TiB2-based Composites Research Articles

Titanium nitrides as novel reactants for in-situ synthesis of TiB2-based composites with improved properties

A novel in-situ reactive approach based on the reactions among TiN, aluminum and boron has been developed to synthesize TiB 2 -based composites including TiB 2 - h BN (TB) and TiB 2 - h BN-AlN (TBA). Fully dense ceramics with fine-grained microstructure were successfully obtained via spark plasma sintering at 1850 °C/60 MPa/5 min. Microstructure analysis suggests h BN flakes were homogenously distributed in the TiB 2 matrix. For AlN, however, they were elongated into plate-like grains during sintering, in which lots of defects in terms of stacking faults and twinning structures were observed. The mechanical and thermophysical properties of as-sintered ceramics were comprehensively investigated and compared. Incorporating AlN significantly improved the flexure strength, hardness, fracture toughness and thermal conductivity of TiB 2 - h BN ceramics. The electrical conductivity of TB (3.06 × 10 6 S/m) is larger than that of TBA (2.35 × 10 6 S/m) at room temperature, but the value (6 × 10 5 S/m) was lower than that of TBA (6.9 × 10 5 S/m) at 1173 K. Based on the measurement of electrical and thermal conductivity, electron and phonon contributions to thermal conductivities of TB and TBA were calculated and their temperature dependences were illustrated.

Microstructure and Properties of TiB2 Composites Produced by Spark Plasma Sintering with the Addition of Ti5Si3.

Titanium diboride (TiB2) is a hard, refractory material, attractive for a number of applications, including wear-resistant machine parts and tools, but it is difficult to densify. The spark plasma sintering (SPS) method allows producing TiB2-based composites of high density with different sintering aids, among them titanium silicides. In this paper, Ti5Si3 is used as a sintering aid for the sintering of TiB2/10 wt % Ti5Si3 and TiB2/20 wt % Ti5Si3 composites at 1600 °C and 1700 °C for 10 min. The phase composition of the initial powders and produced composites was analyzed by the X-ray diffraction method using CuKα radiation. The microstructure was examined using scanning electron microscopy, accompanied by energy-dispersive spectroscopy (EDS). The hardness was determined using a diamond indenter of Vickers geometry loaded at 9.81 N. Friction–wear properties were tested in the dry sliding test in a ball-on-disc configuration, using WC as a counterpart material. The major phases present in the TiB2/Ti5Si3 composites were TiB2 and Ti5Si3. Traces of TiC were also identified. The hardness of the TiB2/Ti5Si3 composites was in the range of 1860–2056 HV1 and decreased with Ti5Si3 content, as well as the specific wear rate Wv. The coefficient of friction for the composites was in the range of 0.5–0.54, almost the same as for TiB2 sinters. The main mechanism of wear was abrasive.

Improved machinability of TiB2–TiC ceramic composites via laser-induced oxidation assisted micro-milling

Low manufacturing efficiency, poor processing controllability and deteriorated surface quality were main challenges in micro-milling high hardness TiB2-based ceramic composites. This research work investigated an innovative hybrid machining method named laser-induced oxidation assisted micro-milling (LOMM) of TiB2–TiC ceramic composites with hardness of 20 ± 0.7 GPa. Oxidation mechanism of the material under laser irradiation was studied. At single pulse energy of 0.275 mJ and scanning speed of 1 mm/s, the irradiated surface in an oxygen-rich atmosphere produced metamorphic layer including loose and porous oxide-layer as well as dense sub-layer with hardness of 9.6 ± 0.7 GPa. In addition, the main compositions of formed oxides were anatase TiO2 and rutile TiO2, which can be easily removed with an extremely low cutting force. For the investigated range of milling parameters, the milling force and the machined surface quality were studied in LOMM of TiB2–TiC ceramic composites. A significant reduction (more than 70%) of milling force during removing the oxide-layer was obtained, compared to that milling of the sub-layer. Besides, a well-machined surface quality was obtained (ap = 2 μm and fz = 0.5 μm/z) with a ductile removal mode, and surface roughness is 146 nm. As a case study, a microgroove having a width of 0.4 mm and an aspect ratio of 2.5 was fabricated successfully using LOMM. As a comparison, under identical cutting parameters conventional micro-milling (CONM) was performed. The results indicated that machined quality of the microgroove and perpendicularity of the sidewall obtained by LOMM were superior to those using CONM. Machining efficiency was also improved significantly by 106% using LOMM, compared to CONM. It confirmed that the LOMM process was an efficient and effective method to machine high hardness ceramic composites.

Effects of discrete and simultaneous addition of SiC and Si3N4 on microstructural development of TiB2 ceramics

The impact of Si3N4 and SiC additives incorporation in the microstructure and sintering behavior of TiB2-based composites were studied. Three ceramic composites including TiB2–Si3N4, TiB2–SiC, and TiB2–SiC–Si3N4 were manufactured by spark plasma sintering (SPS) at 1950 °C for 8 min under 35 MPa. The acquired ceramics were analyzed by X-ray diffractometry and scanning electron microscopy. In addition, the sintering thermodynamic was investigated using the HSC Chemistry package. X-ray diffraction patterns of the prepared ceramics revealed the in-situ formation of graphite and boron nitride in the final composites initiated from SiC and Si3N4, respectively. The thermodynamic assessments proved the role of liquid phase sintering on the sinterability enhancement of all composite samples. Field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy verified the in-situ formation of both BN and graphite components in the sample containing SiC and Si3N4 additives. Finally, the fractographical investigations clarified the transgranular breakage as the main fracture mode in the TiB2-based ceramics.

Role of co-addition of BN and SiC on microstructure of TiB2-based composites densified by SPS method

The present research aims to investigate the influences of SiC reinforcement and h-BN additive on the relative density, microstructure, and thermodynamic aspects of TiB2-based ceramics. Three different specimens, including monolithic TiB2, TiB2–SiC, and TiB2-SiC-BN were fabricated using spark plasma sintering (SPS) at 1900 °C. A dwelling time of 7 min and an external pressure of 40 MPa were applied as the sintering conditions. The characteristics of SPSed monolithic TiB2 and the prepared composites were studied using X-ray diffractometry, thermodynamic inspections, and scanning electron microscopy. These assessments unveiled the in-situ formation of TiC and graphitized carbon in the TiB2–SiC preparation process, whereas no carbon was detected in the composite doped with h-BN. Introducing SiC had immense impact on the relative density of both composites, yielding near fully dense ceramics. The intergranular type was the dominant fracture mode in the all three TiB2-based ceramics. Moreover, the addition of secondary phase substantially refined the microstructure of TiB2, reaching ceramics with finer grains than the undoped ceramic.

Effects of SiC amount and morphology on the properties of TiB2-based composites sintered by hot-pressing

This investigation intended to assess the influence of SiC morphology on the sinterability and physical-mechanical features of TiB2-SiC composites. For this aim, different volume percentages of SiC particles and SiC whiskers were introduced to TiB2 samples hot-pressed at 1950 °C for 2 h under an external pressure of 25 MPa. The characterization of as-sintered specimens was carried out using X-ray diffraction, optical microscopy, and scanning electron microscopy. The relative density studies revealed that SiCw had a more significant impact on the sinterability of TiB2-based composites. The XRD investigation confirmed the production of an in-situ TiC phase during the hot-pressing; however, some peaks related to the graphitized carbon also appeared in the patterns of SiCw-doped ceramics. The addition of 25 vol% SiCp halved the average grain size of TiB2 while introducing the same content of SiCw decreased this value by just around 20%. Finally, the highest Vickers hardness and fracture toughness were obtained for the sample reinforced with 25 vol% SiCw, standing at 29.3 GPa and 6.1 MPa m1/2, respectively.

Reactive spark plasma sintering of TiB2–SiC–TiN novel composite

The effects of adding SiC as a reinforcement and TiN as an additive on TiB2-based composites fabricated by the spark plasma sintering (SPS) technique were investigated. SPS was implemented at the sintering conditions of 1900 °C temperature, 7 min holding time and 40 MPa pressure. Adding these two secondary phases had noticeable effects on the microstructure of TiB2-based composites. A relative densities of 99.9% was obtained for TiB2–SiC–TiN composite. Detection of in-situ formed phases and investigation on them were done using SEM, XRD, EDS and thermodynamic assessment. These evaluations proved the formation of in-situ phases of TiC, BN nano-platelets, TiSi and B4C in the TiB2-based composite codoped with SiC and TiN. Formation of these in-situ phases had fascinating effects on the sinterability and ultimate microstructure of titanium diboride.

Phase evolution during spark plasma sintering of novel Si3N4-doped TiB2–SiC composite

Spark plasma sintering process was employed to fabricate TiB2–SiC and novel Si3N4-doped TiB2–SiC ceramic composites at 1900 °C for 7 min under 40 MPa. The microstructural development of TiB2-based composites was significantly influenced by the addition of SiC as a reinforcement phase and Si3N4 as a sintering aid. Thermodynamic assessment, X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy disclosed the in-situ formation of TiC, B4C and SiO2 in both samples as well as TiN and BN in the Si3N4-doped TiB2–SiC sample through the chemical reactions of SiC and Si3N4 additives with the surface oxide impurities of TiB2 particles (TiO2 and B2O3). The elimination of harmful oxide layers and the in-situ formation various secondary phases had remarkable influences on the sinterability and final microstructure of TiB2.

Effects of TiB2 particle size on the microstructure and mechanical properties of TiB2-based composites

TiB2–25 vol% (Fe-Ni) and TiB2–30 vol% (Fe-Ni) composites with different TiB2 particle size were fabricated by vacuum pressureless sintering at 1700 °C for 1 h. The influences of TiB2 particle size on the microstructure and mechanical properties was studied in detail. The phase analyses and microstructure of TiB2-based composites were investigated by X-ray diffraction, SEM, EPMA, and TEM. The experimental results showed that only TiB2 and γ(Fe, Ni) phases in the TiB2-based composites, not any other brittle phases such as M2B, M23B6 can be found. The morphology of raw TiB2 particles was irregular, however, many hexagonal crystals TiB2 grains were observed after sintering. The change of dominant fracture mode was strongly affected by the grain size of TiB2 particles, and the dominant fracture mode of TiB2-based composites transformed from trans-granular fracture to inter-granular fracture as the TiB2 particle size increasing from 1.97 to 4.27 µm. The high-toughness of TiB2-based composites was due to the synergetic action of comprehensive toughening mechanisms, including crack deflection, crack branching, as well as the strong bonding strength between TiB2 grains and γ(Fe, Ni) binder, etc. As TiB2 particle size increasing from 1.97 to 4.27 µm, the relative density, Vickers hardness, flexural strength, and fracture toughness of the TiB2-based composites decreased. The relative density, Vickers hardness, flexural strength and fracture toughness of TiB2–30 vol% (Fe-Ni) composites with the TiB2 particle size of 1.97 µm reached up to 98.20 ± 0.20%, 14.00 ± 0.40 GPa, 1000 ± 30 MPa, and 19.26 ± 0.72 MPa m1/2, respectively.

Microstructure and wear resistance of solidified TiB2-based composites for cutting tools achieved by SHS in high-gravity field

TiB2-based composites were fabricated by taking SHS with the blends of (B4C+Ti) and thermite in high-gravity field. XRD, FESEM and EDAX results showed that the composites mainly were consisted of fine plate-like TiB2, irregular TiC and (Cr,Ti)3B2 solids and Al2O3 inclusion particles. The introduction of high-gravity field brought about pure Ti-Cr-B-C liquid, whereas rapid solidification was a key factor for the achievement of fine-grained microstructures, which in turn was responsible for the much improved wear properties of the composites.

Densification improvement of spark plasma sintered TiB2-based composites with micron-, submicron- and nano-sized SiC particulates

Taguchi design of experiments methodology was used to determine the most influential spark plasma sintering (SPS) parameters on densification of TiB2–SiC ceramic composites. In this case, four processing factors (SPS temperature, soaking time, applied external pressure and SiC particle size) at three levels were examined in order to acquire the optimum conditions. The statistical analysis identified the sintering temperature as the most effective factor influencing the relative density of TiB2–SiC ceramics. A relative density of 99.5% was achieved at the optimal SPS conditions; i.e. temperature of 1800 °C, soaking time of 15 min and pressure of 30 MPa by adding 200-nm SiC particulates to the TiB2 matrix. The experimental measurements and predicted values for the relative density of composite fabricated at the optimum SPS conditions and reinforced with the proper SiC particle size were almost similar. The mechanisms of sintering and densification of spark plasma sintered TiB2–SiC composites were discussed in details.

Microstructures and mechanical properties of TiB2-based composites with self-grown carbon nanotubes synthesized using Co catalysts

Carbon nanotubes (CNTs) were grown on TiB2 powder by chemical vapor deposition using a Co catalyst. Then, the bulk CNTs(Co)-TiB2 composite was consolidated from these in-situ synthesized powder by spark plasma sintering. Homogeneously-dispersed CNTs with herringbone-like structure composed of well-crystallized graphite were observed. The flexural strength and fracture toughness of the in-situ synthesized CNTs(Co)-TiB2 composite were determined to be 987 ± 42 MPa and 12.4 ± 0.5 MPa m1/2 respectively, which were much higher than those of monolithic TiB2 and TiB2-CNTs composites synthesized by traditional ball-milling and sintering. The improvement of the composite performance was ascribed to the hybrid effect of the fully dense structure of the composite, the appropriate interfacial strength between the CNTs and the matrix, and the higher strengthening ability of well-dispersed CNTs.

Microstructure and mechanical properties of TiB2-based composites with high volume fraction of Fe-Ni additives prepared by vacuum pressureless sintering

TiB2-based composites with high volume fraction of Fe-Ni as additive were fabricated by vacuum pressureless sintering. The effect of Fe-Ni addition (Fe:Ni=6:4) at different volume fractions from 20 to 35vol% on the microstructure evolution and fracture behaviour of the TiB2-(Fe-Ni) composites was investigated. It was found that the TiB2-(Fe-Ni) composites consisted of only TiB2 and γ(Fe, Ni) phases without any brittle phases. The relative density, flexural strength and fracture toughness of the composites increased as the Fe-Ni content increased. The results indicated that the TiB2–35vol% (Fe-Ni) composites exhibited the optimum combination of physical and mechanical properties, i.e., the relative density of 98.32%, the Vickers hardness of 8.56GPa, the flexural strength of 1050.92MPa and the fracture toughness of 17.75MPam1/2. The high fracture toughness of the TiB2–35vol% (Fe-Ni) composite was due to an intensive coupled mechanism of the near-full density, dimple fracture of Fe-Ni phase, crack deflection, crack bridging, grain's pull-out and transgranular fracture of the TiB2 particles.

Characterization of hot pressed SiC whisker reinforced TiB2 based composites

TiB2–SiC ceramic composites, with different contents of SiC whiskers (SiCw), as a ceramic sinter-additive, were prepared by the hot pressing process at 1850°C for 2h under a pressure of 20MPa. For comparison, a monolithic TiB2 ceramic was also fabricated under the identical temperature, pressure, atmosphere, and holding time by the hot pressing process. The effects of fabrication process and SiC whiskers on microstructural features, phase evolution and mechanical properties were investigated. Hardness measurements revealed an initial increase in hardness for TiB2–SiC compared to TiB2. Also the improvement of the fracture toughness was attributed to the toughening and strengthening effects of SiC whiskers such as crack deflection. The results showed that promoted densification of TiB2–SiC ceramic composites is due to addition of SiC whiskers and reduction of oxide impurities by reacting with SiC whiskers and removing them from the surface layer of TiB2 particles. The reaction between TiB2 particles and SiC whiskers led to in-situ formation of TiC phase in the matrix as well. In general, it is concluded that the sinterability of TiB2-based composites was remarkably improved by introducing SiC whiskers compared to the single phase TiB2 ceramic.

Hypervelocity impact of TiB2-based composites as front bumpers for space shield applications

Based on the typical Whipple-type shield, a novel shield configuration with a front bumper of TiB2-based composite is designed in this paper, and the hypervelocity impact tests are conducted to compare the protection performance of this new composite bumper with that of the conventional aluminum bumper at the predicted impact velocities of about 3km/s, 5km/s and 7km/s. The protection efficiency of different bumper materials is evaluated by the bumper perforation as well as the damage pattern of the rear wall and the witness plate. The postmortem observations of macroscopic and microscopic damage morphology reveal that the TiB2-based composite bumper can diminish the damage to the rear wall and exhibits better protective performance than the aluminum bumper, especially when the impact velocity reaches 5km/s or more. Analyses of the shadowgraph of debris indicate that the kinetic energy of debris cloud is distributed among a large number of ultrafine particles, therefore, the well-fractured projectile fragment and widespread impact area can be taken as the main reasons for the better performance of TiB2-based composite bumpers. Besides, preliminary researches demonstrate some positive application of this new bumper material in protective systems for micrometeoroid and orbital debris shielding.

Microstructure, Densification and Mechanical Properties of TiB<sub>2</sub>-TiC-NiAl Ceramic-Based Composite

By adjusting mass fraction of Ni-Al composite additive in Ti-B4C primary system, a series of TiB2-based ceramic composites were prepared by combustion synthesis in high gravity field. Because the adiabatic temperature of the whole reaction system maintained a constant in the presence of mass fraction of Ni-Al additive smaller than 18.55%, increasing mass fraction of Ni-Al additive to be 15% brought about the improved homogeneity in refined microstructure of the enhanced-densification TiB2-based composite, so flexural strength and fracture toughness of the ceramic composite increased simultaneously due to the enhanced self-toughening mechanisms contributed by a number of fine TiB2 platelets.

Effect of sintering temperature on the mechanical properties and microstructure of carbon nanotubes toughened TiB2 ceramics densified by spark plasma sintering

TiB2-based composites containing 15vol% multi-walled carbon nanotubes were synthetized at the temperature of 1600°C to 1800°C for 10min under a uniaxial load of 20MPa by spark plasma sintering. Microstructure, mechanical properties and densification behavior of the composites were studied. It was shown that mechanical properties were increased by introduction of carbon nanotubes, especially for the fracture toughness. The fracture toughness was ∼9.1MPam1/2, which was much higher than that of monolithic TiB2 ceramics. The dense microstructure was the primary factor to improve the mechanical properties. The toughening mechanisms were crack deflection and carbon nanotubes pull-out. The results presented here provide a potential method for improving the fracture toughness of TiB2 ceramics.

Influence of silicon carbide addition on the microstructural development of hot pressed zirconium and titanium diborides

The influences of adding SiC on the microstructure and densification behavior of ZrB2 and TiB2 ceramics, hot pressed at 1850°C for 60min under 20MPa, were investigated. The sintered samples were characterized by SEM, EDS and XRD methods. A fully dense TiB2-based ceramic was obtained by adding 30vol% SiC. The grain size of ZrB2 or TiB2 matrices in the final microstructures decreased with increasing SiC content. The XRD analyses, microstructural characterization as well as thermodynamical calculations proved the in-situ formation of TiC in the SiC reinforced TiB2-based composites. The interfaces between ZrB2 and SiC grains in the SiC reinforced ZrB2-based composites were free of any impurities or tertiary interfacial phases such as ZrC. This result was consistent with the X-ray diffraction pattern and thermodynamics.

Microstructural development and mechanical properties of hot pressed SiC reinforced TiB2 based composite

The present work is focused on investigating the effect of SiC addition (0, 15, 20, 25 and 30vol.%) on microstructural features, phase evolution and mechanical properties of the vacuum hot pressed TiB2 at 1850°C/2h/20MPa. Hardness measurements revealed an initial increase in hardness from 14.2GPa for nominally pure TiB2 to 20.8GPa for TiB2–15vol.% SiC and a subsequent decrease with further increase in the SiC addition. Also the TiB2–30vol.% SiC showed an improved indentation fracture toughness of 5.76MPam1/2 which was mostly attributed to the addition of the SiC particles that could activate toughening mechanisms such as crack deflection, crack branching and grain breaking. The microstructure of the sintered samples was characterized by XRD and FESEM, which indicated that SiC reacted with and removed oxide impurities (TiO2 and B2O3) that were present on the particle surfaces. Elimination of such impurities promoted densification by minimizing grain coarsening and in composite contain 30vol.% SiC the reaction led to in situ formation of TiC. Hence, the results indicated that sinterability of TiB2-based composites was remarkably improved by addition of SiC compared to the single phase TiB2 ceramic.

Bulk TiB₂-Based Ceramic Composites with Improved Mechanical Property Using Fe-Ni-Ti-Al as a Sintering Aid.

The densification behavior, microstructure and mechanical properties of bulk TiB2-based ceramic composites, fabricated using the spark plasma sintering (SPS) technique with elements of (Fe–Ni–Ti–Al) sinter-aid were investigated. Comparing the change of shrinkage displacement of pure TiB2 and TiB2–5 wt% (Fe–Ni–Ti–Al), the addition of elements Fe–Ni–Ti–Al into TiB2 can facilitate sintering of the TiB2 ceramics. As the sintering temperature exceeds 1300 °C, the relative density does not significantly change. Alumina particles and austenite (Fe–Ni–Ti) metallic binder distributed homogeneously in the grain boundary of TiB2 can inhibit the growth of the TiB2 grains when the sintering temperature is below 1300 °C. The density and particle size of TiB2 greatly influence the mechanical behavior of TiB2–5 wt% (Fe–Ni–Ti–Al) composites. The specimen sintered at 1300 has the highest microhardness of 21.1 ± 0.1 GPa with an elastic modulus of 461.4 GPa. The content of secondary borides (M2B, being M = Fe, Ni), which are more brittle than TiB2 particles, can also influence the fracture toughness. The specimen sintered at 1500 °C has the highest fracture toughness of 6.16 ± 0.30 MPa·m1/2 with the smallest M2B phase. The results obtained provide insight into fabrication of ceramic composites with improved mechanical property.