TiB2 Reinforcement Research Articles

Three-dimensional microstructural characterization of discontinuously reinforced Ti64–TiB composites produced via blended elemental powder metallurgy

Three-dimensional (3D) microstructures of TiB reinforcement in two discontinuously reinforced Ti–6Al–4V (Ti64) alloy composites produced via blended elemental (BE) powder metallurgy are reconstructed from large-area high-resolution optical montage serial sections. The TiB phase in both composites shows whisker morphology with roughly hexagonal cross-sections, a unimodal size distribution, and uniform random morphological orientations. The TiB whiskers in these composites are significantly coarser compared to similar materials produced via pre-alloyed powder metallurgy but did not contain coarse primary TiB particles.

In Situ Synthesis of TiB<sub>2</sub>/Mg Composites by Flux-Assisted Synthesis Reaction of the Al-Ti-B System in Molten Magnesium

TiB2 particulate reinforced magnesium matrix composites were successfully fabricated by adding a TiB2–Al master alloy processed via the flux-assisted synthesis (FAS) reaction into molten magnesium. X-ray diffraction (XRD) analysis and microstructural characterization of the TiB2–Al master alloy revealed the formation and uniform distribution of TiB2 reinforcements. By stirring, magnesium matrix composites with dispersed homogenously TiB2 particles can be obtained. Microstructural characterization of the TiB2/Mg composites revealed retention of hexagonal or rectangular TiB2 particulates with the size of about 1 μm.

Corrosion Behavior of Al‐based Composites Containing In‐situ TiB2, Al2O3 and Al3Ti Reinforcements in Aerated 3.5 % Sodium Chloride Solution

Corrosion behavior of aluminum based composites containing in-situ TiB2, Al2O3 and Al3Ti reinforcements in aerated 3.5% sodium chloride solution was investigated. The composites were prepared from the Al-TiO2-B system via reactive hot pressing. Polarization measurements showed that the composite containing high Al3Ti content (CA) exhibits higher corrosion current density than the composite containing a trace amount of Al3Ti phase (CB). Microstructural examination revealed that the pits were initiated at fractured Al3Ti blocks.

Oxidation Behavior of In Situ-Synthesized (TiB+TiC)/Ti6242 Composites

The oxidation behaviors of TiB and TiC particle-reinforced, titanium-matrix composites (TMCs) were studied in air at 550–650°C, The oxidation kinetics follow approximately a parabolic rate law. The oxidation rates, which were lower than those of Ti6242, decrease gradually as oxidation proceeds. The oxide scales formed on TMCs were predominantly rutile and α-Al2O3. No B2O3 and other oxides were observed within the oxide scale. The in situ-synthesized TiB and TiC reinforcements can increase the oxidation resistance of TMCs. The oxide scales that formed exhibited excellent spallation resistance under all testing conditions. No scale cracking or spallation could be observed, implying that growth and thermal stresses generated during heating and cooling have been effectively released. The mechanisms of the decrease in oxidation rate and the improvement on spallation resistance are discussed based on microstructure studies.

In-Situ Synthesis of Metal Matrix Composite Coating with Laser Melting-Solidifying Processes

In order to improve wear resistance of titanium alloy, with pre-placed B4C and NiCrBSi powders on Ti-6Al-4V substrate, a process of laser melting-solidifying metal matrix composite coating was studied. The coating was examined using XRD, SEM and EDS. A good metal matrix composite coating was obtained in a proper laser process. There is a metallurgical interface bonding between the coating and the substrate. During laser melting-solidifying process, high energy of laser melted the pre-placed powders and a part of Ti-6Al-4V substrate, which made Ti extend into a melting pool. A reaction between Ti and B4C took place in the melting pool, which in-situ synthesized TiB2 and TiC reinforcements in the coating. The composite coating mainly consists of γ-Ni matrix, TiB2, TiC and CrB reinforcements. Microstructure of the reinforcements obtained using the laser melting-solidifying is not as same as that of reinforcements obtained using general producing methods. Due to high cooling rate of the melting pool, TiC nucleated primarily and grew up in dendrite morphology from undercooled liquid. Encircling TiC, TiB2 precipitated later and grew up in hexagonal prism morphology. TiC and TiB2 formed an inlaid microstructure.

Microstructure and mechanical behavior of AlSiCuMgNi piston alloys reinforced with TiB2 particles

AlSiCuMgNi piston composites reinforced with in-situ TiB2 particles were fabricated by mixing salts reaction process successfully. Microstructures of the composites were observed by mean of scanning electron microscope (SEM) and transmission electron microscope (TEM). X-ray diffraction (XRD) was used to identify the phases in the composites. TiB2 reinforcement grows in equiaxed or near equiaxed shape and the interfaces between reinforcements and matrix are clear. Compared with the matrix alloys, the composites show an obvious aging peak and an incubation time in the hardness. The aging is accelerated in the composites reinforced with TiB2. At room temperature, the ultimate tensile strength (UTS) of the composites increases as the percentage of TiB2 reinforcement increases. When the temperature is beyond 250°C, the ultimate tensile strength of the piston composites decreases sharply. The fracture surfaces of the piston composites are analyzed.

In Situ TiB Reinforced Titanium Metal Matrix Composites Prepared by Spark Plasma Sintering

In situ synthesized TiB reinforced titanium matrix composites of Ti-B and Ti-TiB2 systems have been prepared by spark plasma sintering at 800-1200 °C under 20 MPa for 5 min. The effects of sintering temperature and reinforcement volume fraction on flexural strength, Young’s modulus and fracture toughness of the composites were investigated. The in situ synthesized TiB reinforcements are randomly and uniformly distributed in titanium matrix. The TiB whiskers are aligned along [010] direction, and the crystallographic planes of the TiB needles are always of the type (100), (101) and (10 1) . The parallel TiB were observed in β-Ti grains in both of the investigated composites. The in situ TiB needle is likely to grow along [010] direction which is parallel to [111] direction of cubic lattice of β-Ti phase.

Laser Cladding Ni-Base Composite Coating on Titanium Alloy with Pre-Placed B4C+NiCoCrAlY

Using a CO2 laser, a process of cladding Ni-base composite coating on Ti6Al4V with pre-placed B4C and NiCoCrAlY was studied. A good metallurgical bonding coating without cracks and pores was obtained in reasonable ratios of components and low energy laser process. Morphology and microstructure of the coating were analyzed with OM, XRD, SEM and EDS. It is certain that there was a reaction between B4C and Ti during in-situ producing TiB2 and TiC. The Ni-base composite coating is strengthened with TiB2 and TiC reinforcement phases. Vickers Hardness Tester measured that the average microhardness of the coating is HV1200 and it is 3.5 times of the Ti6Al4V substrate. The high hard coating containing several reinforcement phases greatly enhances wear resistance of titanium alloy.

Microstructural Characterization of Spark Plasma Sintered <I>In Situ</I> TiB Reinforced Ti Matrix Composite by EBSD and TEM

The spark plasma sintered in situ TiB reinforced titanium metal matrix composite was investigated by EBSD and TEM. The sintered composite consists of 30.8% α-Ti phase, 55.7% β-Ti phase and 12.9% in situ TiB reinforcements. Most of the TiB whiskers distributed along phase boundaries between α-Ti and β-Ti, others located within α-Ti and β-Ti grains. Some β-Ti grains with parallel TiB whiskers were observed in the orientation imaging micrograph (OIM). The TiB grows along [010] direction and forms whisker with a hexagonal cross-section. The [010] direction of paralleled TiB whiskers is parallel to [111] direction of cubic β-Ti. High density stacking faults are formed in (100) T i B planes to minimizing the lattice mismatch between TiB and the Ti matrix.

Microstructure and mechanical properties of in situ TiB reinforced titanium matrix composites based on Ti–FeMo–B prepared by spark plasma sintering

The in situ synthesized TiB reinforced titanium matrix composites have been prepared by spark plasma sintering at 800–1200 °C under 20 MPa for 5 min. The effects of sintering temperature and reinforcement volume fraction on flexural strength, Young’s modulus and fracture toughness of the composites are investigated. The titanium matrix consists of α-Ti and β-Ti phases, and the volume fraction of β-Ti increases with increasing sintering temperatures. The in situ synthesized TiB reinforcements are distributed randomly and uniformly in matrix. The transverse section of TiB has a hexagonal shape aligned along [0 1 0] direction, and the crystallographic planes of the TiB needles are always of the type ( 1 0 0 ) , ( 1 0 1 ) and ( 1 0 1 ¯ ) . The 10 vol% TiB reinforced composite sintered at 1000 °C exhibits excellent mechanical properties. The flexural strength, Young’s modulus and fracture toughness of this composite are 1560 MPa, 137 GPa and 8.64 MPa · m 1/2, respectively.

Effect of Double Reinforcements on Elevated‐Temperature Strength and Toughness of Molybdenum Disilicide

Flexural strength and fracture toughness of molybdenum disilicide and its composites with 10 wt% TiB2 and 10 wt% TiB2+ 10 wt% SiC, synthesized by the hot‐pressing technique, were evaluated as a function of temperature, ranging from ambient temperature to 1600°C. Results show that the composites have higher strength and slightly lower toughness as compared with monolithic MoSi2 at room temperature. At high temperatures, the composites exhibit higher strength as well as higher toughness vis‐à‐vis monolithic MoSi2. Among the composites, the double reinforcement of SiC and TiB2 was found to be more effective in improving the mechanical properties. A transition from brittle to ductile behavior was observed at temperatures greater than 1300°C for all materials tested. The high‐temperature mechanical behavior was found to be significantly influenced by the flow of an intergranular glassy phase and the attendant cavity nucleation and growth along the grain boundaries. Micromechanisms responsible for the ambient as well as the elevated‐temperature property improvement in composites are discussed with the aid of fractography.

Oxidation Behavior of <i>In Situ</i> Synthesized TiB/Ti Composite in Air Environment

Isothermal oxidation behavior of in situ synthesized TiB/Ti composites has been investigated. Samples of titanium matrix composites reinforced with 0, 5 and 8 vol% TiB particulates were oxidized at 823, 873, and 923 K for 300 h in atmospheric air. Scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry, and transmission electron microscopy (TEM) were used to identify oxidation products and characterize oxide scale morphology. Oxidation was observed to follow parabolic kinetics. Rate of oxidation decreased with the increase of TiB reinforcements. The oxide scale formed on TiB/Ti composites was rutile-type TiO2. No other oxides were observed within the oxide scale. The increased oxidation resistance due to the addition of the in situ synthesized TiB reinforcement was attributed to the improved tendency for the formation of thin and dense oxide avoiding crack and spallation, the strong enough interfacial cohesion and the clean interfacial microstructure between the reinforcements and the titanium matrix alloy.

Mechanical properties of Ti-6Al-4V/TiB composites with randomly oriented and aligned TiB reinforcements

In situ Ti-6Al-4V/TiB discontinuously reinforced composites, containing 20 and 40% of TiB whiskers by volume, were produced by blending Ti, Al/V, and TiB 2 powders. The consolidated powder blends were annealed to transform the TiB 2 particles to TiB. The microstructural evolution of the composite was studied as a function of heat treatment duration at 1100, 1200, 1300 and 1400 °C. The mechanical properties of Ti-6Al-4V/TiB composites were established in tension and compression at room temperature and 300 °C, and by resonant ultrasound spectroscopy (RUS), for the two volume fractions of TiB, and for randomly oriented and aligned arrays of TiB whiskers. The average Young’s modulus of the composite with 20% of randomly oriented TiB whiskers was 153 GPa, compared to 109 GPa for unreinforced Ti-6Al-4V. The average Young’s modulus of composites with 20 and 40% of aligned TiB whiskers was measured along the extrusion axis as 169 and 205 GPa, respectively. The stiffness of TiB whiskers was determined from bulk measurements with the Halpin-Tsai equation to be 482 GPa. Yield and ultimate strengths near 1200 MPa were measured. The strength and ductility of the materials were limited in the present study by non-optimal matrix microstructure and inadequate particulate distribution, and approaches for properties improvements are provided.

Investigation of the Young's modulus of TiB needles in situ produced in titanium matrix composite

In situ Ti/TiB composites with different volume fractions of discontinuous TiB reinforcements were produced by powder metallurgy. After compacting Ti+TiB 2 powders by hot unidirectional pressure, heat treatments led to the in situ formation of distinctive needles of TiB, randomly distributed in the titanium matrix. The Young's modulus of TiB was evaluated using the ASW computation method and experimental Vickers micro-indentation. Three point bend tests were performed on Ti/TiB composites as a function of the TiB volume fraction in order to extract the Young's modulus of TiB from the elastic properties of the composite. The different values obtained according to these three methods were discussed and compared with the literature.

Preparation of Ti-TiB-TiC & Ti-TiB composites by in-situ reaction hot pressing

Discontinuously reinforced Titanium matrix composites, with TiB and TiC reinforcements, have been produced by the reaction hot pressing process. Powder metallurgy approach has been adopted with two different starting powder mixtures, namely Ti+TiB2 and Ti+B4C, the former leading to a composite with only TiB reinforcement, while the latter resulted in a combination of TiB+TiC reinforcement. The initial composition was adjusted in such a way as to have a reinforcement content of 70% by volume, the rest being matrix titanium. The X-ray diffraction analysis confirmed the completion of reaction and the scanning electron microscope studies revealed the morphology of the reinforcement. The effect of morphology and reinforcement type on mechanical properties was evaluated with hardness measurement and 3-point bend tests. It is concluded that the composite with the TiB+TiC reinforcement has a better strength and toughness, due to the presence of needle shaped TiB, while the composite with only TiB reinforcement in the form of TiB particulate has inferior strength and fracture resistance.

Densification and compressive strength ofin-situ processed Ti/TiB composites by powder metallurgy

In the present study, the densification of Ti/TiB composites, the growth behavior ofin-situ formed TiB reinforcement, the effects of processing variables — such as reactant powder (TiB2, B4C), sintering temperature and time — on the microstructures and the mechanical properties ofin-situ processed Ti/TiB composites have been investigated. Mixtures of TiB2 or B4C powder with pure titanium powder were compacted and presintered at 700°C for 1 hr followed by sintering at 900, 1000, 1100, 1200, and 1300°C, respectively, for 3hrs. Some specimens were sintered at 1000°C for various times in order to study the formation behavior of TiB reinforcementin-situ formed within the pure Ti matrix. TiB reinforcements were formed through different mechanisms, such as the formation of fine TiB and the formation of coarse TiB by Ostwald ripening or the coalescence of fine TiB. There was no crystallographic relationship between TiB reinforcement and the matrix. There were voids at the interface between the TiB reinforcement and the Ti matrix due to the preferential growth of coarse TiB without a particular crystallographic relationship with pure Ti matrix and the surface energy between the Ti matrix and TiB reinforcements. Therefore, the densification of Ti/TiB2 compacts was hindered by the preferential growth of coarse TiB reinforcements. The mechanical properties ofin-situ processed composites were evaluated by measuring the compressive yield strength at ambient and high temperatures. The compressive yield strength of thein situ processed composites was higher than that of the Ti-6A1-4V alloy. It was also found that the compressive yield strength of the composite made from TiB2 reactant powder was higher than that of the composite made from B4C at the same volume fraction of reinforcement. A crack path examination suggested that the bonding nature of interface between matrix and reinforcement made from TiB2 reactant powder was better than that made from B4C.

Microstructure and Mechanical Properties of Ti-B-N Cast Alloys Prepared by Reactive Arc-Melting

Ti-B-N cast alloys were prepared by a reactive arc-melting technique using elemental titanium and boron nitride powders. The alloys obtained were composites of titanium matrix containing nitrogen of 3 mol% or less and a small amount of TiB reinforcement. The microstructure of the matrix was a cellular structure consisting of elongated dislocation cells with 1-2 μm in width and 5-10 μm in length, for Ti-1B-1N alloy. The TiB particles were rod-like in shape with size of less than 0.5 μm in diameter and agglomerated to form clusters along the grain boundary. The mechanical properties were mainly dependent on the content of nitrogen and the influence of TiB on the mechanical properties was relatively small. The Ti-B-N cast alloys containing suitable concentration of nitrogen, Ti-0.58-0.5N alloys, had a high strength of 920 MPa with adequate ductility of more than 5%.

Microstructure and tensile properties of mechanically alloyed Ti–6A1–4V with boron additions

Particulate titanium metal matrix composites (MMCs) offer advantages for a wide range of structural applications with increases in stiffness and possibly wear resistance. A powder metallurgy/mechanical alloy route was used successfully to give a fine, uniform distribution of boron in titanium alloy powder. This powder was hot isostatically pressed and during the process TiB reinforcement was formed by an in-situ reaction. Significant tensile ductility in MA titanium alloy (without boron), equivalent to wrought material was achieved, along with good tensile strength. In materials with high TiB volume fractions it is thought that the fine boride size and high strength matrix caused embrittlement. This suggests that the use of a lower strength matrix, such as commercial purity titanium, and shorter milling times would provide a better balance of strength, stiffness and ductility for this type of composite.

Effect of densification and TiB2 reinforcement on the wear of molybdenum disilicide

Wear tests were done in a pin-on-disc machine by sliding MoSi2 pins against hard-steel discs in a normal load range of 5-140 N and a speed of 0.5 m/s under nominally dry conditions in the ambient. The specific wear rate of the pin undergoes two transitions: severe to mild at low load and mild to severe at high load. The mild-wear domain is distinguished by the formation of a protective mechanically mixed layer of steel and its oxides, transferred from the counterface in particulate form. Increasing the hardness by densification and TiB2 reinforcement lowers the specific wear rate and expands the mild-wear load domain. However, even when the volume wear rate is normalised with respect to the real contact area (load/hardness) the non-dimensional wear factor is still seen to decrease with densification and reinforcement. This indicates that fracture toughness may also play an important role in determining the wear-resistance of these materials. The surface coverage on the pin by the mechanically mixed layer increases with densification and reinforcement.

Microstructural stability, microhardness and oxidation behaviour of in situ reinforced Ti–8.5Al–1B–1Si (wt%)

Microstructural stability, microhardness and oxidation behaviour of an in situ reinforced Ti–8.5Al–1B–1Si (wt%) alloy was examined in both air and argon environments. When exposed for up to 5760 min at temperatures below the α/α+α2 transius, hardening occurred in both air and argon environments. The increase in hardness in the air heat-treated samples is attributed to a combination of solid-solution strengthening due to the oxygen and the precipitation of the α2 phase, while the increase in hardness in the argon heat-treated samples is primarily due to the precipitation of the α2 phase. On the other hand, when heat treated above the α/α+α2 transius, after an initial increase in hardness there is a drop in hardness which is attributed due to elimination of the α2 phase and a decreased contribution of boron and silicon in the matrix towards the solid-solution strengthening by virtue of coarsening of the TiSi2 and TiB reinforcements. Oxidation of the alloys follows a parabolic oxidation law when oxidized both in an environment of flowing air and static air with the primary oxidation product being TiO2. The activation energy for oxidation is 200 kJ mol-1 in an environment of flowing air and 303 kJ mol-1 in static air. The difference in activation energy arises from the difference in the availability of oxygen at the reaction front in the two cases. © 1998 Chapman & Hall