TiB Needles Research Articles

Microstructural examination and ballistic testing of field-assisted sintering technology produced Ti-TiB2 functionally graded material composite armour plates

High hardness ceramics are potent in their use for armour applications globally, but intrinsically brittle. This can result in fragmentation damage, as well as low multi hit capacity. In this work, alternative 250 mm diameter Ti-6Al-4 V discs were produced using field-assisted sintering technology (FAST) with and without stepped functional grading using low wt.% TiB2 concentrations, respectively, to investigate their microstructure and ballistic performance. The in situ generation of a significant quantity of high strength, ceramic TiB needles was confirmed for the samples, and the plates were ballistically tested to attain V50 values. In addition to a microstructural examination. The ballistic results indicated a superior behavior to the monolithic titanium alloy plates without TiB2 additions.

Effect of Heat Treatment on Microstructure and Mechanical Behavior of Ultrafine-Grained Ti-2Fe-0.1B.

In the present study, a novel Ti-2Fe-0.1B alloy was processed using equal channel angular pressing (ECAP) via route Bc for four passes. The isochronal annealing of the ultrafine-grained (UFG) Ti-2Fe-0.1B alloy was conducted at various temperatures between 150 and 750 °C with holding times of 60 min. The isothermal annealing was performed at 350-750 °C with different holding times (15 min-150 min). The results indicated that no obvious changes in the microhardness of the UFG Ti-2Fe-0.1B alloy are observed when the annealing temperature (AT) is up to 450 °C. Compared to the UFG state, it was found that excellent strength (~768 MPa) and ductility (~16%) matching can be achieved for the UFG Ti-2Fe-0.1B alloy when annealed at 450 °C. The microstructure of the UFG Ti-2Fe-0.1B alloy before and after the various annealing treatments was characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the average grain size remained at an ultrafine level (0.91-1.03 μm) when the annealing temperature was below 450 °C. The good thermal stability of the UFG Ti-2Fe-0.1B alloy could be ascribed to the pinning of the TiB needles and the segregation of the Fe solute atoms at the grain boundaries, which is of benefit for decreasing grain boundary energy and inhibiting the mobility of grain boundaries. For the UFG Ti-2Fe-0.1B alloy, a recrystallization activation energy with an average value of ~259.44 KJ/mol was analyzed using a differential scanning calorimeter (DSC). This is much higher than the lattice self-diffusion activation energy of pure titanium.

Unique opportunities for microstructure engineering via trace B4C addition to Ti-6Al-4V through laser powder bed fusion process: As-built and heat-treated scenarios

This research study examines the role of minor B 4 C addition (0.2 wt%) in improving the mechanical properties of the laser powder bed fusion (L-PBF) fabricated Ti-6Al-4V (Ti64) alloy in the as-built and heat-treated conditions. The fabricated titanium matrix composites (TMCs) were subjected to two different heat treatment scenarios, i.e., subtransus and supertransus, and were compared to the Ti64 counterparts exposed to the same thermal cycles. Both as-built and heat-treated Ti64 and TMC samples were characterized in terms of the grain structure, microstructure within the grains, and the size, morphology, volume fraction, and crystallographic orientation of the phases. The knowledge gained from microstructural investigations was correlated to the mechanical behavior of components, including compressive strength and ductility, microhardness, and scratch resistance. The governing strengthening mechanisms were identified, and the contribution of each mechanism in the overall yield strength was explored. Results revealed that TMCs possessed higher yield and ultimate compressive strengths than their Ti64 counterparts owing to the hard TiB needles homogeneously dispersed in the microstructure. However, except for the supertransus heat-treated condition, the TMCs showed slightly lower fracture strain than the Ti64 samples. The elimination of GB-α in the supertransus heat-treated TMC sample caused by the TiB needles led to a higher fracture strain than the corresponding Ti64 case. While the implemented heat treatment strategies could tailor the mechanical properties, the optimum thermal cycles for Ti64 were not necessarily applicable to TMC components.

Microstructural characterization and mechanical properties of nano-scale/sub-micron TiB-reinforced titanium matrix composites fabricated by laser powder bed fusion

A B4C/Ti-6Al-4V(Ti64) composite powder containing a minor B4C content (0.2 wt%) was developed by a novel technique and was subjected to the laser powder bed fusion (L-PBF) process within a wide range of laser powers and scanning speeds to fabricate titanium matrix composite (TMC) parts. The relative density measurement results revealed the achievement of almost fully dense TMC parts. Compared to the Ti64 case, slightly higher Ev values were required in the TMC system to obtain the highest relative density. Microstructural characterization of the TMC parts revealed the formation of large columnar prior β grains containing in-situ formed nano-scale/sub-micron TiB needles homogeneously dispersed in a martensitic matrix. While having almost the same ductility, the fabricated TMC parts showed 25% and 8% higher nanohardness, compressive yield strength, respectively, and 12% lower wear rate than the Ti64 sample. The improved mechanical properties of the TMC were due to the contribution of several factors, including the incorporation of nano-scale/sub-micron TiB reinforcement, the refinement of the martensite α՛ laths, and the solid solution strengthening effects of carbon atoms. The contribution of TiB presence and solid solution strengthening was ~60% and ~40% in the overall yield strength enhancement of the TMC parts, respectively.

Development of metal matrix composites by direct energy deposition of ‘satellited’ powders

Limited research has been undertaken investigating the material design freedoms that are granted through the use of additive manufacturing methods, especially in the development of materials specifically formulated for additive processes. In this study, a new material combination was evaluated for use with directed energy deposition methods of additive manufacturing. Here, a Ti-6Al-4 V powder is processed in combination with a much finer titanium diboride powder following a satelliting procedure. The resulting combination consists of large Ti-6Al-4 V particles encased in finer titanium diboride. Deposited composites presented exhibit TiB needles associated with increased hardness. Processing conditions were detailed which permit the deposition of the prepared feedstock onto Ti-6Al-4 V substrates. Microstructural characterisation revealed that the composite was made up of eutectic TiB precipitates dispersed in α-β Ti matrix with few partially melted Ti-6Al-4 V and TiB2 particles. Satelliting TiB2 powder onto Ti-6Al-4 V particle surfaces has significantly improved the homogeneity of composite which is characterised with randomly oriented and uniform distribution of TiB needles in the microstructure. Hardness of composites ranged between 440–480 HV. Hence, the feedstock preparation method proposed has been found to be effective and can be adapted for low cost and rapid formulation of a host of materials for processing by additive manufacture.

In-situ TiB/Ti-6Al-4V composites with a tailored architecture produced by hot isostatic pressing: Microstructure evolution, enhanced tensile properties and strengthening mechanisms

In-situ synthesized titanium borides reinforced Ti-6Al-4V composites with a tailored reinforcement architecture were successfully prepared by hot isostatic pressing (HIP) starting from a TiB2/Ti-6Al-4V powder system. The microstructure of the composite samples was investigated using X-ray diffraction (XRD) technique and scanning electron microscopy (SEM), and the mechanical properties were evaluated through room and high temperature tensile testing. It is found that during HIP the additive particles TiB2 have totally transformed into TiB needles, which tend to decorate at prior particle boundaries of the consolidated powder particles to form a network structure. With increasing TiB2 addition from 3 wt.% to 8 wt.%, the microstructural feature of the TiB network structure experiences the variations of discontinuous TiB reinforcement → quasi-continuous TiB reinforcement → continuous TiB reinforcement. The room temperature tensile properties of the composites are improved with increasing addition of TiB2 from 3 wt.% to 5 wt.%, but the tensile strength of the sample with 8 wt.% TiB2 drastically decreases. As to the high temperature properties, the titanium boride reinforced Ti-6Al-4V alloy composites can be an increased maximum service temperature by over 200 °C while retaining the same tensile strength accompanied with a suitable elongation. The strengthening mechanism is mainly attributed to the load-bearing transformation, grain refinement and dispersion strengthening.

Effect of Processing Route on Microstructure and Mechanical Properties of a Ti-3Al-2.5V/TiB Composite

A Ti-3Al-2.5V matrix composite reinforced with 8.5 vol.% TiB was produced using a powder metallurgy route. Processing included the mechanical alloying of Ti-3Al-2.5V and TiB2 powders and Hot Isostatic Pressing (HIP) of the resultant composite powders, to produce a dense billet. These billets were subsequently extruded and/or subjected to various Conversion Heat Treatments (CHT), to complete the transformation of the TiB2 particles into TiB needles. The CHT was performed either before or after extrusion. Microstructures and tensile properties of the materials at each stage of the processing routes were investigated and compared to those of a non-reinforced Ti-3Al-2.5V material, manufactured by the same powder metallurgy route. It has been demonstrated that the processing routes have a great impact on the mechanical properties, through modifications of the matrix and reinforcement characteristics. Well-chosen processing routes lead to more ductile composites, though this gain in ductility leads to slightly lower stiffness and strength values. This study clearly demonstrates the possibility to produce, at an industrial scale, a ductile version of a highly reinforced titanium matrix composite, showing important application potential.

Effect of trace lanthanum hexaboride and boron additions on microstructure, tensile properties and anisotropy of Ti-6Al-4V produced by additive manufacturing

In this work trace lanthanum hexaboride (LaB6) and elemental boron are alloyed with Ti-6Al-4V and their effects on the microstructure, tensile properties (including anisotropy) and melt pool shape during Additive Manufacturing (AM) are investigated. During the melting process, the LaB6 scavenges oxygen and decomposes into La2O3 and TiB. The presence of the rare earth element drastically changes the apparent surface tension and shape of the deposited layers. This is attributed to the Heiple-Roper effect and could have benefits during AM in producing components with unsupported overhangs. The formation of eutectic TiB during the final stages of solidification results in highly directional TiB needles in between columnar grains that are aligned with the build direction. The slow cooling rate during deposition of approximately 90–100 °C s−1 produces very large TiB particles which can exceed 50 µm in length. Although improving strength by up to 10%, under tensile stress the high aspect ratio TiB particles are sites for crack opening which leads to a decline in ductility in the longitudinal test direction and a corresponding increase in anisotropy over unmodified Ti-6Al-4V.

Phase Separation in Ti-6Al-4V Alloys with Boron Additions for Biomedical Applications: Scanning Kelvin Probe Force Microscopy Investigation of Microgalvanic Couples and Corrosion Initiation

To investigate the effect of boron additions on the corrosion behavior of Ti-6Al-4V for potential use in biomedical implants and devices, cast samples of Ti-6Al-4V were alloyed with 0.01% to 1.09% boron by weight and subjected to hot isostatic pressing. Subsequent analysis via scanning Kelvin probe force microscopy and scanning electron microscopy/energy-dispersive spectroscopy revealed the presence of both alpha (α) and beta (β) phase titanium, enriched in aluminum and vanadium, respectively. At all concentrations, boron additions affected the grain structure and were dispersed throughout both phases, but above the solubility limit, needle-like TiB structures also formed. The TiB needles and β phase exhibited similar surface potentials, whereas that of the α phase was found to be significantly lower. Nevertheless, when subjected to high applied electrochemical potentials in saline solutions, corrosion initiation was observed exclusively within the more noble β phase.

Hot isostatic pressing of in-situ TiB/Ti-6Al-4V composites with novel reinforcement architecture, enhanced hardness and elevated tribological properties

In this study, titanium borides reinforced Ti-6Al-4V composites have been successfully prepared by hot isostatic pressing (HIPing). The microstructure of the as-fabricated samples was investigated using X-ray diffraction technique, secondary electron microscopy and electron backscatter diffraction and the mechanical properties evaluated through micro-hardness and wear resistance measurements together with nano-indentation. It was found that during HIPing the additive particles TiB2 have transformed into TiB needles which tend to decorate at prior particle boundaries of the consolidated powder particles to form a network structure. Under the same HIPing condition, the needles became increasingly coarser and agglomerated with increased addition of TiB2. The micro-hardness of the synthesized materials increased with increased volume fraction of TiB. Nano-indentation measurement demonstrates that the TiB network structure shows much higher nanohardness than the surrounding matrix regions. The friction coefficient of the synthesized composites decreased continuously with increased volume fraction of TiB, indicating improved wear resistance. High resolution transmission electron microscopy analysis on wear debris revealed the formation of a series of oxides suggesting that chemical reaction between alloy elements and oxygen in air may have happened. It is thus believed that the wearing of the current samples is a result of both friction and chemical reaction.

Effect of Boron Carbide Particle Size and Volume Fraction of TiB-TiC Reinforcement on Fractography of PM Processed Titanium Matrix Composites

Effect of boron carbide particle size and volume fraction of reinforcement on fractography of PM processed Titanium matrix composites was investigated. Pressureless sintering process was established to synthesize Titanium matrix composites. Ti-B4C powder mix was consolidated and pressureless sintered to produce in-situ TiB-TiC reinforcements in titanium matrix. Scanning Electron Microscopic studies revealed presence of TiB needles and TiC particles. The composite exhibited improved flexural strength over the unreinforced titanium processed under similar conditions due to the presence of needle shaped reinforcements.

Influence of trace boron addition on the directional solidification characteristics of Ti–6Al–4V

Trace boron addition to several titanium alloys results in a reduction in the as-cast grain size by an order of magnitude. TiB needles are observed along the prior beta grain boundaries and not the grain interior in these alloys, indicating that TiB needles are not sites for the heterogeneous nucleation of beta grains. This study seeks to understand the influence of the growth rate R on microstructure evolution and grain refinement in Ti–6Al–4V–0.1B alloy using directional solidification experiments and microstructural characterization.

High-Temperature (1023 K to 1273 K [750 °C to 1000 °C]) Plastic Deformation Behavior of B-Modified Ti-6Al-4V Alloys: Temperature and Strain Rate Effects

A minor addition of B to the Ti-6Al-4V alloy, by ~0.1 wt pct, reduces its as-cast prior β grain size by an order of magnitude, whereas higher B content leads to the presence of in situ formed TiB needles in significant amounts. An experimental investigation into the role played by these microstructural modifications on the high-temperature deformation behavior of Ti-6Al-4V-xB alloys, with x varying between 0 wt pct and 0.55 wt pct, was conducted. Uniaxial compression tests were performed in the temperature range of 1023 K to 1273 K (750 °C to 1000 °C) and in the strain rate range of 10–3 to 10+1 s–1. True stress–true strain responses of all alloys exhibit flow softening at lower strain rates and oscillations at higher strain rates. The flow softening is aided by the occurrence of dynamic recrystallization through lath globularization in high temperature (1173 K to 1273 K [900 °C to 1000 °C]) and a lower strain rate (10–2 to 10–3 s–1) regime. The grain size refinement with the B addition to Ti64, despite being marked, had no significant effect on this. Oscillations in the flow curve at a higher strain rate (100 to 10+1 s–1), however, are associated with microstructural instabilities such as bending of laths, breaking of lath boundaries, generation of cavities, and breakage of TiB needles. The presence of TiB needles affected the instability regime. Microstructural evidence suggests that the matrix cavitation is aided by the easy fracture of TiB needles.

High temperature deformation processing maps for boron modified Ti–6Al–4V alloys

The alloy, Ti–6Al–4V is an α + β Ti alloy that has large prior β grain size (∼2 mm) in the as cast state. Minor addition of B (about 0.1 wt.%) to it refines the grain size significantly as well as produces in-situ TiB needles. The role played by these microstructural modifications on high temperature deformation processing maps of B-modified Ti64 alloys is examined in this paper. Power dissipation efficiency and instability maps have been generated within the temperature range of 750–1000 °C and strain rate range of 10 −3–10 +1 s −1. Various deformation mechanisms, which operate in different temperature–strain rate regimes, were identified with the aid of the maps and complementary microstructural analysis of the deformed specimens. Results indicate four distinct deformation domains within the range of experimental conditions examined, with the combination of 900–1000 °C and 10 −3–10 −2 s −1 being the optimum for hot working. In that zone, dynamic globularization of α laths is the principle deformation mechanism. The marked reduction in the prior β grain size, achieved with the addition of B, does not appear to alter this domain markedly. The other domains, with negative values of instability parameter, show undesirable microstructural features such as extensive kinking/bending of α laths and breaking of β laths for Ti64–0.0B as well as generation of voids and cracks in the matrix and TiB needles in the B-modified alloys.

Titanium composite materials for transportation applications

Discontinuously reinforced titanium alloys containing in-situ formed TiB needles are emerging as candidate materials for advanced applications. This new family of titanium composites presents technical advantages, and it can be less expensive and easily amenable for net-shape manufacturing relative to titanium metal-matrix composites developed to date. The production of a master compound by a novel and cost-effective process called self-propagating high-temperature synthesis (SHS) has been studied. This master compound could be subsequently used in an investment casting process to obtain TiB-reinforced net-shape titanium-matrix composites. The SHS technique and its features were investigated in depth before a suitable master compound was defined and produced. Cast samples obtained from the addition of the master compound have been produced and the most important issues concerning the processing, microstructure, and mechanical properties are highlighted in this paper.

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.

Spark plasma sintering reaction synthesized TiB reinforced titanium matrix composites

Abstract The in situ TiB particle reinforced titanium metal matrix composites were prepared using MA followed by park plasma sintering (SPS) with a heating rate of 50 °C/min. The in situ TiB were synthesized by chemical reaction between TiB2 and Ti during the SPS process. The microstructure of the composites sintered at 800, 1000 and 1200 °C were investigated. TiB whiskers are needle-shape and uniformly dispersed in the titanium matrix. The interface between the in situ TiB needles and the titanium matrix is singular and faceted. The composite sintered at 1000 °C has a maximum value of relative density of 99.6%, and good mechanical properties with a flexural strength of 1007 MPa, Young's modulus of 146 GPa and fracture toughness of 8.64 MPa·m1/2, respectively. The fractographs of all composites exhibit a predominantly brittle cleavage fracture mechanism. The elastic modulus of synthesized TiB was estimated.

Rapid synthesis of Ti alloy with B addition by spark plasma sintering

Abstract The in situ TiB/Ti–4.0Fe–7.3Mo composites were fabricated by plasma spark sintering (SPS) technique using mechanical alloying of Ti, Fe65Mo and B powder. The effects of sintering temperature on densification of the composites and microstructure of the in situ synthesized TiB were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). A dense composite was obtained after sintering at 1000 °C for 5 min. Under proper ball milling and SPS conditions in situ TiB reinforced Ti–4.0Fe–7.3Mo composites have been prepared. The in situ TiB showed a typical needle shape grow along [0 1 0] direction. The transverse cross-section of TiB grain is a hexagonal shape with the planes of (1 0 0), (1 0 1) and ( 1 0 1 ¯ ) . The stacking faults in the (1 0 0) plane were observed in the TiB needles.

Microstructure and Properties of TiB/Ti-6Al-4V Coatings Produced With Laser Treatments

TiB/Ti-6Al-4V metal-matrix composite (MMC) layers were produced on Ti-6Al-4V substrates by laser cladding. A TiB2/Ti powder mixture was used as a precursor to obtain a dispersion of TiB needles in the Ti alloy matrix, with the aid of an exothermic reaction between TiB2 and Ti. A eutectic microstructure was obtained that consisted of an extremely homogeneous dispersion of TiB eutectic needles in the Ti alloy matrix, having a volume fraction as high as 0.33. Also, an equilibrium-like microstructure was found, consisting of a dispersion of both primary and eutectic TiB needles inside the Ti alloy matrix. An analysis of the geometry of the layers was performed and proved successful in determining the percentage of B. Further, it correctly predicted the variation of atomic B content as a function of laser power. The relative wear resistance coefficient, defined as the wear coefficient of the uncoated matrix divided by that of coating, shows an improvement by a factor as high as 1500 for the eutectic microstructure.

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.