Titanium Monoboride Research Articles

The Chemistry-Process-Structure Relationships of a Functionally Graded Ti-6Al-4V/Ti-1B Alloy Processed with Laser-Engineered Net Shaping Creates Borlite.

We quantify the chemistry-process-structure-property relationships of a Ti-6Al-4V alloy in which titanium-boron alloy (Ti-B) was added in a functionally graded assembly through a laser-engineered net shaping (LENS) process. The material gradient was made by pre-alloyed powder additions to form an in situ melt of the prescribed alloy concentration. The complex heterogeneous structures arising from the LENS thermal history are completely discussed for the first time, and we introduce a new term called "Borlite", a eutectic structure containing orthorhombic titanium monoboride (TiB) and titanium. The β-titanium grain size decreased nonlinearly until reaching the minimum when the boron weight fraction reached 0.25%. Similarly, the transformed α-titanium grain size decreased nonlinearly until reaching the minimum level, but the grain size was approximately 2 μm when the boron weight fraction reached 0.6%. Alternatively, the α-titanium grain size increased nonlinearly from 1 to 5 μm as a function of the aluminum concentration increasing from 0% to 6% aluminum by weight and vanadium increasing from 0% to 4% by weight. Finally, the cause-effect relationships related to the creation of unwanted porosity were quantified, which helps in further developing additively manufactured metal alloys.

Simultaneous enhancements of strength, ductility, and toughness in a TiB reinforced titanium matrix composite

In titanium matrix composites (TMCs), the enhancement in strength and specific stiffness with the addition of ceramic reinforcements often occurs with lowered ductility and fracture toughness. The latter is primarily due to the location of the reinforcement particles at the grain boundaries (GBs). In the current work, it is illustrated that it is possible to enhance the strength, ductility, and fracture initiation toughness (KQ) simultaneously if the particles are micron sized and predominantly present within the grains. For this purpose, TMCs (in which the majority of titanium monoboride (TiB) particles present intra-granularly) are synthesized using the powder metallurgy technique, and their microstructures and the uniaxial tensile properties, mode I fracture toughness, and fatigue crack growth behavior were evaluated. Interrupted uniaxial tensile tests reveal that the intragranular TiB particles enhance the strain hardening rate, by resisting the planar slip, which is otherwise dominant in the Ti matrix; the particles present at the GBs fracture prematurely and compromise the ductility and the toughness of the material. Such significant differences in the roles played by the inter- and intra-granular TiBs in determining the overall mechanical performance of the TMCs highlight the importance of microstructural design of them, especially on the location of reinforcements with respect to GBs.

Pressure-induced novel structure with graphene-like boron-layer in titanium monoboride

The recent discovery of the novel boron-framework in boron-rich metal borides with complex structures and intriguing features under high pressure has stimulated the search into the unique boron-network in the metal monoborides or boron-deficient metal borides at high pressure. Herein, based on the particle swarm optimization algorithm combined with first-principles calculations, we thoroughly explored the structural evolution and properties of TiB up to 200 GPa. This material undergoes a pressure-induced phase transition of Pnma → Cmcm → Pmmm. Besides of two known phases Pnma and Cmcm, an unexpected orthorhombic Pmmm structure was predicted to be energetically favored in the pressure range of 110.88–200 GPa. Intriguingly, the B covalent network eventually evolved from a one-dimensional zigzag chain in Pnma-TiB and Cmcm-TiB to a graphene-like B-sheet in Pmmm-TiB. On the basis of the microscopic hardness model, the calculated hardness (H v) values of Pnma at 1 atm, Cmcm at 100 GPa, and Pmmm at 140 GPa are 36.81 GPa, 25.17 GPa, and 15.36 GPa, respectively. Remarkably, analyses of the density of states, electron localization function and the crystal orbital Hamilton population (COHP) exhibit that the bonding nature in the three TiB structures can be considered as a combination of the B–B and Ti–B covalent interactions. Moreover, the high hardness and excellent mechanical properties of the three TiB polymorphs can be ascribed to the strong B–B and Ti–B covalent bonds.

Development of TiB and nanocrystalline Ti-reinforced novel hybrid Ti nanocomposite produced by powder metallurgy

Titanium monoboride (TiB) whisker-reinforced titanium (Ti) matrix composites were produced by powder metallurgy, through vacuum sintering. TiB is formed by thermal decomposition of TiB2 precursor. In addition, a new hybrid composite was developed by admixing nanograined and nanocrystalline (more important) Ti to enhance the transformation mechanism of TiB2 to TiB phase. The morphology and particle size of the initial powders, mixtures and the microstructure of the composites have been studied by scanning electron microscopy (SEM). The phase analysis and transformation monitoring were performed by X-ray diffraction (XRD). The sintered composites were also subjected to compressive strength and hardness measurements. According to XRD results, through the addition of nanocrystalline Ti, a probable enhancement of the TiB2 → TiB transformation occurred producing more TiB whiskers in the hybrid composites. All samples of the hybrid composites exhibited improved yield strength (1365 MPa) and hardness (358 HV) compared to the non-hybrid ones 927 MPa and 254 HV, respectively.Graphical abstract

Level Set function-based Functionally Graded Material for the reduction of maximum stresses around a pair of inclined unequal circular holes

OBJECTIVE: The aim of this work is to present the methodology for grading the Functionally Graded Material (FGM) using Level Set (LS) sign distance function around the multiple holes and parametrically analyse the maximum stresses for a pair of inclined unequal circular holes surrounded by the FGM layer in an infinite plate subjected to uniaxial tensile load using the Extended Finite Element Method (XFEM). METHODS: The LS method has the ability to represent the multiple geometrical boundaries with a single sign distance function which can be effectively used for grading the FGM around the multiple discontinuities such as holes, inclusions, cracks, etc. When dealing with FGM material grading around multiple discontinuities, it is important to have smooth grading to minimise the stress concentration. The grading of the material with multiple functions may result in sharp changes in the material properties at the interference region which may lead to high stresses. The LS function-based FGM material grading eliminates such sharp changes as it uses a single function. RESULTS: The parametric analysis shows that applying the LS function-based power law FGM layer of Titanium – Titanium Mono Boride (Ti-TiB) around the pair of inclined unequal circular holes significantly reduces the values of maximum tensile as well as compressive hoop stresses when compared with the homogeneous material case.

Influence of Ti and B powder mixing modes on mixture properties and SHS composite microstructure

The paper studies the influence of mixing modes for titanium and boron powder mixtures with the 81.5 % Ti + 18.5 % B composition in a ball mill on the process characteristics of mixtures, combustion parameters, and microstructure of SHS composites. It is shown that the dependence of the electrical resistivity on the density of charge compacts for the composition under study can be used as a criterion for mixing quality, mixture uniformity. It is noted that an increase in the grinding media mass includes the mechanism of mechanical activation (MA) of mixtures. Dependences of the burning speed and temperature on density were obtained for all the mixtures under study. Burning speeds for mixtures subjected to mechanical activation (Мch/Мball = 1 : 7; 1 : 12) and without it (Мch/Мball = 1 : 4) differ significantly. Mechanically activated mixtures feature by differences in burning speeds depending on the charge compact thickness. Thin compacts burn at a higher speed. The burning speed of mixtures without MA (in case of smaller grinding media masses) does not depend on the compact thickness. Maximum burning temperatures of all the mixtures studied have insignificant differences depending on the density, mixing time and grinding media mass. There was also no any effect of the compact thickness on the burning temperature observed. The structure of SHS composites depends on mixing modes. The finely dispersed structure of composites with titanium diboride grains (less than 1 μm) and a titanium-based binder phase can be obtained only from MA mixtures. Alloys with a structure consisting mainly of elongated titanium monoboride grains (up to 40 μm) and a binder phase of a solid solution of boron in titanium were synthesized of the mixtures for which mechanical activation processes are not essential.

Structure and Phase Composition of (TiB)–Ti Metal Matrix Composites Obtained by SHS and Vacuum Sintering

The structure and phase composition of (TiB)–Ti powder metal matrix composites synthesized by wave combustion with subsequent vacuum sintering are studied. The selected ratio of the reacting components correspond to the presence of unreacted titanium in the combustion products. The behavior of the SHS composite powders synthesized by vacuum sintering is estimated. An analysis of the volumetric and structural changes in the synthesized powder compacts demonstrates that at sintering temperatures of 1300–1350°С, no significant structure transformation occurs, and a slight decrease in the compact volume and the residual pore content is observed. A qualitative phase composition is maintained regardless of the amount of excess titanium and the selected temperature of sintering of the metal matrix composite. The vacuum sintering condition facilitates the redistribution of proportions of phases formed in a nonequilibrium state during synthesis. After sintering, the titanium diboride phase content decreases in favor of a more stable titanium monoboride.

Hard Alloy Production by SHS Compaction in Open Matrix

The possibility of performing SHS for the composition (wt %) 81.5Ti + 18.5B in air with subsequent compaction of combustion products in an open steel mold with the walls limiting their radial flow under severe heat dissipation conditions without using an intermediate loose heat insulator is investigated. The preparation modes of reaction powder mixtures to the synthesis is optimized. Process characteristics such as loose density, densification, and elastic aftereffect are performed, and the strength of compacts is evaluated. It is shown that the interrelation between the strength of charge compacts, combustion rate, and variation in the volume after combustion in air occurs. The optimal density of charge compacts is found to be 0.75, which corresponds to the maximum combustion rate without charge escapes and with a minimum change in volume. As a result of the optimization, the possibility of an efficient and safe synthesis process without using an intermediate insulator friable medium is shown. Hard-alloy plates 60 mm in diameter and 11 mm in thickness are prepared under the conditions of SHS compaction in an open steel mold. The structure of prepared hard alloy is unique with porosity smaller than 0.5% and consists of titanium diboride (~60 wt %) and binder titanium-based phase (~40 wt %). Such a structure, formed due to accelerated cooling, can be determined as nonequilibrium according to the phase diagram of the Ti–B system; titanium monoboride (TiB) should be the main phase for the composition under investigation. The microhardness of the fabricated hard alloy is HV = 18 000 MPa.

Hard alloy production by SHS compaction in an open die

The paper investigates the possibility of carrying out SHS for the Ti (81.5 wt.%) + B (18.5 wt.%) composition in the air followed by pressing combustion products in an open steel die with walls limiting their radial flow under tough heat dissipation conditions without the use of an intermediate loose medium of the heat insulator. Modes of reaction powder mixture preparation for synthesis were optimized. Such process characteristics as bulk density, compaction, elastic aftereffect were determined for initial powders and reaction mixtures, and the strength of compactions was estimated. It is shown that there is a relationship between the strength of charge compacts, combustion rate and changes in their volume after combustion in the air under intensive gas liberation during combustion. The optimal charge compact density was found equal to 0.75 corresponding to the maximum combustion rate without charge emissions with a minimum change in volume. As a result of the optimization, the possibility of effective and safe conduct synthesis process without the use of an intermediate loose medium of the heat insulator is shown. Hard-alloy plates with a diameter of 60 mm and a thickness of 11 mm were obtained in the open steel die under SHS compaction conditions. The structure of the resulting hard alloy is unique with a porosity of less than 0.5 %. It consists of titanium diboride (~60 wt.%) and titanium-based binder phase (~ 40 wt.%). Such a structure obtained as a result of accelerated cooling can be defined as nonequilibrium, since the main phase for the studied composition should be titanium monoboride (TiB) in accordance with the Ti–B state diagram. The microhardness of the fabricated hard alloy is HV = 18000 MPa.

Synthesis and Electron Beam Facing of Titanium Monoboride–Titanium Matrix Composite Powders

Titanium monoboride–titanium composite powders with the titanium matrix content from 20 to 60% are obtained by self-propagating high temperature synthesis (SHS) in titanium and boron powder mixtures. The SHS powders are used for cladding of coatings with a thickness of up to 3 mm on a VT1-0 titanium sheet by electron beam facing. The phase composition and microstructure of the initial powders and cladded coatings are investigated via X-ray diffraction analysis and optical and scanning electron microscopy. On the basis of the microstructure investigation and microhardness profiles in the coating/base plate transition zone, a conclusion about effective adhesion of the coating to the base plate is made. The dependence of the hardness and abrasive wear resistance of the cladded coatings on the phase composition of the powders used for cladding is studied. It is found that the hardness of the coatings strengthened by needle-like titanium monoboride inclusions in the titanium matrix is 2.2-fold higher and abrasive wear is 3.7-fold higher when compared to the properties of VT1-0 titanium. Here, the effect of strengthening and increase in the wear resistance of the titanium matrix by titanium monoboride particles is much smaller than similar effects in the case of the use of disperse titanium carbide particles as the strengthening phase in cladded coatings.

Free SHS-compression method for producing large-sized plates from ceramic materials

Large-sized plates (120×80×8 and 80×40×8 mm) were obtained from a material based on titanium monoboride by the method of free SHS-compression using press equipment with a force of up to 120 kN. The structural features of the obtained materials, their physicomechanical properties were investigated, the samples were annealed in an oxidizing environment for 10 hours at 1100 ° C.

The Influence of Aluminum Nitride Nanoparticles on the Structure, Phase Composition, and Properties of TiB/Ti-Based Materials Obtained by SHS Extrusion

Compact ceramic long-dimensional materials based on titanium monoboride modified with aluminum nitride dopants (3 and 5 wt %) were obtained via SHS extrusion. Titanium monoboride was produced using azide technology of self-propagating high-temperature synthesis (SHS-Az). Small dopants of nanoscaled aluminum nitride powder exert a strong influence on the phase composition, structure, and physicomechanical properties of samples prepared by SHS extrusion. Scanning electron microscopy data reveal the refinement of the main titanium monoboride phase grains in modified samples. The most pronounced refinement of titanium monoboride grains is observed as the AlN nanopowder content is increased to 5 wt %. The combustion characteristics (temperature and combustion rate) are measured in an installation simulating the real SHS extrusion conditions. It is established that AlN at its content of 3 wt % in the initial charge interacts with the titanium matrix during combustion with the formation of the Ti2AlN and Ti4AlN3 MAX phases. AlN at a concentration of 5 wt % undergoes decomposition during combustion with release of titanium nitrides and pure aluminum, as well as the TiB, TiB2 and Ti2AlN phases. Modified compact ceramic materials are shown to exhibit higher microhardness in comparison with samples without using nanomodified AlN dopants.

Synthesis and electron beam facing of TiB – TiC – titanium matrix hybrid composite powders

TiB – TiC – titanium matrix composite powders have been synthesized by self-propagating high temperature synthesis (SHS) in titanium, boron and carbon reactive powder mixtures. A target volume content of the titanium matrix (binder) in the powders was 50%. The SHS powders were cladded on VT1-0 titanium sheet by electron beam facing. A thickness of the cladded coatings varied from 1 to 3 mm depending on the pass number. A phase composition and a structure of the SHS powders and of the cladded coatings were invetigated be X-ray diffraction, optical and scanning electron microscopy. According to structure investigation and hardness profiles in the “coating – titanium base plate” transition zone an adhesion of the coating to the base is high. The hardness and abrasive wear resistance tests of the cladded coatings were carried out depending on the powder used for cladding. The maximum hardness increase of the coatings strengthened by titanium monoboride and titanium carbide inclusions is 2.2 times and abrasive wear resistance – 4.3 times as compared with VТ1-0 base. According to authors’ earlier results enhance hardness and abrasive wear resistant effects of titanium matrix by titanium carbide particles and titanium monoboride is near to the wear resistance of coatings deposited with SHS TiB + Ti powder, but ~5 times less than the wear resistance of coatings surfaced with SHS powder TiC + Ti.

Synthesis and electron beam facing oftitanium monoboride – titanium matrix composite powders

Titanium monoboride – titanium matrix composite powders have been synthesized by self-propagating high temperature synthesis (SHS) in titanium and boron reactive powder mixtures. Titanium matrix (binder) content varied from 20 to 60%. The SHS powders were cladded on VT1-0 titanium sheet by electron beam facing. Cladded coatings’ thickness varied from 1 to 3 mm depending on the pass number. Phase composition and structure of powders and coatings were investigated by X-ray diffraction, optical and scanning electron microscopy. According to structure investigation and hardness profiles view in the “coating – titanium base plate” transition zone an adhesion of the coating to the base is high. The hardness and abrasive wear resistance tests of the cladded coatings were carried out depending on the powder used for cladding. The maximum hardness of the coatings strengthened by eagle-like titanium monoboride inclusions as compared with VТ1-0 base increases 2.2 times and abrasive wear resistance 3.7 times. According to previously obtained results hardening and abrasive wear resistance of titanium monoboride is much weaker than that of titanium carbide: hardness increases 1.7 times, wear resistance 5.8 times.

Improvement of wear behaviour of titanium by boriding

PurposeThe purpose of this paper is to achieve a hard and protective borided layer on commercially pure Ti (grade-2) by applying boriding, and to investigate the changes in its microstructure, hardness, friction and wear behaviors.Design/methodology/approachPack boriding technique was used to form a hard boron diffusion layer on titanium substrate. A powder mixture of amorphous boron and anhydrous borax was used as a solid-state boriding media, and then the boriding was carried out under inert atmosphere.FindingsA thick dual boride layer consisting of a monolithic titanium diboride (TiB2) on the top and titanium monoboride (TiB) whiskers beneath that layer formed at relatively low diffusion temperature under pressured inert argon atmosphere in a boriding media containing boron source and activator. With boriding at specified conditions, very hard (4100 Hv0.01) and thick monolithic TiB2 layer formed on the top-most layer which is required for improved tribological applications. Hardness decreased gradually through the TiB whisker layer and finally reached to the hardness of base material.Originality/valueThis paper investigates the effects of components of boriding mixture and conditions of thermal treatment on the formation of borided layer and its properties. In previous studies, boriding mixtures containing a boron source, an activator and a filler material was generally used at high temperatures around or above 1,050°C to achieve a thick monolithic layer on the top of the surface of titanium. In the present study, no filler material was used to accelerate the boron diffusion because filler materials may inhibit the diffusion of boron atom through the surface of substrate of titanium. Also, diffusion treatment was carried out under pressurized argon atmosphere at relatively low diffusion temperature to achieve boride layer with the improved hardness and durability.

Ceramic Ti—B Composites Synthesized by Combustion Followed by High-Temperature Deformation

Long compact cylindrical rods, which consist of a titanium monoboride-based TiB—30 wt % Ti ceramic composite material, are synthesized during combustion of the initial components (titanium, boron) followed by high-temperature deformation. High-temperature deformation is found to affect the orientation of the hardening titanium monoboride phase in the sample volume and the phase composition of the sample. The combustion temperature is studied as a function of the relative density of the initial workpiece under the experimental conditions.

Recrystallization behavior of boron-modified commercial-purity titanium during hot deformation

A comparative investigation of the recrystallization behavior of as-cast commercial-purity (CP) titanium VT1-0 with addition of 0.2 wt % boron and of unalloyed CP titanium in the hot-rolled and as-cast states has been performed. The introduction of boron leads to the formation of uniformly distributed short filaments and particles of titanium monoboride (TiB), which stimulates a substantial refinement of the cast structure. The recrystallization behavior of the alloys was studied after deformation by compression at T = 900-600°C using the EBSD analysis. It has been established that the kinetics of the recrystallization of the as-cast VT1-0-0.2B alloy is substantially accelerated compared with that of the unalloyed VT1-0 alloy due to the presence of borides. The recrystallization behavior of the VT1-0 alloy with the initial hot-rolled structure and of the VT1-0-0.2B alloy with the as-cast structure proved to be approximately similar. Based on the investigations performed, recommendations have been made that should facilitate (and reduce the cost of) the production of fine-grained and ultrafine-grained semi-finished items of CP titanium.

Selective laser melting of in situ titanium–titanium boride composites: Processing, microstructure and mechanical properties

This study presents results of selective laser melting (SLM) processing of in situ Ti–TiB composites from optimally milled Ti–TiB2 powder. Optimized tuning of the SLM manufacturing parameters was applied to obtain almost fully dense (>99.5%) Ti–TiB composites. X-ray diffraction and electron diffraction patterns as well as microstructural investigations indicate a chemical reaction during SLM in which irregular-shape titanium diboride (TiB2) particles react with pure Ti to form needle-shape titanium monoboride (TiB) particles. Transmission electron microscopy investigations reveal that Ti grains are refined significantly due to the existence of B. The microhardness, yield stress and compressive strength of the SLM-produced Ti–TiB composites increase to 402 Hv, 1103MPa and 1421MPa, respectively, compared to 261 Hv, 560MPa and 1136MPa, respectively, for the SLM-produced commercially pure Ti. These improvements are mainly due to strengthening and hardening effects induced by TiB particles and refinement of Ti grains. Fractography analyses show that a mixture of splitting/shearing and smooth/rough zones covers the fracture surfaces of failed composite samples after compression testing.

Fractal Geometric Characterization of Functionally Graded Materials

The complex structure and mechanics of elastoplastic functionally graded materials (FGM) is studied from the standpoint of fractal geometry. First, upon introducing the fineness as the number of grains of either phase across the FGM, the two-phase FGM is characterized using fractals, and an interfacial fractal dimension is estimated for varying degrees of fineness. A variation in local fractal dimension is considered across or along the FGM domain, and it is characterized by Fourier series and Beta function fits. Assuming the FGM is made of locally isotropic Titanium (Ti) and Titanium Monoboride (TiB), pure shear tests are simulated using ABAQUS for fineness levels of 50, 100, and 200 under the uniform kinematic boundary condition (UKBC) and the uniform static boundary condition (USBC). The material response observed under these BCs shows high sensitivity of these systems to loading conditions. Furthermore, plastic evolution of Ti grains, assuming isotropic plastic hardening, displays a fractal, partially plane-filling behavior. Fractal dimensions of sets of plastic grains are calculated using the box-counting method, validating the mechanical results, thus again showing high sensitivity of this material system to loading conditions.

Microstructure and mechanical characteristics of VT1-0-Based composite material reinforced by titanium monoboride

The microstructure and mechanical characteristics of commercially pure titanium, i.e., the VT1-0 alloy, modified by 1.5 wt % B have been studied. It has been found that, during the melting of an ingot, uniformly distributed titanium monoboride (TiB) fibers up to O5 × 150 μm in size appear in the material in a volume fraction of about 8%. The results of compressive and tensile tests show that this composite material substantially surpasses pure titanium in the strength characteristics, with retaining satisfactory plasticity.