Ti TiB Research Articles

In situ synthesis of TiB whisker reinforcements in the joints of Al2O3/TC4 during brazing

Al2O3 ceramic has been successfully joined to Ti–6Al–4V alloy with Ag–Cu–Ti–B mixed powder. The TiB whiskers in the brazing layer were in situ synthesized during brazing. The effects of B content in reactant on the phase composition, microstructure and shear strength of the joints were investigated using SEM, EDS, and shear test. Results indicate that B content in the filler has a great impact upon the microstructure of the joints via exerting an influence on the volume fraction of in situ synthesized TiB whiskers. When the TiB content is 40vol.%, the shear strength reaches the maximum value of 77.9MPa. The higher content of TiB (≥40vol.%) depresses the shear strength of the joints due to the interfacial thermal stress cannot be relaxed. Reaction phases (Ti3Cu2AlO, Ti2Cu, Ti2(Cu, Al), Ti(Cu, Al) and Ti3Al) appear in the joint, moreover, as the volume fraction of TiB increase, Ag (s.s) and Ti(Cu, Al) distribute more uniform and fine in the brazing layer, as well as TiB whiskers mainly distribute in them. Eventually, Ti3Cu2AlO, TiB and TiB2 firstly generate based on the thermodynamic analysis, and in excessive Ti circumstances, TiB whiskers remain in the brazing alloy.

In situ reaction synthesis of Ti–TiB composites containing high volume fraction of TiB by spark plasma sintering process

The in situ toughened Ti–TiB ceramic–matrix composites containing high volume fraction of TiB were synthesized by spark plasma sintering technique under a pressure of 50 MPa, with sintering temperature ranging from 1100 °C to 1400 °C and heating rate of 150 °C/min, using Ti and TiB 2 powders. Results indicated that Ti–TiB composites sintered at 1400 °C provided the optimal combination of dense microstructure, well developed lath-shaped TiB grains, and excellent mechanical properties, including the relative density of 99.6%, bending strength of 608 MPa, and a rather high fracture toughness of 9.35 MPa m 1/2. Moreover, the micro-hardness of the composites reaches a relatively high level (18.3 GPa).

Wear-resistant Ti–B–N nanocomposite coatings synthesized by reactive cathodic arc evaporation

Abstract Wear-resistant Ti–B–N coatings have been synthesized by reactive arc evaporation of Ti–TiB 2 compound cathodes in a commercial Oerlikon Balzers Rapid Coating System. Owing to the strong non-equilibrium conditions of the deposition method, a TiN–TiB x phase mixture is observed at low N 2 partial pressures, as determined by elastic recoil detection analysis, X-ray diffraction, X-ray spectroscopy, transmission electron microscopy and selected area electron diffraction. The indicated formation of a metastable solid solution of B in face-centered cubic TiN gives rise to a maximum in hardness (>40 GPa) and wear resistance on the expense of increased compressive stresses. A further saturation of the nitrogen content results in the formation of a TiN–BN nanocomposite, where the BN phase fraction was tailored by the target composition (Ti/B ratio of 5/3 and 5/1). However, the amorphous nature of the BN phase does not support self-lubricious properties, showing friction coefficients of 0.7 ± 0.1 against alumina. The effect of an increased bias voltage on structure and morphology was investigated from −20 to −140 V and the thermal stability assessed in Ar and air by simultaneous thermal analysis up to 1400 °C.

A microstructure and sonic fatigue investigation of Ti–TiB functionally graded materials

The microstructure and high-cycle sonic fatigue behavior of 3- and 25-mm-thick titanium–titanium boride (Ti–TiB) functionally graded plates were evaluated. The TiB content had a significant effect on the microstructure. A needle-like TiB phase existed at low TiB phase volume percentages (< 33.8%), while higher volume percentages resulted in TiB-phase clustering. For larger layer thicknesses, the transition or interface region between the layers was more evident. Fracture surface images of the fatigue specimens indicated that high TiB content regions exhibited brittle fracture characteristics while the Ti-rich layers exhibited ductile failure characteristics. A Ti–85%TiB alloy was also investigated and this material exhibited TiB clustering and sporadic fatigue lives as well as brittle fracture characteristics.

Spark plasma sintering and deformation of Ti–TiB 2 composites

Spark plasma sintering (SPS) was used to investigate the densification and deformation behaviour of Ti–TiB 2 composites. Fully densified samples were prepared with Ti addition larger than 5%. The prepared composites can be deformed under compression at 1700 °C to achieve a strain of 50% without cracking. At lower temperatures, cracks were initiated due to low ductility of TiB 2 and low content of Ti. During the sintering and deformation, TiB is formed via a reaction between Ti and TiB 2. To elucidate the formation mechanism of TiB in the SPS process, reactive sintering of TiB using element precursors was also performed. Fully dense samples were prepared but it was not possible to prepare pure uniphase TiB. The reactive sintering resulted in the formation of TiB and TiB 2 mixtures at low temperatures and a mixture of TiB 2 and Ti 3B 4 at high temperature.

The Application of Self-Propagating High-Temperature Synthesis of Engineered Porous Composite Biomedical Materials

The term “self-propagating high-temperature synthesis” (SHS), or “combustion synthesis”, refers to an exothermic chemical reaction process that utilizes the heat generated by the exothermic reaction to ignite and sustain a propagating combustion wave through the reactants to produce the desired product(s). The products of combustion synthesis normally are extremely porous: Typically 50 percent of theoretical density. Advantages of combustion synthesis over traditional processing routes, e.g., sintering, in the production of advanced materials such as ceramics, intermetallic compounds and composites include process economics, simplicity of operation, and low energy requirements. However, the high exothermicity and rapid combustion propagation rates necessitate a high degree of control of these reactions. One research area being conducted in the Center for Space Resources (ISR) at the Colorado School of Mines (CSM) is the application of SHS to synthesize advanced, engineered porous TiB–Ti, NiTi, NiTi–TiC, TiC–Ti, and multiphase/heterogeneous calcium phosphate (HCaP) for bone tissue engineering and drug delivery systems. Processing conditions, such as reaction stoichiometry, green density, and gasifying agent, greatly affect the structure and properties of the SHS porous products. In general, all porous composite materials produced in this work for tissue engineering, including NiTi, NiTi + TiC, TiC + Ti, TiB + Ti, and multiphase/heterogeneous calcium phosphate (HCaP), appear to be biocompatible with no overt toxicity observed either in vitro or in vivo. An example of an SHS reaction is Ni + Ti = NiTi. The extent of the porosity and the size of the pores can be controlled using certain ‘gasifying agent' such as B2O3, CaCO3. The article discusses the synthesis of porous TiB–Ti, NiTi, Ni3Ti–TiC, TiC–Ti, and multiphase/heterogeneous calcium phosphate (HCaP) for bone tissue engineering and drug delivery systems.

Processing and properties of titanium–titanium boride (TiBw) matrix composites—a review

Although titanium (Ti) alloys possess desirable properties such as specific strength, corrosion resistance and low density, their low specific stiffness and wear resistance have restricted their widespread application. Recently, composite strategies have provided means for overcoming these limitations. Titanium boride (TiBw) in-situ whisker reinforcements are currently recognized as one of the most compatible and effective reinforcements for Ti. This paper provides an overview of recent activities in this evolving area of Ti–TiB composites, covering processing, properties and potential applications.

Grid indentation analysis of composite microstructure and mechanics: Principles and validation

Several composites comprise material phases that cannot be recapitulated ex situ, including calcium silicate hydrates in cementitous materials, hydroxyapatite in bone, and clay agglomerates in geomaterials. This requirement for in situ synthesis and characterization of chemically complex phases obviates conventional mechanical testing of large specimens representative of these material components. Current advances in experimental micro and nanomechanics have afforded new opportunities to explore and understand the effect of thermochemical environments on the microstructural and mechanical characteristics of naturally occurring material composites. Here, we propose a straightforward application of instrumented indentation to extract the in situ elastic properties of individual components and to image the connectivity among these phases in composites. This approach relies on a large array of nano to microscale contact experiments and the statistical analysis of the resulting data. Provided that the maximum indentation depth is chosen carefully, this method has the potential of extracting elastic properties of the indented phase which are minimally affected by the surrounding medium. An estimate of the limiting indentation depth is provided by asssuming a layered, thin film geometry. The proposed methodology is tested on a “model” composite material, a titanium-titanium monoboride (Ti–TiB) of various volumetric proportions. The elastic properties, volume fractions, and morphological arrangement of the two phases are recovered. These results demonstrate the information required for any micromechanical model that would predict composition-based mechanical performance of a given composite material.

Nanostructured two-phase nc-TiN/a-(TiB 2, BN) nanocomposite thin films

Thin films of Ti–B–N with different N contents were deposited on Si(1 0 0) at room temperature by reactive unbalanced close-field dc-magnetron sputtering using three Ti targets and one TiB 2 target in an Ar–N 2 gas mixture. The effect of N content on bonding structure, microstructure, phase configuration, surface roughness and mechanical properties have been investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cross-sectional scanning electron microscopy (SEM), plan-view and cross-sectional high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and microindentation measurements. It was found that the N content significantly affected phase segregation and microstructure. The nitrogen-free TiB 0.65 films showed an amorphous compound consisting of Ti and TiB 2 (Ti–TiB 2). After adding about 28 at.% N, Ti was preferentially bonded to N to form TiN, accompanying with formation of small amounts of TiB and BN bonds. At this stage they combined TiB 2 to form a two-phase nanocomposite with microstructures comprising of nanocrystalline (nc-) TiN phase in nitrogen-containing amorphous (a-) TiB 2 matrix. Addition of more N promoted formation of BN bonding at cost of TiB 2, which resulted in formation of nanocomposite nc-TiN/a-(TiB 2, BN) thin films. A small grain less than 8 nm in size was found at low N content, and the grain size increased with increasing N content. A low microhardness value of about 20 GPa was obtained in the amorphous Ti–TiB 2 compound, and a maximum microhardness value of about 50 GPa was achieved in nc-TiN/a-TiB 2. A decrease of microhardness took place after formation of BN (i.e. amorphous matrix composed by both TiB 2 and BN) with further increasing N content, and a hardness value of about 35 GPa was followed at high N contents. The surface roughness strongly depended on the phase configuration. The higher the mole fraction of nanocrystalline TiN phase, the rougher the surface became.

Effects of nitrogen content on nanostructure evolution, mechanical behaviors and thermal stability in Ti–B–N thin films

Several thin films of Ti–B–N with different N contents were deposited at 500 °C on Si (100) substrate by reactive unbalanced dc magnetron sputtering, followed by vacuum annealed at 600, 800 and 1000 °C, respectively. The effect of nitrogen content on microstructure, mechanical behaviors and thermal stability was investigated by X-ray diffraction (XRD), plan-view high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) and microindentation methods. The results indicated that nitrogen content had a great effect on phase configuration, microstructure and the corresponding mechanical behaviors. An amorphous (a-) Ti–TiB 2 compound thin film which consists of Ti and TiB 2 with a low hardness value was formed without nitrogen doped. Addition of small amount of nitrogen (10 at.% N in this study) produced nanocomposite nanocrystalline (nc-) Ti(N)/a-TiB 2 thin films by way of activating phase segregation. Increasing nitrogen content accelerated further segregation of phase, accompanied with formation of nanocomposite nc-TiN/a-TiB 2 thin films and fast increase of microhardness value. A maximum microhardness value of about 52 GPa was obtained at TiB 0.52N 0.63. Further increase of N content accelerated formation of BN bonding, followed by formation of nc-TiN/a-TiB 2/a-BN thin films and fast decrease of microhardness value. The residual stress was not consistent with the microhardness, and showed linear increase with increasing N content. The thermal stability of Ti–B–N thin films strongly depended on microstructure and phase configuration. A high thermal stability usually occurred at an optimum composition which had a high microhardness value.

Effects of nitrogen content on microstructure and oxidation behaviors of Ti–B–N nanocomposite thin films

Several different types of thin films, TiB0.65,TiB0.62N0.18,TiB0.61N1.04, and pure TiN, were deposited on Si(100) substrates at 500 °C by reactive unbalanced close-field dc-magnetron sputtering using two Ti and two TiB2 targets. The oxidation experiments of these films were carried out in air at fixed temperatures in a temperature regime of 600–1000 °C. As-deposited and oxidized films were characterized and analyzed using x-ray diffraction, plan-view and cross-sectional scanning electron microscopies, atomic force microscopy, and x-ray photoelectron spectroscopy (XPS). It was found that the microstructure and bonding configuration of Ti–B–N thin films were strongly dependent on nitrogen flow rate during deposition. Depending upon the amount of N addition, the films showed two- or three-phase nanocomposite structure. Nitrogen-free films were amorphous compound comprising of Ti and TiB2 (Ti–TiB2 compound). At 10 at. % N addition (TiB0.62N0.18), the films consisted of mainly TiN and TiB2 bondings with microstructures comprising of nanocrystalline (nc)-Ti(N) embedded in an amorphous (a)-TiB2 matrix. As the N concentration increased up to 38 at. % (TiB0.61N1.04), the films consisted of nc-TiN in a-(TiB2, BN) matrix. The oxidation experiment illustrated that the nanocomposite TiB0.61N1.04 thin films exhibited a much higher high-temperature oxidation resistance than TiN, TiB0.65, and TiB0.62N0.18 thin films. A two-stage oxidation process took place in these nanocomposite films in the whole temperature regime. A low oxidation rate accompanied with formation of small-grained Ti oxide occurred below 800 °C, while above 800 °C a rapid oxidation process accompanied with formation of large-grained Ti oxide with rough surface took place. It is believed that the two-stage oxidation process was related to oxidation resistance of nanocrystallites and thermal stability of amorphous matrix phase. By XPS, the oxides were determined to consist mainly of various types of Ti oxides in the oxidation temperatures of 600–1000 °C, such as TiO, TiNxOy, Ti2O3, and TiO2. It was also found that no elemental B was detected in oxide formed above 600 °C, which may be due to a low melting temperature of B2O3.

Use of BN as a reactant in combustion synthesis of TiN [sbnd]TiB 2 composites under nitrogen pressure

An experimental study on direct formation of TiN TiB 2 composites by self-propagating high-temperature synthesis (SHS) was conducted using compacted samples of titanium (Ti) and boron nitride (BN) powders ignited in gaseous nitrogen. Effects of sample green density, nitrogen pressure, starting stoichiometry of reactant compacts, and diluent content on the degree of conversion and combustion characteristics were investigated. With the addition of TiN as a diluent in the sample, TiN TiB 2 composites with the TiB 2 content ranging from 12.5 to 33.3 mol.% were produced at relatively low pressures of nitrogen. Experimental results showed that the TiN–33.3 mol.% TiB 2 composite was directly synthesized from SHS reaction of the 1.5Ti + BN sample in argon. Moreover, combustion of a 60% TMD sample made up of 2Ti + BN achieved complete nitridation in nitrogen of 1.48 MPa and yielded a composite of TiN–25 mol.% TiB 2. However, due to the melting of reactant compacts in combustion the degree of nitridation was relatively low for the undiluted samples of 3Ti + BN and 4Ti + BN, implying that the addition of diluent TiN was required in order to achieve the full conversion. For the reactant compacts of 60% TMD, the TiN-diluted samples of 2.5Ti + BN + 0.5TiN and 3Ti + BN + TiN reached complete nitridation at 1.14 MPa of nitrogen and produced TiN TiB 2 composites with the TiB 2 concentrations of 16.7 and 12.5 mol.%, respectively. For the end products of incomplete conversion, XRD analysis identified not only desired phases of TiN and TiB 2, but intermediate compounds of Ti 2N and TiB.

Titanium–titanium diboride composites as part of a gradient armour material

In the world today there is an increasing use of small-calibre armour piercing projectiles and these constitute a growing threat. This threat is most eminent for wearers of body armour and to lightly armoured combat vehicles. As part of the solution to this problem, new generations of lightweight armour designs are under development. One promising possibility has been found to be the use of functionally gradient materials as armour materials. In such materials, the high hardness of ceramics is combined with the ductility of metals; in our study the system of Ti–TiB 2 was used. As compaction and consolidation process the spark plasma sintering process was used. Though similar to conventional hot pressing, no external heat source is needed; instead a pulsed direct current is passed through the electrically conducting pressure die and through the sample. At low sintering temperatures with short holding times (minutes), fully dense materials can be obtained, benefiting in little grain growth. Mechanical and impact experiments of single ceramic metallic composites layers have been carried out. The ballistic tests were done on discs glued to steel backings, and tungsten core projectiles, calibre 7.62 mm, were used. The ballistic results indicate a suitable composition, which does not have to be a pure ceramic, for the outer high hardness armour layer. To verify the suitability of the spark plasma sintered material, a comparison was made on the mechanical and ballistic properties between SPS-(Ti) 0.05(TiB 2) 0.95 and HIP-TiB 2, and it was found that the SPS-material was the overall better protective material.

Titanium-boride eutectic materials: Phase equilibria and properties of alloys in the Ti-rich portion of the Ti–Sn–B system

Phase equilibria in the Ti–TiB–Ti 3Sn region of the Ti–Sn–B system were experimentally investigated in the melting (solidification) temperature range using metallography (including EPMA), XRD, DTA, and pyrometry. The phase diagram is presented as solidus and liquidus surfaces projections and a vertical section through the 7.5 at.% B. The Sn alloying was found to have a profound hardening effect on the eutectic titanium-boride alloys.

Spark plasma sintering of functionally graded material in the Ti–TiB 2–B system

A six-layer functionally gradient material (FGM) of Ti–TiB–TiB 2 was rapidly fabricated by spark plasma sintering (SPS) in vacuum. Both B and TiB 2 were used and reacted with Ti to synthesize TiB. Adjusting the content ratio of B to TiB 2 in individual layers could control the amount of synthesized TiB by two steps during sintering. The composition and microstructure of the layers in FGM were investigated by XRD, SEM and TEM. The synthesized TiB has needle-like, agglomerated and elongated morphologies. The content of agglomerated TiB increased and that of needle shape TiB decreased with increasing the target TiB volume fraction ranging from 20 to 60%. The elongated TiB was observed in the other two layers with higher target TiB volume fraction, which structure is similar to the agglomerated TiB. The FGM with Ti on one side to Ti–TiB–TiB 2 on the other were fabricated at relative low sintering temperature and short dwelling time by spark plasma sintering.

Self-propagating high temperature combustion synthesis of TiB/Ti composites

Dense TiB/Ti composites were fabricated by Self-propagating High Temperature Synthesis connected with Pseudo Hot Isostatic Pressing (SHS/PHIP). T ads, T c and combustion velocities of the TiB– xTi system decrease with increasing the amount of Ti. The synthesized TiB–Ti cermets mainly consisted of TiB and Ti phases, but TiB 2 phase existed in some products with lower content of metal. Needle-like, rod-like or plate-like TiB grains formed in the microstructure of synthesized TiB– xTi composites. The size of the TiB grains decreased with an increasing amount of metal addition. The hardness and relative density of the synthesized materials are all beyond HRA82 and 94%, respectively. The introduction of Ti into TiB– xTi cermets resulted in a drastic increase in the bending strength, tensile strength, compression strength, fracture toughness and the maximum values were obtained with the addition of 40 wt.%Ti.

Fabrication of TiB 2 reinforced Al 3Ti composite layer on Ti substrate by reactive-pulsed electric current sintering

A TiB 2 reinforced intermetallic compound Al 3Ti composite coating layer was formed by reactive-pulsed electric current sintering of mechanically alloyed Al–Ti–B or Al–Ti–TiB 2 powders, and was simultaneously bonded to a Ti substrate to improve its wear and oxidation properties. The sintering behavior was investigated to obtain a fully dense and homogeneous Al 3Ti/TiB 2 coating. Bonding to substrate was achieved by the formation of reaction layers at the bonding interface and the reaction kinetics were investigated. Although the wear properties of monolithic Al 3Ti coating could be improved by the reinforcement of TiB 2, the oxidation properties at high temperature (1273 K) were degraded due to the decomposition of TiB 2 to elemental Ti and B.

Combustion synthesis processing of functionally graded materials in the Ti–B binary system

In this study, fabrication of functionally graded materials from elemental powders of Ti and B by utilizing combustion synthesis technique was investigated. The technique was chosen because it exploits the exothermic reaction between titanium and boron. The control of the reactions was achieved by selecting compositions away from the stoichiometry without resorting to adding a third element into the system. Compositionally graded trilayered (Ti-10–18 wt.%B, Ti-5–15 wt.%B) and five layered (Ti-5–10–15–18 wt.%B) green compacts were ignited. The influence of the composition selection and the temperature on propagation and product formation was studied. In order to achieve more control of the exothermic reactions, the titanium side was ignited first. Therefore in functionally graded material (FGM) compacts, a relatively longer ignition time and higher reaction temperatures were recorded compared to corresponding single compositions. X-ray diffraction studies showed that, due to high exothermicity, TiB and TiB 2 formed even at off-stoichiometric compositions. Such reactions produced FGMs with titanium on one side to Ti–TiB–TiB 2 on the other. The as-fabricated Ti–TiB–TiB 2 graded composite materials exhibited continuous and crack free interfaces.

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.

Processing and characterization of metal–ceramics functionally gradient materials

Functionally gradient materials (FGMs) are receiving great attention as they provide optimum thermal and mechanical properties without a discrete interface between two materials. By controlling the chemical composition and microstructure, Ti–TiB 2 based FGM was developed successfully in the present work. Microstructural studies have shown a uniform composition and microstructure gradients in the present FGM system. The effect of particle size and SiC additive on the sintering of the FGM were investigated. The bending strength and fracture toughness of the FGMs fabricated using various processing parameters were also measured.