TiB2 Powders Research Articles

W – TiB2 Composite Material for Electro-spark Deposition

The W – TiB2 composite materials were prepared by spark plasma sintering at INM Gliwice, Poland and by solar powder metallurgy at Plataforma Solar de Almeria (PSA), Spain. Composites were prepared by sintering of green compacts of W powder with 60 vol.% of TiB2 powder. During the spark plasma sintering the sintering temperature was 1800 °C, pressure of 22kN, time of 300 s and heating rate of 1.67 °C/s. In solar furnace the sintering temperature was 1820 °C, pressure less, time 600 s and heating rate of 2.33 °C/s. The resulting composites prepared by spark plasma sintering possess 95 - 97 % of theoretical density. The composites prepared in solar furnace have porosity of 49%. Both composites are brittle and prone to cracking. The following phases were observed by EDS and XRD analyses: After solar sintering only W and TiB2 phases were observed. After spark plasma sintering WB and TiB2 phases were observed. The reason is different method of preparation. Finally it was proved experimentally that both composites can be successfully used as electrodes for electro spark deposition of hard wear resistant layers on metallic substrates.

Influence of the milling process on TiB2 particle reinforced Al-7 wt.-% Si matrix composites

Abstract Al-Si metal matrix composites have generally been manufactured using casting methods. Powder metallurgy has been used as an alternative manufacturing technique to obtain more homogeneous and segregation-free products. In this study, 2 wt.-% TiB2 particle reinforced Al-7 wt.-% Si composites were manufactured using high energy ball milling, cold pressing (at 450 MPa) and pressureless sintering (at 570 °C for 2 h under Ar flow) techniques. The effects of different milling processes, such as mechanical alloying at room temperature and/or cryomilling in an isolated polycarbonate cylinder soaked in liquid nitrogen or sequential milling, on the Al-7 wt.-% Si-2 wt.-% TiB2 powders and corresponding bulk products were investigated. The microstructural, physical and mechanical properties of the composites sintered from the mechanically alloyed, mechanically alloyed and cryomilled, and sequentially milled powders were significantly improved as compared with those of as-blended ones. The highest density, the highest microhardness and the lowest wear rate were obtained in a composite sintered from mechanically alloyed and cryomilled powders at 92.38 %, 214.14 ± 41.17 HV and 3.8 × 10−3 mm3·N−1 × m−1, respectively.

Effect of Plastic Deformation on the Structure and Properties of the Ti/TiB Composite Produced by Spark Plasma Sintering

A Ti/17 vol % TiB composite material is produced by spark plasma sintering of a mixture of titanium and 10 wt % TiB2 powders at a temperature of 1000°C. Multiaxial isothermal forging is performed at t = 850°C to enhance the mechanical properties of the composite. Deformation develops dynamic recrystallization in the titanium matrix and shortens TiB whisker crystals by a factor of ~3. Multiaxial isothermal deformation decreases the temperature of the brittle-to-ductile transition of the Ti/TiB composite material by ~200°C (from ~500 to ~300°C) and results in a plasticity of ~5% upon compression at room temperature. Deformation decreases the microhardness and the wear resistance to a certain degree. Multiaxial isothermal deformation weakly changes the corrosion properties of the composite material in comparison with the initial state.

Electroless nickel-boron coating on B4C-Nano TiB2 composite powders

B4C-TiB2 nanocomposites have high hardness of boron carbide and high strength and toughness of titanium diboride. One of the most important problems in adding TiB2 powder to B4C powder is its lack of uniform distribution in the final powder, so in this research we have tried to synthesis B4C-Nano TiB2 composite powder by sol gel method. Also, since coating by electroless method has been introduced as an effective way to improve the homogeneity and sinterability of ceramic composites containing a small amount of metal phase, the surface of B4C-Nano TiB2 composite powder is coated by electroless nickel-boron plating and the effect of C2H8N2 complexing agent at temperatures of 75, 85and 95 °C and pH 13 is examined. Scanning electron microscope equipped with EDS analyzer for investigation of microstructure and morphology of coated B4C powder and X-ray diffraction to determine the composition and phases were used. The results indicate that the calcination temperature of 1200 °C and 60 min duration is quite appropriate for the synthesis of B4C-Nano TiB2 composite powder. It was also found that in the electroless coating process, the amount of the C2H8N2 complexing agent in the plating bath has significant effect on the quantity of coating and uniformity of it on the surface of the B4C particles. By increasing the amount of C2H8N2 in the electroless plating bath in each of the temperatures 75, 85 and 95 °C, the nickel-boron coating is reduced. The highest amount of nickel-boron coating was achieved on the surface of B4C-Nano TiB2 composite powder at 95 °C and the nickel salt to complexing agent ratio of 1: 6 (20.55 g/l).

Microstructure Characterization of <i>In Situ</i> Ti-TiB Metal Matrix Composites Prepared by Powder Metallurgy Process

Metal matrix composites (MMCs) are the new generation materials that combine both the metallic properties (ductility and toughness) and ceramic characteristics (high strength and modulus), leading to higher strength in shear and compression, at higher service temperatures. Titanium matrix composites possess light weight, high strength and good corrosion resistance and are used as structural materials in automobiles and aerospace industries. In the present study, in situ Ti-TiB composites were fabricated by reinforcing (2, 5, 10 and 20 wt. %) TiB2 powder (mean size <10 microns) into titanium powder (mean particle size ~26.58 μm) and subsequently consolidated by vacuum sintering at 1300 °C for 3 h. X-ray diffraction, scanning electron microscopy (SEM) and density measurements were carried out to characterize the prepared composites. The results showed that all compositions led to high density composites, and the hardness of the composites increased with an increase in the amount of reinforcement. The mechanism of vacuum sintering is yet to be understood in the consolidation of composites and the detailed evolution of microstructure needs to be analysed.

Study of Ignition of High-Energy Materials with Boron and Aluminum and Titanium Diborides

This paper describes the ignition of high-energy materials (HEMs) on the basis of ammonium perchlorate and ammonium nitrate and an energetic binder, containing the powders of Al (base composition), B, AlB2, AlB12, and TiB2, upon initiation of the process by a CO2 laser in the heat flux density range of 90–200 W/cm2. The ignition delay time and surface temperature of the reaction layer during the heating and ignition of HEMs in air are determined. It is obtained that the complete replacement of a micron-sized aluminum powder by amorphous boron in the composition of HEMs significantly reduces the ignition delay time of the sample (by 2.2–2.8 times) with the same heat flux density, and this occurs due to the high chemical activity of and difference between the mechanisms of oxidation of boron particles. The use of aluminum diboride in HEMs reduces the ignition delay time by 1.7–2.2 times in comparison with the base composition. The ignition delay time of the HEM sample with titanium diboride decreases slightly (by 10–25%) relative to the ignition delay time of the base composition.

Fabrication of stainless steel 316L/TiB2 composite coating via friction surfacing

Stainless steel 316L/TiB2 composite coatings were fabricated with different TiB2 contents using friction surfacing (FS) on the stainless steel 304 substrate. One or two blind holes were drilled at different positions axially on the cylindrical 316L consumable rods for keeping micron-size TiB2 powder as the reinforcement in the coatings. After FS, TiB2 was found to be embedded into the austenitic matrix and also partially decomposed leading to the formation of FeB2 and FeTi under high temperature and high strain rate. Compared with the friction-surfaced (FSed) 316L coating, the grain size of austenite in the TiB2 reinforced composite coating was refined from 7.8 to 0.64 μm, where austenite grains closed to {111} tends to transform to FeTi. Compared with monolithic 316L coating, the hardness of the FSed 316L/TiB2 coating was significantly increased from 219 to 1056 HV0.2 owing to the presence of TiB2 and intermetallic phases, finer austenitic grains and higher misorientation density. The pitting corrosion resistance of the FSed 316L coating was improved due to the elimination of MnS inclusions whereas the FSed 316L/TiB2 coating possessed lower pitting resistance due to the presence of FeTi. Moreover, the passivity of the 316L/TiB2 coating in 3.5% NaCl solution was preserved but the capability of re-passivation was degraded.

Effects of TiB2 Particle and Short Fiber Sizes on the Microstructure and Properties of TiB2-Reinforced Composite Coatings

In this study, particle and short fiber-reinforced titanium matrix composite coatings are prepared via laser in situ technique using (0.5 and 50 μm) TiB2 and Ti powder as cladding materials. The microstructure and properties of the composite coatings are studied, and the changing mechanism of the microstructure is discussed. The results reveal that particle agglomeration is prone to appear with using fine TiB2 particles. Decomposition of the particles preferentially occurs with using coarse TiB2 particles. The cracks and pores on the surface of the coating are formed at a lower laser energy density. With the increase in the laser energy density, cracking on the surface of the coating diminishes, but the coating exhibits depression behavior. The depression extent of the coating using fine TiB2 particle as the reinforcement is much less than that of the coating using coarse TiB2 particle. Moreover, the size of the aggregate and the tendency of cracking can be reduced with the increase in Ti addition. Meanwhile, short TiB fiber bundles are formed by the diffusion mechanism of rod aggregate, and randomly oriented TiB short fibers are formed mainly by the dissolution–precipitation mechanism of fine TiB2 particles. Moreover, the growth of short TiB fibers can be in an alternating manner between B27 and Bf structures. The micro-hardness and wear resistance of the coatings are evidently higher than that of the titanium alloy substrate. The wear resistance of the large size TiB2 coating is higher than that of the small size TiB2 coating under the condition of low load.

Effects of synthesis temperature and Fe catalyst amount on the performance of in situ CNTs/TiB2 composites

Carbon nanotubes (CNTs) were synthesized in situ over TiB2 powders by using a Fe catalyst at temperatures ranging from 800 °C to 1000 °C. The CNT(Fe)–TiB2 composites were then successfully consolidated by spark plasma sintering. Results indicated that CNT(Fe)–TiB2 composites with 20 wt% Fe sintered at 1400 °C for 5 min provided the optimal combination of dense microstructures and excellent properties. These properties included the following: relative density, 97.3%; flexural strength, 985 ± 48 MPa; and fracture toughness, 11.8 ± 0.4 MPa m1/2. Retention of the perfect structure and homogenous dispersion at the molecular level of CNTs in TiB2 matrix were identified as the main factors that contribute to the marked improvement of the mechanical properties of the composites.

Pressureless sintering of TiB2 with low concentration of Co binder to achieve enhanced mechanical properties

This paper studies the pressureless sintering of TiB2 based materials with a low concentration of 3 wt% Co binder to result in enhanced mechanical properties. Utilizing ultra-fine TiB2 powders obtained from a special carbon coated precursors method, TiB2-3 wt% Co composite can be densified to a relative density of ~98.6% at a temperature of 1500 °C without external pressure, which is over ~200 °C lower than literature reported temperatures. The Co binder partially reacts with TiB2 and converts into Co2B and Ti-B-Co with good wettings with TiB2. Due to the low sintering temperature, the microstructure is fine with a grain size of ~1.75 ± 0.16 µm. The sample also combines superior mechanical properties including Vickers hardness of ~28.4 ± 0.6 GPa, elastic modulus of ~519.6 ± 17.2 GPa, indentation fracture toughness of ~7.0 ± 0.4 MPa√m, and flexural strength of ~638.3 ± 34.9 MPa. The variation of the Co content to 1, 10, or 20 wt% either leads to low relative density (~91.5% for 1 wt% Co even at a temperature of 1600 °C) or deteriorated mechanical properties (the combination of hardness and fracture toughness, for samples containing 10 and 20 wt% Co) due to the formation of significant amount of brittle Co2B. Correlations between mechanical properties and microstructure are further discussed.

Microstructure and mechanical properties of hot pressed submicron TiB2 powders

This paper studies the microstructure and mechanical properties of hot pressed submicron TiB2 powders obtained from a special carbon coated precursors method. With the hot press temperature increasing from 1500 °C to 1800 °C, the relative density increases and the sample maintains a single TiB2 phase. The powders are able to be sintered to a relative density of ~94.5% at the temperature of 1800 °C. For the first time, unique elongated platelike grain structure, which has only been observed from transient liquid phase or reaction sintered borides, also forms at the sintering temperature of 1800 °C. In addition, the sample sintered at 1800 °C has a fine microstructure (elongated grain of ~0.3–3 µm) and high mechanical properties (hardness of ~27.6 ± 2.3 GPa, flexural strength of ~560 ± 49 MPa, and fracture toughness of ~6.5 ± 0.2 MPa m−1/2). Correlations between mechanical properties and microstructure are further discussed.

Microstructures and mechanical properties of B4C-TiB2-SiC composites fabricated by ball milling and hot pressing

B4C-TiB2-SiC composites were fabricated via hot pressing using ball milled B4C, TiB2, and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84 GPa, 858 MPa and 8.21 MPa m1/2, respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B4C-TiB2-SiC composite.

Study on Mechanical Alloying of TiB<sub>2</sub> Particulate Reinforced Titanium Matrix Composites

TiB2 particulate reinforced titanium matrix composites were prepared by mechanical alloying and spark plasma sintering. Volume fraction of TiB2 powders in the composites are 5%, 10%, 15%. The effect of milling time and the volume fraction of reinforcement on microstructure and properties of the composites were studied. The results show that with increasing milling time, the size of powder particles decreases, quantity of them increases, and microstructure of the sintered samples becomes finer and more uniform. When milling time reaches 30h, the trend of powder agglomeration increases, the downward trend of the particle size becomes slowly. With the milling time, the density of titanium matrix composites is on the rise. The density of 10vol%TiB2 particulate reinforced titanium matrix composites can reach 4.799 g/cm3, with 30h milling time and sintering at 900°C. The density and hardness of the composites increase with increasing the volume fraction of TiB2. When the volume fraction of TiB2 is 15%, after milling 10h and sintered at 800°C, the density and hardness of the composites can reach 4.713g/cm3 and HV851.58.

Preparation and sintering of ultrafine TiB2 powders

Ultrafine TiB2 powders were synthesized by carbon/boron thermal reduction method and single-phase TiB2 ceramics were prepared by hot pressing the obtained TiB2 powders with Y3Al5O12 (YAG) as sintering additive. Phase and morphologies of powders were characterized by XRD, SEM and TEM. XRD and SEM were used to investigate phase and microstructure of sintered samples. Results indicated the synthesized powders to be ultrafine and the better materials to be obtained for 5wt% YAG content, that showed the best sintering behavior leading to relative density, hardness, flexural strength and fracture toughness of 99.1%, 49.3GPa, 607MPa and 12.68MPam1/2, respectively.

Effect of High-Pressure Torsion on Structure and Microhardness of Ti/TiB Metal–Matrix Composite

Effect of high-pressure torsion (HPT) at 400 °C on microstructure and microhardness of a Ti/TiB metal–matrix composite was studied. The starting material was produced by spark plasma sintering of a mixture of a pure Ti and TiB2 (10 wt %) powders at 1000 °C. The microstructure evolution during HPT was associated with an increase in dislocation density and substructure development that resulted in a gradual microstructure refinement of the Ti matrix and shortening/redistribution of TiB whiskers. After five revolutions, a nanostructure with (sub) grain size of ~30 nm was produced in Ti matrix. The microhardness increased with strain attaining the value ~520 HV after five revolutions. The contribution of different hardening mechanisms into the hardness of the Ti/TiB metal–matrix composite was quantitatively analyzed.

A corrosion mechanism of titanium diboride in KF−AlF3−Al2O3 melt

TiB2 samples were exposed to molten KF−AlF3−Al2O3: 54.8-42.1-3.1mol% salt, at 680°C for 50, 100 and 200h. The corroded samples of TiB2 were investigated by SEM-EDX, EBSD, XRD, FT-IR and MAS NMR analysis. Corrosion was noted to occur predominantly as pitting attacks on the surface of the investigated materials. An inter-crystal and trans-crystal corrosion were identified on the cross-sections of the samples. A perturbation of TiB bonds was detected (SEM-EDX and NMR analysis), at which a formation of orthorhombic TiO2 was also identified (EBSD analysis). The subsequent NMR, XRD and FT-IR analysis of the behaviour of TiB2 powder in molten KF−AlF3−Al2O3 supports the statement about the formation of orthorhombic TiO2 and mullite type of aluminium borates.

Microstructural characterization and mechanical properties of TiB2 reinforced Al6061 matrix composites produced using stir casting process

Particulate reinforced aluminum matrix composites are the most promising alternative for applications where the combination of high strength and ductility is essential. In the present study, Al-TiB2 composites with different amounts of reinforcement (3, 6 and 9wt%) were fabricated using stir casting method. after optimizing the process parameters such as preheating temperature, stirring speed and duration. Microstructure, mechanical properties and the fracture surfaces of tensile specimens were studied. Optical microstructure of prepared composites showed a uniform distribution of reinforcements in matrix and also SEM analysis demonstrated the strong bonding between matrix and reinforcements which is the consequence of improved wettability due to K2TiF6 addition and preheating of TiB2 powder before adding to the melt. In addition to microstructure uniformity, the tensile strength of composites was improved with increasing the volume fraction of TiB2 reinforcement particles without any significant decrease in elongation. SEM micrographs from fractured surfaces of tensile specimens approved that the ductile fracture is occurred in Al6061 alloy in all of prepared composites through nucleation and coalescence of micro-voids.

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.

Effect of phenol formaldehyde resin on the carbothermal synthesis of TiB2

The effect of phenol formaldehyde resin (PFR) on the preparation of TiB2 powders by carbothermal synthesis at temperatures (T) of up to 1670 K has been studied by simultaneous thermal analysis. Unlike in the case of dynamic heating, under isothermal conditions (1570 K, 3 h) the addition of PFR increases the product yield by 13%. The formation of carbon black as a result of PFR thermolysis is favorable for the formation of titanium carbide, from which TiB2 is synthesized.

Synthesis and characterization of in-situ CNTs reinforced TiB2-based composite by CVD using Ni catalysts

In-situ synthesized Carbon nanotubes-(Ni)-TiB2 (CNTs(Ni)-TiB2) composite powders were produced by chemical vapor deposition. The effect of the synthesis temperature (700–1100°C) on the growth of the CNTs was investigated. The bulk CNTs(Ni)-TiB2 composites were consolidated from the as-prepared powders by spark plasma sintering at 1500–1700°C. The results showed that the highest flexural strength and fracture toughness of the CNTs(Ni)-TiB2 composite were obtained when it was synthesized at 1000°C and then sintered at 1600°C, which were determined to be 1182 ± 53MPa and 15.8 ± 0.4MPam1/2, respectively. These superior properties were attributed to the dense microstructures, well-dispersed CNTs and the strong interfacial strength between the CNTs and the TiB2 powders. The fracture mode was a mixed mode, including transgranular and intergranular modes. The CNTs debonding and pull-out were thought to be effective strengthening mechanisms to exhaust the fracture energy.