TiB Whiskers Research Articles

Multiphase polymorphic nanoparticles reinforced titanium matrix composite produced by selective electron beam melting of a prealloyed composite powder

A Ti−6Al−3Sn−4Zr−0.9Mo−0.4Si−0.4Y−0.5B (wt.%) titanium alloy matrix composite (TMC) with multiphase polymorphic TiB whiskers and Y2O3 and (Ti, Zr)5Si3 nanoparticles was successfully fabricated by selective electron beam melting (EBM) of a prealloyed composite powder. The rapid hypoeutectic solidification during EBM results in a columnar dendritic microstructure with three dimensional fine networks of TiB whiskers and Y2O3 nanoparticles uniformly distributed in the interdendritic regions of the parent β-Ti phase. This EBM-built TMC exhibits a remarkably enhanced tensile strength and hardness compared with its matrix alloy at room temperature and elevated temperatures up to 700°C. The ultimate tensile strength of the EBM-built TMC reaches 1185 MPa with an elongation to fracture of 3.2% at room temperature, and still retains a high value of 750 MPa at 600°C. This study opens up a new way to manufacture high-performance components of TMCs with multiphase polymorphic reinforcements and complex shapes.

Precipitation and Distribution Behavior of In Situ-Formed TiB Whiskers in Ti64 Composites Fabricated by Selective Laser Melting

The precipitation and distribution behaviors of in situ-formed titanium boride whiskers (TiB) in TiBw-reinforced Ti-6%Al-4%V (Ti64) composites fabricated from an elemental mixture of Ti64 alloy powder and TiB2 particles by selective laser melting were investigated. The primary precipitation of TiB whiskers strongly depends on B content. For a B content of less than 2 mass%, when the liquid → β-phase transformation occurred and B atoms were discharged, the B-enriched area formed around the β-phase resulted in the generation of TiB whiskers and their agglomeration at the prior β-grain boundaries. When the B content was over 2 mass%, TiB whiskers directly precipitated from the liquid phase and moved to the molten pool boundary via Marangoni convection. As a result, the TiB whiskers were located along the boundary. Furthermore, B-enrichment caused a decrease in the liquidus temperature and thus obstructed β-grain coarsening, and as a result, fine equiaxed α’-grains formed during the phase transformation.

Simultaneously enhancing strength and ductility in graphene nanoplatelets reinforced titanium (GNPs/Ti) composites through a novel three-dimensional interface design

The interface debonding caused by mismatched thermal expansion is a key issue in graphene nanoplatelets/Ti matrix composites (GNPs/TiMCs), which significantly decreases the composites' mechanical properties. In this study, GNPs/Ti composites were fabricated by spark plasma sintering (SPS) followed by heat treatment (HT) routes. A novel strategy that strengthening the GNPs-Ti interface bonding via tailored three-dimensional (3D) interface configuration was proposed for the first time. Characters of interface evolution (before and after HT processes) were discussed detailedly in conjunction with the in-situ formed TiB whiskers (TiBw). The interfacial microstructure displayed that GNPs was used as template for the heteroepitaxial growth of TiBw, then TiBw connected the TiC layer and the adjacent Ti matrix. Tensile tests showed that GNPs-(TiBw)/Ti composites exhibited excellent strength-plasticity compatibility as compared to GNPs/Ti. Ex-situ compression tests of micro-pillars fabricated from the bulk composites revealed that the 3D interface configuration in GNPs-(TiBw)/Ti possessed significantly higher strain accommodation and strain-hardening ability during deformation. This study highlights the importance of interface optimization, which is helpful for developing the interfacial engineering and achieving good properties in GNPs/TiMCs.

Laser Beam Welding of a Ti-15Mo/TiB Metal–Matrix Composite

A Ti-15Mo/TiB metal–matrix composite was produced by spark plasma sintering at 1400 °C. The fractions of the elements in the initial powder mixture were 80.75 wt.% Ti, 14.25 wt.% Mo, and 5 wt.% TiB2. The initial structure of the synthesized composite was composed of bcc β titanium matrix and needle-like TiB reinforcements with an average thickness of 500 ± 300 nm. Microstructure and mechanical properties of the composite were studied after laser beam welding (LBW) was carried out at room temperature or various pre-heating temperatures: 200, 400, or 600 °C. The quality of laser beam welded joints was not found to be dependent noticeably on the pre-heating temperature; all welds consisted of pores the size of which reached 200–300 µm. In contrast to acicular individual particles in the base material, TiB whiskers in the weld zone were found to have a form of bunches. The maximum microhardness in the weld zone (~700 HV) was obtained after welding at room temperature or at 200 °C; this value was ~200 HV higher than that in the base material.

Influence of 2D forging processes and boron contents on the microstructures and mechanical properties of near α titanium alloys

2D forging processes are adopted to tailor the microstructures and mechanical properties of near α titanium alloys with different boron contents and the evolutions of the microstructures and mechanical properties of the acquired alloys are carefully characterised. Maximum texture intensities decrease with increasing boron contents, thereby illustrating the improvements in the homogeneity of the microstructures. The distribution of TiB whiskers in the 3D space exhibits a near-columnar arrangement around boundaries of squashed and elongated prior β grains along the stretching direction. Increases in the contents of equiaxed α grains with increasing TiB contents are ascribed to enhancements in recrystallisation due to the promotion effects of the TiB phase and increases in β transus temperatures. Boron exhibits excellent refinement effects on the alloy matrices, and the refinement degree increases with increasing boron contents. The proportions of low-angle grain boundaries decrease whilst the corresponding proportions of high-angle grain boundaries increase with increasing boron contents. The ultimate and yield strengths of the alloys increase at room temperature (RT) and 650 °C. Elongations exhibit a decreasing trend at RT but are maintained at 650 °C. At RT, cleavage fractures of the TiB whiskers determine the evolution law of elongation. The fracture characteristics of alloy matrices exhibit a transformation from a mixture of tearing lamellae and dimples to dimples only. At 650 °C, the alloy matrices are characterised by ductile fractures with numerous dimples. Er containing particles facilitate the fracture of alloy through cooperative effects with TiB whiskers.

Microstructures and mechanical properties of hot indirect extruded in situ (TiB + TiC)/Ti6Al4V composites: Effect of extrusion temperature

In this work, (TiB + TiC)/Ti6Al4V composites (TMCs) were prepared by in situ synthesis technology, and were successfully hot indirect extruded at four extrusion temperatures containing below and above β phase transition temperature (T = 1214K, 1259K, 1304K and 1349K). The effect of extrusion temperatures on the matrix, reinforcements and strengthening mechanisms were systematically studied. The results show that the mechanical effects has significantly influence on the microstructures of TMCs below β transformation temperatures, and more elongated α grains are formed. At the temperature of 1214K the α grain refinement mechanisms are controlled by dislocation motion, and there are a large number of dislocations within or between grains, which make the main contribution to the highest yield strength of the TMCs. With the increase of extrusion temperature, the yield strength decreases gradually, while the elongation increases gradually at first and then decreases slightly. This is because the grain refinement mechanism is mainly dynamic recrystallization, and coarser and dislocation-free α grains are formed at the temperature of 1349K. The indirect extrusion temperature should be controlled below the β transus. However, lower or near β transus can result in more fractures of TiB whiskers, which has a negative effect on the mechanical properties of TMCs.

Analysis of the Microstructure and Mechanical Properties of TiBw/Ti-6Al-4V Ti Matrix Composite Joint Fabricated Using TiCuNiZr Amorphous Brazing Filler Metal.

TiB crystal whiskers (TiBw) can be synthesized in situ in Ti alloy matrix through powder metallurgy for the preparation of a new type of ceramic fiber-reinforced Ti matrix composite (TMC) TiBw/Ti-6Al-4V. In the TiBw/Ti-6Al-4V TMC, the reinforced phase/matrix interface is clean and has superior comprehensive mechanical properties, but its machinability is degraded. Hence, the bonding of reliable materials is important. To further optimize the TiBw/Ti-6Al-4V brazing technology and determine the relationship between the microstructure and tensile property of the brazed joint, results demonstrate that the elements of brazing filler metal are under sufficient and uniform diffusion, the microstructure is the typical Widmanstätten structure, and fine granular compounds in β phase are observed. The average tensile strength of the brazing specimen is 998 MPa under room temperature, which is 97.3% of that of the base metal. During the high-temperature (400 °C) tensile process, a fracture occurred at the base metal of the highest tensile test specimen with strength reaching 689 MPa, and the tensile fracture involved a combination of intergranular and transgranular modes at both room temperature and 400 °C. The fracture surface has dimples, secondary cracks are generated by the fracture of TiB whiskers, and large holes form when whole TiB whiskers are removed. The proposed algorithm provides evidence for promoting the application of TiBw/Ti-6Al-4V TMCs in practical production.

The impact of matrix texture and whisker orientation on property anisotropy in titanium matrix composites: Experimental and computational evaluation

In order to understand the relationship between microstructure and mechanical property as well as provide new guidance for composites design, the impacts of matrix texture and TiB whisker orientation on anisotropy of mechanical properties in hot-rolled titanium matrix composites (TMCs) were investigated by experimental and computational methods. The results show that the matrix contains a strong transverse type (T-type) texture due to the superposition of deformation texture and transformation texture. TiB whiskers aligned along the rolling direction (RD) enhance the intensity of the 112‾0 fiber texture in the matrix due to their special orientation relationship with matrix alloy ([112‾0]α−Ti∥[020]TiB). Significant variations in elastic modulus, yield strength and ductility are all noted, depending on the orientation of the tensile axis with respect to the basal of matrix texture and whisker axis. These property anisotropies were further quantified and corroborated numerical models as a function of matrix texture and whisker orientation. Specifically, T-type matrix texture results in a lower modulus and yield strength but a higher ductility in RD. However, the aligned whiskers lead to higher modulus, yield strength and ductility in RD. The strengthening contribution from aligned TiB whiskers decreases rapidly with cos4α with increasing off-axis angle (α). Moreover, the modeling results predict that the TiB whiskers would undergo fracture if the aspect ratio exceeds ARc/cos2α; otherwise, the interfacial debonding would occur.

Precipitation behavior of silicide and synergetic strengthening mechanisms in TiB-reinforced high-temperature titanium matrix composites during multi-directional forging

To investigate the precipitation behavior of silicide and evaluate the contribution of the reinforcement phase to the properties of titanium matrix composites, a TiB-reinforced high-temperature titanium matrix composite was prepared by vacuum induction melting and multi-directional forging. The microstructure of the resultant composite after multi-directional forging was composed of a spheroidized α-phase, uniformly-distributed TiB and dual-scale silicides. The precipitation of silicides was attributed to the acceleration of elemental diffusion due to dislocations during forging. The strength of the composite after multi-directional forging at room temperature increased by about 151.9 MPa due to the fine-grain strengthening of the α-phase and the precipitation strengthening of the silicides, whereas the load-bearing efficiency of the TiB whiskers was reduced with the decrease in the aspect ratio. The strength of the multi-directional-forged titanium matrix composite at 700 °C was reduced by about 28.3 MPa. However, its plasticity was significantly improved, and the elongation reached 116.8%. The main reasons for the decrease in the strength were the easy initiation of cracks the grain boundaries and the weakening of the precipitation strengthening of the silicides.

Balance of strength and plasticity of additive manufactured Ti-6Al-4V alloy by forming TiB whiskers with cyclic gradient distribution

Elemental alloying has been demonstrated to be an effective method to improve the strength of additively manufactured Ti-6Al-4V alloys by inhibiting the formation of coarse columnar primary β grains. However, it is still a challenge to obtain a high-strength titanium alloy with high plasticity. To balance the strength and plasticity, TiB whiskers with cyclic gradient distribution were synthesized in situ as the reinforcement phase in Ti-6Al-4V alloy fabricated by wire arc additive manufacturing (WAAM) based on cold metal transfer (CMT) technology. The ultimate tensile strength of the deposited Ti-6Al-4V alloy with 0.05 wt% boron addition reached 1089 MPa, which was 17% higher than that of directly deposited Ti-6Al-4V alloy, and the elongation remained at 8% without significant reduction. The synergistic balance of strength and ductility was attributed to the grain refinement and cyclic gradient distribution of TiB whiskers. When the boron content was 0.15 wt%, the elongation of the deposited alloy was reduced to 5.2% though tensile strength reached 1178 MPa due to the formation of quasi-continuous TiB whiskers distributed along the prior β grain boundaries. Furthermore, the formation of heat-affected bands between the two adjacent layers of TiB-reinforced Ti-6Al-4V alloy was discussed based on the measurement of the thermal history during the additive manufacturing process and the part’s microstructure evolution.

Tribological characteristics of the dual titanium boride layers (TiB2+TiB) on titanium alloy

In this study, by producing the dual titanium boride (TiB2 +TiB) layers (DTBLs) on titanium alloy using solid-state boriding with rare earth additions (REs), the friction tests with two different counter-materials (GCr15 and Al2O3) were conducted. It is found that solid-state boriding of titanium alloy with REs can achieve better tribological properties than that of conventional one, without REs; furthermore, with the size of TiB whiskers decreasing, the tribological properties was further improved. To illustrate the size effect of TiB whiskers on the tribological properties, a novel surface uniaxial compression model of DTBLs was developed; then, a surface wear model using Archard wear equation was proposed to quantitatively estimate such size effect of TiB whiskers. It indicates that the above two models can adequately explain the mechanism of the size effect of TiB whiskers on the mechanical and tribological properties. The results of this study showed that the improvement of tribological performance of DTBLs was dominated not only by the “hard” TiB2 layer but also by the “soft” shear accommodating TiB layer; when the size of TiB whiskers is closed to the sub-micron scale, fine-grain strengthening effect would become obvious, causing the tribological properties further improved.

A novel Ti cored wire developed for wire-feed arc deposition of TiB/Ti composite coating

A novel Ti cored wire containing TiB2, Al60V40 and Ti6Al4V mixed powders was developed for wire-feed arc deposition of TiB/Ti composite coating, to enhance the hardness and wear resistance of Ti alloy. Results showed that after experiencing several chemical reactions, the wire was melted in the arc zone and turned into nonuniform droplets composed of Ti-Al-V-B melt and undecomposed TiB2 particles. With the increase of welding current, the detachment time of droplet shortened while the transfer frequency accelerated, accompanied by the improvement in coating surface quality. The spatial distribution of TiB whiskers in coating was governed by welding current. A uniform distribution could be achieved as welding current was sufficient at the expense of elevated dilution ratio, while increasing wire feeding speed could compensate the dilution loss of TiB whisker to some extent. The decomposition process of TiB2 particles and the microstructure evolution mechanism of coating was discussed in detail. The optimum coating possessed uniform microstructure, relatively low dilution ratio, and high hardness (639.1 HV0.5) as compared with Ti6Al4V substrate (326 HV0.5). Indentation morphology analysis verified the excellent performance was ascribed to the load-sharing strengthening of TiB whiskers. This study provides a high-efficiency fabrication method for the ever-developing titanium matrix composites (TMCs) coating.

Microstructure refinement and strengthening mechanisms of network structured TiBw/Ti6Al4V composites by TIG remelting

In order to further strengthen TiB whiskers reinforced Ti6Al4V (TiBw/Ti6Al4V) composites with a network microstructure, tungsten inert gas (TIG) remelting was performed on the composites with different reinforcement volume fractions to tune microstructure. The results showed that the size of network unit and TiB whisker reinforcement of the composites were significantly refined from 150 μm to 20 μm in diameter and 3 μm to 0.5 μm in width after remelting, respectively. Moreover, the α phase of Ti6Al4V matrix was transformed into a refined α′ phase due to the rapid air-cooling process. It is also revealed that the refinement of network microstructure was resulted from the hypoeutectic reaction of the Ti–B system. However, the network microstructure disappeared when the reinforcement volume fraction rises to 10 vol.%, and then coarse primary TiBw appeared when to 20 vol.%. After remelting, the hardnesses of 3.4 vol.%, 10 vol.%, 15 vol.% and 20 vol.% TiBw/Ti6Al4V composites were increased to HRC 36, HRC 40, HRC 43 and HRC 50 from HRC 32, HRC 37, HRC 40, HRC 47, respectively. The tensile strength at 600 °C was increased by 10%–20% while remaining the similar tensile ductility. The strengthening mechanisms can be mainly attributed to microstructure refinement and α’ martensite formation.

A study of the SiCf/SiC composite/Ni-based superalloy dissimilar joint brazed with a composite filler

Uniform and fine in-situ short-fiber/particle hybrid reinforcements were obtained in a SiCf/SiC composite/Ni-based superalloy joint by using a novel AuCuTiB/Mo/AuCuTiB composite filler. The growth of in-situ phases showed a strong dependence on the numbers of nucleation sites and metal atoms on the ceramic side. Inadequate brazing conditions adversely affected the formation of indirect TiB whiskers, and excessive brazing conditions induced an accumulation of metal atoms. As a result, the in-situ phases switched from Ti5Si3 + TiC to Ti5Si3 + Ni + TiB + TiC, and to (Ni, Ti)-(Si, C) + TiB with increasing brazing conditions. The size, type, and composition of the in-situ phases were effectively controlled by adjusting the brazing conditions (B content, brazing temperature, and holding time). In light of this, the shear strength of the joint was optimized at 124.9 MPa. The excellent mechanical performance was ascribed to (i) a suitable interfacial layer and (ii) the effective stress relief of in-situ phases and ductile/rigid/ductile multiple layers. Moreover, the joint exhibited mechanical stability at 973 K because the in-situ phases can serve as a high-temperature resistant second structure.

Spark plasma sintering of Ti6Al4V metal matrix composites: Microstructure, mechanical and corrosion properties

The aim of the present work is to study the synergistic effect of TiC particles (TiCp) and TiB whiskers (TiBw) reinforcement on titanium matrix composites (TMCs) fabricated by spark plasma sintering (SPS). The effect of reinforcement type and content on the microstructure and mechanical properties were investigated. Four different powder compositions were prepared by mixing TiC and B in the Ti6Al4V matrix powder. The reaction between boron and Ti resulted in in situ TiBw formation uniformly in the matrix whereas the TiC particles were accommodated at the grain boundaries. The individual contribution of both the reinforcement phases accredited to grain refinement, dispersion strengthening, and load distribution towards the final strengthening in composite was evident. An increase in both the mechanical and tribocorrosion properties was evident with TiC addition followed by a further improvement with B addition. Scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) analysis were used for confirming the grain refinement, whereas the phase determination was done using X-ray diffraction (XRD) analysis.

Microstructure evolution and tensile properties of as-rolled TiB/TA15 composites with network microstructure

To investigate the microstructure evolution and mechanical properties of DRTMCs with network microstructure during the rolling deformation, the TiB whiskers reinforced Ti-6.5Al–2Zr–1Mo–1V (TA15) composites (TiBw/TA15) with the addition of silicon element and different TiB volume fractions were successfully fabricated by hot pressing sintering and rolled in the α+β region. Compared with the as-sintered composites, the as-rolled composites presented the lower local TiBw content, higher matrix connectivity, remarkable grain refining and larger silicides. After rolling deformation, the room-temperature ultimate strength and fracture elongation were dramatically improved. The as-rolled 3.5 vol.% TiBw/TA15 composite obtained better combination properties of 1248 MPa and 10.5% at room temperature. The increase in strength can be attributed to grain refining of the matrix, directional distribution of TiBw, and stronger hinder of silicides. The enhancement of ductility was due to increasing matrix connectivity, grain refining as well as DRX behavior of bimodal microstructure. As for high-temperature properties, the tensile strengths increased by 26–32% at 600 °C and 20–32% at 650 °C after rolling, which is also attributed to directional distribution of TiBw, grain refining of matrix and larger silicides. The highest strengths at 600 °C and 650 °C are 820 MPa and 698 MPa, respectively. The fracture behavior of the composites was discussed in detail. • As-sintered and as-rolled TiBw/TA15 composites with excellent metallurgical bonding were achieved. • Room temperature strength and ductility of the composites were simultaneously improved a lot after rolling. • Flat network microstructure continued to exert the reinforcement and strain bearing of bi-connected structure after rolling. • TiB rotation, larger silicides and refined grains during rolling deformation contribute to the strength enhancement.

Microstructure and superior mechanical property of in situ (TiBw + TiCp)/Ti composites with laminated structure

The strength and ductility of titanium matrix composites (TMCs) hardly co-exist and show a trade-off between each other. In order to balance the strength and ductility of TMCs, in situ TiB whiskers (TiBw) and TiC particles (TiCp) strengthened Ti composites with laminated structure were constructed via electrophoretic depositing (EPD) boron (B) powders + graphene oxides (GOs) on pure Ti foils followed by spark plasma sintering (SPS). The experiment results reveal that increasing EPD duration leads to more synthesized TiBw + TiCp reinforcements accompanied by decreased grain size of Ti matrix in the sintered composites, which favorably results in gradually enhanced strength. A maximum yield strength (YS) of 569 MPa is achieved in the laminated composite, which is 75.6% higher than that of pure Ti sample (YS: 324 MPa). Meanwhile, the composite still owns a relatively higher elongation of 12.0%. The achievement of good ductility should benefit from the laminated architecture which exerts constraint effect on crack propagation. This work provides a short cut to achieve strength-ductility synergy in TMCs.

Thermomechanical Processing of a Near-α Ti Matrix Composite Reinforced by TiBw.

To further improve the mechanical properties of the as-cast 7.5 vol.% TiBw/Ti–6Al–2.5Sn–4Zr–0.7Mo–0.3Si composite, multi-directional forging (MDF) and subsequent heat treatments were carried out to adjust TiB whiskers (TiBw) and matrix characteristics. The effect of various microstructures on the tensile properties and fracture toughness of the composites was analyzed in this paper. After MDF, the TiBw are broken into short rods with a low aspect ratio and display a random distribution. Moreover, distinct microstructures were obtained after thermomechanical processing and different heat treatments. Both room-temperature and high-temperature tensile strength and ductility are improved after thermomechanical processing. By increasing the solution-treatment temperature, the microstructures transform from equiaxed to fully lamellar. A simultaneous improvement of the room-temperature and high-temperature properties is associated with the microstructural changes. In addition, the fracture toughness exhibits an increasing trend as the volume fraction of equiaxial α phases decreases. The lamellar microstructure demonstrates excellent fracture toughness due to deflection of the crack propagation path.

Microstructure evolution and mechanical properties of in-situ Ti6Al4V–TiB composites manufactured by selective laser melting

In-situ TiB reinforced titanium matrix composites (TMCs) were fabricated by selective laser melting (SLM) of ball-milled Ti6Al4V–TiB2 powders. Optimized SLM processing and stress relief annealing were applied to obtain crack-free and fully dense composites. TiB reinforcement is mainly present in the form of whisker clusters and exhibits a quasi-continuous distribution in TMC1 (2 vol%TiB) while a full-continuous distribution in TMC2 (5 vol%TiB). The distribution of TiB whisker clusters in primary β-Ti grain is not consistent with the complete dissolution mechanism proposed previously. As a result, a dual mechanism of direct reaction and precipitation has been put forward to describe the formation of TiB phase. The microhardness, compressive strength and tensile strength of TMC1 are improved by 14%, 36%, 25% respectively, compared with those of Ti6Al4V alloy. These enhancements can be mainly attributed to Hall-Petch strengthening and load-bearing transformation strengthening. The fracture surface of TMC1 after tensile testing shows a mixture of regions of cleavage facets with regions of small dimples.

Characterization of Boride Layer Formed on Ti–6Al–4V Alloy by Electron Beam Evaporation Technique

Ti–6Al–4V alloy was borided by using a two-stage boriding process. In the first stage, boron atoms accumulated on Ti–6Al–4V alloy samples via electron beam evaporation technique. The second stage included annealing of samples after boron deposition at various temperatures in order to achieve boride layer with high hardness and adherence. After the boriding treatment, phases formed on the surface of the Ti–6Al–4V alloy were identified by X-ray diffraction technique. The microstructure and thickness of boride layers were examined by scanning electron microscope. Microstructural analyses indicated that surface structure of borided samples comprised of TiB2 layer on the top and TiB whiskers towards the substrate. It was revealed that boriding by electron beam evaporation technique resulted in formation of a hard and adhered surface structure after annealing especially at 950°C for 24 h. Microhardness measurements showed that boride layer on Ti–6Al–4V has mean hardness value of about 1937 HV. Boriding at 950°C for 24 h brought about an improvement in wear resistance of Ti–6Al–4V alloy. The borided surface exhibited higher wear resistance along with higher coefficient of friction as compared to as-received one.