.%. Its relative density, Vickers hardness, fracture toughness, and flexural strength reach to 99.20%, 24.65 ± .66 GPa, 3.16 MPa·m^1/2, 730.65 ± 74.11 MPa, respectively.     

Integrated high strength and high toughness induced by elongated TiB2 grains in reactive sintered TiB2–TiC–SiC ceramics

Although the addition of other phases into TiB₂ matrix to form ceramic composites has been widely used to improve the mechanical properties of monolithic TiB₂ ceramics, it is still difficult to greatly enhance the flexural strength and fracture toughness simultaneously. In this work, TiB₂–TiC–SiC composites were successfully prepared by reactive spark plasma sintering of Ti₃SiC₂–B₄C–Ti powder mixtures. During the sintering process, TiB₂ grains grew into an elongated morphology, endowing the composites with integrated high strength and high toughness. The growth mechanism of TiB₂ grains was attributed to the evaporation–condensation kinetics induced by the presence of B₂O₃. These findings can accelerate the exploration of ceramic composites with excellent comprehensive properties.     

Influence of Y2O3 on the microstructure and tribological properties of Ti-based wear-resistant laser-clad layers on TC4 alloy

Multi-track Ti-based wear-resistant composite coatings were fabricated on TC4 alloy surfaces using laser-clad TC4 + Ni45 + Co–WC mixed powders with different Y₂O₃ contents (0, 1, and 3 wt%). The microstructure, microhardness, and tribological properties of the coatings were characterised using X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, electron probe X-ray micro analyser, microhardness tester, and friction and wear testing apparatus. The results showed that the number of cracks on the coating surfaces gradually decreased with the addition of Y₂O₃ and that residual Co–WC powders existed in the coating subsurfaces. The phase composition of the coatings with different Y₂O₃ contents remained unchanged and was mainly composed of reinforcing phases of TiC, TiB₂, Ti₂Ni, and matrix α-Ti. With the addition of Y₂O₃, the coating microstructure was remarkably refined, the direction characteristic of the TiC dendrites obviously weakened, and the nucleation rate significantly increased. When the added Y₂O₃ was 3 wt%, a large amount of TiB₂–TiC-dependent growth composite phases precipitated in the coating. The two-dimensional lattice misfit between (0001)_TiB2 and (111)_TiC was 0.912%, which indicated that TiB₂ and TiC formed a coherent interface. When the amount of Y₂O₃ was increased, the microhardness of the coatings gradually decreased, and the wear volume of the coatings first increased and then decreased. Under the effect of the TiB₂–TiC composite phases, the wear resistance of the 3 wt% Y₂O₃ coating was optimal. The 3 wt% Y₂O₃ coating friction coefficient was the lowest, and the wear mechanism was abrasive wear.     

Bulk ultrahard composites in the eutectic TiB2-TiC system by SHS under high gravity

Eutectic TiB₂-TiC composite ceramics were prepared by combustion synthesis under high gravity. XRD, SEM, and EDS results showed that TiB₂-TiC composites were mainly composed of the eutectic microstructures of a TiC matrix in which a large number of fine TiB₂platelet grains were dispersed uniformly; meanwhile, at the boundaries of the eutectic microstructures, discontinuously dispersed ?-carbides enriched in Ti atoms, and a few isolated irregular α-Al₂O₃ grains and Al₂O₃-ZrO₂ colonies were observed. Because high-temperature chemical reaction results in fully liquid products, the application of high gravity induces the Stocks flow in the melts, which leads to the formation of layered melts consisting of liquid Ti-Cr-C-B melt and liquid oxides. Therefore, it is considered that TiB₂-TiC composites grow through eutectic transformation far away from the equilibrium state. The results of properties measurements indicate that, with increasing mass fraction of B₄C + Ti + C in combustion systems, the relative density and fracture toughness of TiB₂-TiC composites are all among 97–99% and 6.5–7.1 MPa m^1/2, respectively, and the Vickers hardness and flexural strength are increased gradually to the maximum values of 28.6 GPa and 615 MPa, respectively. The achievement of full-density TiB₂-TiC composites benefited from the design of fully liquid SHS products and application of high-gravity field, a high hardness of the composite ceramics resulted from the absence of intermediate borides, the achievement of stoichiometric TiC phases is due to rapid solidification, whereas a high flexural strength of the composite ceramics benefited from the homogenization and refinement of the microstructures due to the rapid separation of the liquid oxides and the rapid coupled growth of TiB₂-TiC.     

Characteristics of quadruplet Ti–Mo–TiB2–TiC composites prepared by spark plasma sintering

The spark plasma sintering process was implemented to produce four different composites, namely Ti-10 wt% Mo-(0.5, 1, 2, and 4) wt% (TiB₂ + TiC). All samples were sintered at 1300 °C for 5 min under 50 MPa. A full study was carried out on the mechanical properties and the relative density of these SPSed composite samples. The best relative density of around 98.7% was related to the sample with 1 wt% (TiB₂ + TiC). The role of relative density was so predominant that the best values for all mechanical properties, i.e., bending strength, hardness, elongation, and ultimate tensile strength (UTS), were achieved for those with the highest relative density values. The formation of the in-situ TiB phase was proved by the XRD analysis. Besides, microscopical investigations (optical and SEM) showed that adding more ceramic additives led to an increased amount of porosity while Mo solubility decreased in the titanium matrix. Finally, different fracture modes on the surfaces of composite samples were studied using SEM images.     

Effect of TiB2 particles on microstructure and mechanical properties of B4C–TiB2 ceramics prepared by hot pressing

B₄C-20 wt% TiB₂ ceramics were fabricated by hot pressing B₄C and ball-milled TiB₂ powder mixtures. The effects of the TiB₂ particle size on the microstructure and mechanical properties were investigated. The results showed that the TiB₂ particle size played an important role in the mechanical properties of the B₄C–TiB₂ ceramics. In addition, SiO₂ introduced by ball milling was beneficial for densification but detrimental to the mechanical properties of the B₄C–TiB₂ ceramics. The typical values of relative density, hardness, flexural strength, and fracture toughness of the ceramics were 99.20%, 35.22 GPa, 765 MPa, and 7.69 MPa m^1/2, respectively. The toughening mechanisms of the B₄C–TiB₂ ceramics were explained by crack deflection and crack branching. In this study, the effects of high pressure and temperature caused liquefying SiO₂ to migrate to the surface of B₄C–TiB₂ and react with diffused carbon source in the graphite foil to form a 30 μm thick SiC layered structure, which improved the high-temperature oxidation resistance of the material. The unique SiC layered structure overcame the insufficient oxidation resistance of B₄C and TiB₂, thereby improving the oxidation resistance of the ceramics under high-temperature service conditions.