TiB2 Composites Research Articles

Machinability, Modelling and Statistical Analysis of In-Situ Al–Si–TiB2 Composites

Aluminum and its alloys have numerous applications in manufacturing, aerospace, and automotive industries. At elevated temperatures, they start to fail in fulfilling their roles and functions. Aluminum-based metal matrix composites (MMCs) are good alternatives for metal and alloys due to their excellent properties. However, the conventional machining of several composites shows complications for a number of reasons, such as high tool wear, poor surface roughness, high machining cost, cutting forces, etc. Numerous studies have already been conducted on the machinability of various MMCs, but the machinability of Al–Si–TiB2 composite is still not well studied. It is of utmost importance that several process parameters of conventional machining are precisely controlled as well as optimized. In this study an effort was made to optimize input parameters such as cutting speed, depth of cut, and feed to obtain well-finished final components with the minimum cutting force and tool wear. These progressions are involved with multiple response characteristics, therefore the exploration of an appropriate multi-objective optimization technique was indeed essential. The performance characteristics of cutting forces and surface roughness were considered for optimization of the machining parameters. Analysis of variance (ANOVA) was employed for the optimization and statistical analysis.

Effect of FeNiCrBSiC–MeB2 Material Composition on the Oxidation Behavior at High Temperatures

The effect of TiB2 and CrB2 additives on the oxidation behavior of composites made of the NiCrBSiC and FeNiCrBSiC self-fluxing alloys has been studied in air at temperatures to 800°C. It is found that the FeNiCrBSiC–20 wt.% TiB2 composite is oxidized most intensively. Oxidation occurs selectively: titanium diboride is oxidized at 450–550°C to form TiO2 and B2O3, and self-fluxing alloy components are oxidized at 570–730°C.

Multi-layered structures of Ti-6Al-4V alloy and TiC and TiB composites on its base fabricated using blended elemental powder metallurgy

Due to the high specific strength of titanium, materials on its base are contemplated as a viable alternative in low-weight armor production. However, when the armor parts are fabricated using traditional and costly ingot and wrought technology, the feasibility of implementation is questionable. Proposed cost-efficient process of fabrication uses blended elemental powder metallurgy (BEPM). Multi-layered structures based on Ti-6Al-4 V alloy and its metal-matrix composites (MMC) with 5–10% (vol.) of TiC and TiB were fabricated and tested. Relatively large multi-layered plates and bars with TiC composite were successfully sintered due to very close shrinkage values of the alloy and composite. Shrinkage values of TiB composites were substantially lower than those for alloy, what led to delamination of layered structures, cracking and distortion of the plates. The difference in shrinkage behavior between the ML plates with TiC vs. TiB MMCs was explained by the difference in the ways those two types of reinforcement particles evolve within the structures. We have shown that by the optimization of the powder size and hydrogen content in BEPM process the shrinkage mismatch of the layered structures could be effectively nullified.

Tensile Fracture of TiB Whisker Reinforced Ti Alloy Matrix Composites

TiB whisker reinforced Ti alloy matrix (Ti–TiB) composites have attracted attention as the aerospace materials with their high specific mechanical properties for long time. However, strengthening mechanism of Ti–TiB composites has not been revealed because of the agglomeration and incomplete precipitation of TiB whiskers in the Ti alloy matrix yet. In this study, we addressed to fabricate fully-dense TiB whisker reinforced Ti-6Al-4V alloy matrix (Ti6Al4V–TiB) composites via powder metallurgical process, which have the microstructure to discuss their tensile properties with the theories for composite materials. The Young’s modulus and ultimate tensile strength of Ti6Al4V–10 vol% TiB composite were 130 GPa and 1193 MPa, respectively. Note that the elongation of Ti6Al4V–10 vol% TiB composite was approximately 2.8 % although the elongations of Ti–TiB composite have been reported are few (; less than 1%) due to the agglomeration of TiB whiskers in Ti matrix.

HIGH TEMPERATURE TRIBOLOGICAL BEHAVIOR OF STIR-CAST Al–TiB2 METAL MATRIX COMPOSITES

This study considers high temperature tribological behavior of Al-TiB2 aluminum matrix composites (AMCs) fabricated through stir cast method. Effect of operating temperature on wear and friction behavior is studied for four different weight percentages of reinforcements using a high-temperature tribo-tester over a temperature range of 50[Formula: see text]C–250[Formula: see text]C under normal load in the range of 25–75[Formula: see text]N. Surface morphology and wear debris are studied through scanning electron microscopy (SEM) images. Energy dispersive X-ray (EDAX) and X-ray diffraction (XRD) studies are performed to observe the wear mechanism at high temperature. Increase in the amount of reinforcement improves wear resistance of composites at all temperatures. Friction and rate of wear are found to increase with operating temperature. Formation of oxide layers and softening of the surface are found to play crucial role in controlling the tribological behavior of stir cast Al–TiB2 composites at high operating temperatures.

Microstructure–mechanical properties correlation in spark plasma sintered Ti–4.8 wt.% TiB2 composites

Abstract Ti TiB2 composites were fabricated from powder mixtures via spark plasma sintering method. Mechanical behavior of the sintered composites were then investigated via both routine and nanoindentation methods. Results indicated a significant increase in ultimate tensile strength and hardness of the composite, when the sintering temperature is raised. Besides common increase in the relative density of the composite, such a behavior was also attributed to the higher amounts of in-situ formed TiB whiskers. The remarkable reduction in bending strength is probably due to limited formability of unreacted coarse TiB2 particles and agglomerated in-situ formed phases. Such findings were then discussed in detail, based on the nanomechanical behavior of the primary and in-situ formed phases in Ti TiB2 composite sintered at 1200 °C. It was concluded that the superiority of mechanical properties in the mentioned sample may be due to high strength primary and in-situ formed reinforcements distributed homogenously in the matrix. Such reinforcement also provided high strength interfaces, according to interfacial nanoindentation approaches.

Conductive TiB2–AlN–BN-Based Composite SHS Ceramics

The structure, phase composition, and electrical conductivity of TiB2–AlN–BN-based ceramics fabricated by self-propagating high-temperature synthesis (SHS) are investigated. The temperature dependence of the specific electrical conductivity was measured in range T = 300–1300 K in vacuum of 2 × 10–3 Pa according to the standard four-probe dc-current procedure. It is established that the TiN and BN contents in the synthesis products increase while those of TiB2 and Al decrease with an increase in the TiB2 content in the initial mixture from 60 to 80 wt % and a decrease in the Al concentration from 40 to 20 wt % because of the reaction of TiB2 with nitrogen. A decrease in the Al concentration in the initial mixture leads to a decrease in the AlN content in the synthesis products. The results showed the mismatch of electrical resistance curves ρ(T) during the heating–cooling cycle for all ceramics compositions, which is associated with the variation in the length of the contact zone of conducting phases in range T = 800–1200 K. Three characteristic temperature regions are found: (I) from 300 to 800 K, when ρ monotonically increases with an increase in temperature; herewith, heating and cooling ρ(T) curves coincide completely; (II) the behavior of electrical resistance varies at T = 800–1200 K—its values depend strongly on the heat treatment mode of the sample; and (III) heating–cooling curves coincide completely at T > 1200 K.

Microstructure, mechanical, and tribological properties of pressureless sintered and spark plasma sintered Fe TiB2 nanocomposites

Abstract In this work, microstructure, mechanical and tribological properties of Fe TiB2 sintered from in-situ nanocomposite powders were investigated. TiB2 particles in pressureless sintered (PLS) specimen were found to be as large as several μm while those in spark plasma sintered (SPS) specimen were about 5 nm. Mechanical and tribological properties of the SPS specimen were superior than those of the PLS specimen, which may be due to the formation of the fine TiB2 particles. It was further noted that Fe TiB2 composites were fragmented into particulate wear debris, resulting in a film formation that could suppress wear progression. The outcomes of this work may be useful to better understand mechanical and tribological properties of Fe TiB2 nanocomposites, associated with the structures.

Characterization of TiB2-AlN composites for application as cutting tool

Densified ceramic TiB2-AlN composites were prepared by spark plasma sintering and samples were subjected to short time machining tests. The maximum relative density and toughness were 96.9% and 16.2GPa, respectively. Composites with 70wt% AlN and 70wt% TiB2 were applied as cutting tools and tested for cutting parameters. Scanning electron microscopy (SEM) allowed the analysis of the microstructure and the wear surfaces after cutting tests. The 70% TiB2 composites revealed unsatisfactory performance while the 70wt% AlN disclosed satisfactory cutting performance.

Effects of B4C particle size on the microstructures and mechanical properties of hot-pressed B4C–TiB2 composites

Full dense B4C–30 vol% TiB2 composites were prepared by hot pressing at 2000 °C under 35 MPa from four different starting B4C powders with their medium particle sizes ranging from 0.5 to 35.8 µm. The effects of B4C particle size on the microstructures and mechanical properties of composites were investigated. The results indicated that both B4C and TiB2 grains grew during sintering process, and each kind of grains had a pinning effect on the grain growth of the other. With coarse B4C powders as raw materials, TiB2 grains in obtained B4C–TiB2 composites tended to grow with the [001] zone axis parallel to the applied pressure direction, which possibly reinforced the composites. When the particle size of the starting B4C powder was 7.09 µm, the obtained B4C–TiB2 composite exhibited the optimized mechanical properties including a flexural strength of 754 MPa, a Vicker hardness of 30.01 GPa and a fracture toughness of 5.23 MPa m1/2, respectively, due to the most homogenous and finest microstructures.

Microstructure and Mechanical Properties of In Situ TiB/TiC Particle-Reinforced Ti-5Al-5Mo-5V-3Cr Composites Synthesized by Spark Plasma Sintering

In situ TiB and TiC particle-reinforced titanium matrix composites (TMCs) based on a near-β Ti-5Al-5Mo-5V-3Cr alloy (Ti-5553) reacting chemically with B4C were processed by spark plasma sintering (SPS). The influence of powder milling parameters (low-energy mixing or high-energy milling) on the chemical reaction behavior between the matrix and the B4C particles during sintering was investigated. Taking the microstructure into account, characterization of the particle strengthening effect was carried out under compressive loading conditions. High-energy milling resulted in a significantly higher degree of B4C conversion during sintering. This was attributed to plastic deformation of the initial matrix powder and more homogeneous distribution of the B4C particles accompanied by a significant reduction in cluster formation. In comparison to the unreinforced Ti-5553 matrix, the hardness, stiffness, and compressive strength of the TMCs were successfully increased due to particle reinforcement. The powder milling treatment improved these properties further—a phenomenon directly associated with the higher degree of B4C conversion. Instead of the expected formation of stoichiometric TiC, the formation of nonstoichiometric TiC1−x with x ≈ 0.5 was observed. Molybdenum, vanadium, and chromium formed a solid solution in TiB and TiC1−x. Additionally, the titanium content in the matrix particles was markedly reduced, while the aluminum content roughly doubled.

Studies on Porosity of Al-4.5%Cu-2.5pTiB<sub>2</sub> <i>In Situ</i> Composites

In the present paper, experimental investigation as well as computer assisted casting simulation technique is used to analyse the effect of different parameters like properties of sand and molding methods to predict defects in green sand casting. An attempt has been made to obtain the optimal settings of the moulding sand and mould related process parameters for the casting of Al-4.5%Cu-2.5TiB2 composites. The green sand related process parameters considered in the study are moisture content, green compressive strength, permeability of moulding sand and mould hardness. In the fabrication of composites, porosity is greatly influenced due to improper gating/riser system design. The analysis of porosity is performed using Auto-CAST simulation technique by the introduction of a new gating system designed and the solid model was developed for sand mould cavity. A number of iterations using Auto-CAST simulation software were performed for mould filling and solidification analysis to reduce the level and intensities of porosities in cast Al-4.5%Cu-2.5TiB2 composite. With new gating and feeding system design, reduction in porosity and improvement in yield is observed. The simulation results were found to be in good agreement when compared with the experimental trial.

An Experimental and Modeling Study of Synthesis, Consolidation and Aging Behavior of AA2014 Composite Reinforced by TiB2 via Powder Metallurgy Method

Aluminum 2014 alloy composite reinforced with TiB2 particulates with different volume% of TiB2 (5, 10 and 15%) has been successfully synthesized by P/M route. The composite powders were consolidated by cold uniaxial compaction pressure followed by sintering at 590 °C in N2 atmosphere. The Al 2014–TiB2 composites were aged at 160 °C between 0 and 8 h followed by microstructural characterization and hardness evaluation. Scheil cooling and equilibrium calculations were performed using FactSage for qualitative understanding of the microstructural evolution during sintering and aging operations. In addition, the thermo-physical properties such as hardness, density and transverse rupture strength of the sintered samples were evaluated.

Electrically Conducting Ceramics Based on Al–AlN–TiB2

The high-temperature conductivity of ceramics based on Al–AlN–TiB2 obtained by self-propagating high-temperature synthesis has been studied. The dependences of DC resistivity were measured in vacuum (1 Pa) by a four-point technique in a temperature range of 293–1273 K. The evolution of the phase composition of the material upon heating was studied by time-resolved diffraction in real-time mode. The measurements show a “metallic” behavior of conductivity when the Al–AlN–TiB2 composite is heated, and there is also an abrupt change of resistivity in a temperature range of 870–970 K that is linked with Al melting. In this case, the crystalline structure of ceramic phases does not undergo changes in the studied temperature range. The same temperature coefficient of resistance has been observed for all studied compositions up to the melting point of aluminum.

Production and Properties of B4C–TiB2 Composites with Isotropic Eutectic Microstructure

Directionally reinforced B4C–TiB2 eutectic alloys were produced from green powder compacts by floating zone melting. Their mechanical properties were studied over a wide range of temperatures (25–1600°C). The high-temperature strength of the reinforced B4C–TiB2 composites hardly changes with increasing temperature and reaches about 200 MPa at 1600°C. Mechanical grinding and subsequent spark plasma sintering were used to produce reinforced B4C–TiB2 composites with an isotropic eutectic microstructure. The microstructure of the bulk-reinforced ceramic samples was examined. The developed ceramics meet the requirements imposed on high-temperature creepresistant and oxidation-resistant materials for reusable hypersonic vehicles.

CONDUCTIVE TIB2–ALN–BN-BASED COMPOSITE SHS CERAMICS

The paper studies the microstructure, phase composition, and electrical conductivity of TiB2–AlN–BN-based composite ceramics obtained by self-propagating high-temperature synthesis (SHS). Electrical resistivity dependence on temperature was measured in the range Т = 300÷1300 K in a vacuum of 2·10–3 Pa using a standard 4-point DC technique. It is found that higher TiB2 content in the initial composition (from 60 to 80 wt.%) and lower Al content (from 20 to 40 wt.%) results in increased TiN and BN content in synthesis products, and decreased TiB2 and AlN content as a result of TiB2 reaction with nitrogen. Lower Al content in the initial mixture leads to lower AlN content in synthesis products. According to the results obtained, electrical resistivity curves are inconsistent during the «heating–cooling» cycle for all ceramic compositions due to changes in the contact zone of conducting phases in the temperature range Т = 800÷1200 К. Three specific temperature ranges were identified: (I) 300 to 800 K when ρ values increase monotonically with increasing temperature, while heating and cooling ρ(Т) curves coincide completely; (II) Т = 800÷1200 К when electrical resistivity behavior varies – its values strongly depend on the sample heat treatment mode; (III) Т > 1200 К, when coincidence of heating-cooling curves is observed.

Synthesis and Characterization of Electrically Conductive Silicone Rubber – TiB2 Composites

Abstract Electrically conductive composites comprised of silicone rubber and titanium diboride (TiB2) were synthesized by conventional mixing methods. Fine particles of TiB2 (in micron size) and 10 parts per hundred parts of rubber (phr) proportion of carbon black (XC-72) were used to make the composites with HTV silicone rubber. The composites were cured at appropriate temperature and pressure and the effect on the electrical properties was studied. The resistance of the silicone rubber is ~ 1015Ω which decreases to 1 – 2 kΩ in case of composites with negligible effect of heat ageing. The hardness increases by ~ 35% simultaneous to the decrease of ~ 47% in the tensile strength. Morphological characterization indicates the homogeneous dispersion of the fillers in the composite.

Synthesis and properties of conductive B4C ceramic composites with TiB2 grain network

AbstractHigh electrical resistance and low fracture toughness of B4C ceramics are 2 of the primary challenges for further machining of B4C ceramics. This report illustrates that these 2 challenges can be overcome simultaneously using core‐shell B4C‐TiB2&TiC powder composites, which were prepared by molten‐salt method using B4C (10 ± 0.6 μm) and Ti powders as raw materials without co‐ball milling. Finally, the near completely dense (98%) B4C‐TiB2 interlayer ceramic composites were successfully fabricated by subsequent pulsed electric current sintering (PECS). The uniform conductive coating on the surface of B4C particles improved the mass transport by electro‐migration in PECS and thus enhanced the sinterability of the composites at a comparatively low temperature of 1700°C. The mechanical, electrical and thermal properties of the ceramic composites were investigated. The interconnected conductive TiB2 phase at the grain boundary of B4C significantly improved the properties of B4C‐TiB2 ceramic composites: in the case of B4C‐29.8 vol% TiB2 composite, the fracture toughness of 4.38 MPa·m1/2, the electrical conductivity of 4.06 × 105 S/m, and a high thermal conductivity of 33 W/mK were achieved.

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.

A novel functionally gradient Ti/TiB/TiC hybrid composite with wear resistant surface layer

Ti/TiB/TiC hybrid composite was processed by a novel one-step in-situ process using spark plasma sintering (SPS). KBF4, which was used as a boron precursor for the first time, reacted with Ti to form the TiB reinforcement insitu. Graphite foils were used on either side of the compact as a carbon source to produce TiC during sintering. Ti reacted with carbon and formed TiC on both the surfaces of the composite. The thickness of the TiC layer was found to be ∼50 μm. The microstructure of the composite was graded with ultrafine TiC on top, fine needles of TiB near the surface and coarser TiB whisker reinforced Ti (Ti-4Al-2Fe/TiBw) in the bulk. The grain size of Ti also varied from 1 μm near the surface to 12 μm in the bulk. The surface layer exhibited very high hardness to the tune of 20 GPa compared to 7 GPa of the bulk Ti-4Al-2Fe/TiB composite. The functionally gradient composite exhibited only mild wear with wear rate that was almost one order of magnitude lower than that of the bulk Ti-4Al-2Fe/TiBw composite. While there were abrasive grooves formed on the Ti-4Al-2Fe/TiB bulk composite, the hybrid composite showed almost nil wear damage under the same test conditions. The surface TiC layer thus acted as an effective protection against wear and tear.