Spherical Ti Powders Research Articles

Pressure-less melt infiltration characteristics of Mg melt into Ti powder preforms with various pore structures: Toward the application to the binder jetting additive manufacturing

Binder jetting (BJT) additive manufacturing enables the fabrication of complex-shaped metallic parts but requires sintering as post-processing to obtain dense parts. The sintering inevitably causes the shrinkage from green body to dense products, resulting in low dimensional accuracy. In contrast, pressure-less melt infiltration (PMI) fills pores in the green body with a liquid metal driven by capillary pressure and fabricates a dense metal matrix composite without severe shrinkage. To consider the applicability of pressure-less melt infiltration to the post-processing of binder jetting additive manufacturing, it is required to clarify the relationship between pressure-less melt infiltration process conditions and the relative density of the composites. In this study, the liquid Mg/solid Ti system was selected because of good wettability and absence of Mg-Ti intermetallic, and the conditions of Ti powder preforms (corresponding to the green body) were focused on. Ti powder preforms with various powder sizes (2300, 410, 140, and 20 μm) and different shapes (irregular and spherical) were cold-pressed at 76, 102, 127, 153, and 178 MPa to fabricate preforms with various relative densities, pore sizes, and pore morphologies to response the similar characteristics in BJT preforms. Mg melt infiltrated into the preforms under constant conditions to fabricate Mg/Ti composites. The structures of the preforms and composites were characterized by sample size measurement, optical and scanning electron microscopy, and X-ray computed tomography. It was revealed that the relative density of the composite increased with decreasing Ti powder size and using spherical Ti powder, whereas the compact pressure exhibited a slight effect. Furthermore, defect volume increased with increasing infiltration height but decreased around the top surface of the sample. Minute observations around defects in the composites revealed that defects were formed at larger pores, and Mg melt was infiltrated into pores above the defects. These results indicated that infiltration velocity varied depending on the flow channel structure, and gas was trapped at larger pores (far from the outside of the sample) where infiltration velocity was low. Using smaller Ti powder decreased the variation in pore size in the preform, resulting in improving the relative density of the composites by suppressing the gas trapping. This study provides a new insight into the pressure-less melt infiltration process as a post-processing of binder jetting additive manufacturing.

First principles study of Ti-Zr-Ta alloy phase stability and elastic properties

The effects of Ta and Zr content on the stability, elastic properties and electronic structure of Ti-Zr-Ta alloy phase were studied by first principles calculation method based on density functional theory. Moreover, Ti-Zr-Ta alloy was fabricated by spark plasma sintering (SPS) using spherical Ti powder,Ta powder, and Ti-Zr-Ta alloy powder produced by the plasma rotation electrode process (PREP). Afterward, the effects of sintering temperature, Zr and Ta content on the microstructure and mechanical properties of the alloy samples were investigated. The results showed that sintering temperature, Ta and Zr content were the key factors which affected the densification. When the sintering temperature was raised, the relative density and mechanical properties of Ti-Zr-Ta alloy were significantly increased. The first- principles calculation also indicated that Ti-1Zr-Ta possesses the lowest Young’s modulus and the best ductility, showing great potential of biomedical applications which agrees with the results of experimental results of alloy preparation.

Microstructure and Mechanical Properties of Core-Shell B4C-Reinforced Ti Matrix Composites.

Composite material uses ceramic reinforcement to add to the metal matrix to obtain higher material properties. Structural design is an important direction of composite research. The reinforcement distribution of the core-shell structure has the unique advantages of strong continuity and uniform stress distribution. In this paper, a method of preparing boron carbide (B4C)-coated titanium (Ti) powder particles by ball milling and preparing core-shell B4C-reinforced Ti matrix composites by Spark Plasma Sintering was proposed. It can be seen that B4C coated on the surface of the spherical Ti powder to form a shell structure, and B4C had a certain continuity. Through X-ray diffraction characterization, it was found that B4C reacted with Ti to form layered phases of titanium boride (TiB) and titanium carbide (TiC). The compressive strength of the composite reached 1529.1 MPa, while maintaining a compressive strain rate of 5%. At the same time, conductivity and thermal conductivity were also characterized. The preparation process of the core-shell structure composites proposed in this paper has high feasibility and universality, and it is expected to be applied to other ceramic reinforcements. This result provides a reference for the design, preparation and performance research of core-shell composite materials.

A method for the preparation of spherical titanium powder for additive manufacturing

In this work, a new method was designed and developed to produce spherical Ti powder for additive manufacturing (AM) process. In this method, copper was introduced to form Ti-Cu alloy with a low melting point, and spherical Ti powder was prepared by combining with several low-cost processing techniques, including solid-liquid interface dewetting spheroidization, dealloying, sintering and de‑oxygenation processes. The spherical Ti powder prepared by this method shows a low oxygen content (<0.1 wt%), and the particle size was controlled between 15 and 75 μm. Compared with the current mature technology of the preparation of spherical titanium powder, this method provideds unique advantages during the preparation of small-sized spherical Ti powder (<30 μm), which meets the requirements of high-quality AM technology. • A new method was designed and developed to produce spherical Ti powder. • Techniques and raw materials are low cost. • Spherical Ti powder with controllable size distribution and low oxygen content can be produced.

Effect of Powder Particle Size and Shape on Appearance and Performance of Titanium Coatings Prepared on Mild Steel by Plasma Cladding

The preparation of Ti coatings on mild steel can both effectively improve the corrosion resistance of the substrate and reduce the application cost of Ti, which is an effective measure to improve the service performance of mild steel in the marine environment. Plasma cladding technology is an efficient method for preparing metal coatings, and the type of powder is a key process parameter for coating preparation. In this work, high-performance Ti coatings are prepared on the surface of mild steel by plasma cladding technology, and the effects of different particle sizes and shapes of Ti powders on the surface morphology, microstructure and properties of the coatings are studied. The results show that powder particle size and sphericity are the key factors affecting the morphology, structure and service performance of Ti coatings. After 1000 h of salt spray test, the spherical powder cladding coatings only suffer slight corrosion, while the irregular shape powder coating is more severely corroded. Powder cladding with moderate powder particle size and good sphericity have a smoother coating and fewer defects. Ti powders with different particle sizes and shapes all have the diffusion of Fe element during the cladding process. The surface of Ti coating prepared by spherical powder are dominated by α-Ti and Fe0.2Ti0.8 phases, while the surface of Ti coating prepared by irregular shape powder is dominated by FeTi and Ti2Fe. The interface between the coating and the substrate shows metallurgical bonding, and the increase in Ti-Fe brittle phase will deteriorate the mechanical properties and corrosion resistance of the coating. The shear strength of coatings prepared from spherical Ti powders of 75–150 μm can reach 105.18 MPa, the corrosion potential is the most positive (−0.2206 V), and the self-corrosion current density is the lowest (6.220 × 10−8 A/cm2).

Micropatterning of synthetic diamond by metal contact etching with Ti powder

Due to the high hardness and chemical stability of diamond, micropatterning of diamond surfaces is a manufacturing challenge that limits the wide application of diamond. In this paper, uniformly distributed micropatterns were produced on the surface of synthetic diamond by metal contact etching of spherical Ti powder. The effects of spherical Ti powder particle size and etching temperature on the size and depth of the micropatterns were investigated. The results showed that the proportion of the patterned area on the diamond surface decreased with the particle size increase of spherical Ti powder. However, the size and depth of the micropatterns increased. In addition, both of the pattern area proportion of the diamond surface and the size and depth of the micropatterns increased with the rise of etching temperature. Importantly, diamond etching was achieved using Ti powder without appearance of graphitization of the diamond. This work is of significance for the customization of micropatterns on diamond surface and can further expand the application of diamond.

Effect of Radiofrequency Plasma Spheroidization Treatment on the Laser Directed Energy Deposited Properties of Low-Cost Hydrogenated-Dehydrogenated Titanium Powder.

Titanium for additive manufacturing presents a challenge in the control of costs in the fabrication of products with expanding applications compared with cast titanium. In this study, hydrogenated–dehydrogenated (HDH) titanium powder with a low cost was employed to produce spherical Ti powder using the radiofrequency plasma (RF) technique. The spherical Ti powder was used as the raw material for laser directed energy deposition (LDED) to produce commercially pure titanium (CP-Ti). Microstructural analyses of the powder revealed that RF treatment, not only optimized the shape of the titanium powder, but also benefited in the removal of the residual hydride phase of the powder. Furthermore, the LDED-HDH-RF-produced samples showed an excellent combination of tensile strength and tensile ductility compared to the cast and the LDED-HDH-produced samples. Such an enhancement in the mechanical properties was attributed to the refinement of the α grain size and the dense microstructure. The present work provides an approach for LDED-produced CP-Ti to address the economic and mechanical properties of the materials, while also providing insights into the expanding application of HDH titanium powder.

Novel fabrication of low-cost Ti–Cu alloy by electroless copper plating and vacuum sintering

We report a novel fabrication method of low-cost Ti–Cu alloy. Cu coated Ti powders with core-shell structure are prepared by electroless copper plating of spherical Ti powders. The growth mechanism of core-shell Ti@Cu powders is illustrated. The sintered Ti–Cu alloy exhibits excellent mechanical properties due to the homogeneous distribution of the fine Ti2Cu particles in the Ti matrix after sintering treatment.

Development of core–shell-structured Ti-(N) powders for additive manufacturing and comparison of tensile properties of the additively manufactured and spark-plasma-sintered Ti-N alloys

In this study, Ti-(N) powders with a core–shell structure were prepared via a nitriding process of titanium (Ti) powders for metal additive manufacturing (AM). Nitriding of spherical Ti powders (D50=130 µm and D50=63 µm) was carried out at different temperatures from 873 K to 1373 K for 10 min. The nitriding process enabled the manufacture of a core–shell-structured Ti-(N) powder, where an N-enriched shell surrounds a lower N core. The thickness of the N-rich Ti shell increases exponentially with increasing nitriding temperature. Depending on nitriding temperature, a shell layer consisting of Ti2N and TiN compounds can form. Based on X-ray diffraction (XRD) results, it was identified that the N-rich shell is composed of (i) only Ti(N) solid solution when nitrided below 1023 K; and (ii) Ti(N) solid solution, Ti2N and TiN compounds if nitrided at or above 1023 K. The core–shell-structured Ti-(N) powders were subsequently used to manufacture bulk samples by spark plasma sintering (SPS) and laser metal deposition (LMD) processes for comparison. The microstructure was characterized and discussed. LMD-fabricated Ti-N alloy samples exhibited high tensile strength (965 MPa) with good tensile ductility (7.6%) due to the homogeneous distribution of N and fine grain size. In contrast, SPS-fabricated Ti-N alloy samples using the same nitrided Ti-N powder showed much lower tensile strength (708 MPa) with essentially no tensile ductility (0.3%) due to the inhomogeneous distribution of N. LMD can allow the fabrication of strong and ductile Ti-N alloys while it is not possible by SPS.

High-performance titanium-based composite strengthened with in-situ network-distributed 3D reinforcements

Ti-based composite with in-situ 3D nano-reinforcements consisted of boron nitride nanosheets (BNNSs), titanium boride (TiB) nanowires and titanium diboride (TiB2) nanoparticles was prepared in a facile way—blending spherical Ti powder and BNNSs via low-energy ball milling and then consolidating the composite powder by spark plasma sintering. It has an excellent combination of strength and ductility: the composite with 0.5 vol% BNNSs exhibits high tensile strength of around 715.1 MPa and excellent toughness of 115.2 MJ/m3, which is 73.4% higher and 16.6% lower than those of pure Ti, respectively. The strength enhancement is mainly attributed to the interlocking structure formed by TiB2 nanoparticles and BNNSs, which increases the dislocation density and doubles the theoretical interfacial shear strength limit. The considerable ductility arises from the crack blocking brought by the 3D network.

A Sustainable Approach for Producing Ti and TiS2 from TiC

TiC was examined as a starting material for Ti metal production by sulfidation and electrochemical reduction in molten salt. The sulfur evaporation temperature, sulfidation temperature, and time were optimized in a dual-zone furnace for the efficient and sustainable formation of TiS2 as well as carbon removal from TiC by S2 gas sulfidation. A mixture of TiS2 and Ti2.45S4 powders was synthesized from TiC at 1200 °C, and a perfect carbon removal was achieved to a very clean level as low as 0.025 mass pct C. The sulfides derived from TiC were then electrochemically reduced in molten CaCl2-0.5 mol pct CaS salt. The spherical shape Ti powder consisting of high-purity Ti sheets was obtained from TiS2 without the carbon contamination. This method might be applied for sustainable recycling of waste carbides and for production of low-cost Ti powders via TiC or TiOxCyNz from the titanium ore.

Size effect of flake Ti powders on the mechanical properties in graphene nanoflakes/Ti fabricated by flake powder metallurgy

The effect of the size of the flake Ti powders on fabricating graphene nanoflakes (GNFs)/Ti composites were investigated in this work. By this, the flake Ti powders of various size were produced via the flake powder metallurgy methods. The GNFs were tightly inserted into the flake Ti powders during high energy ball milling (HEBM) process. Raw spherical Ti powders (45 μm) with 4.34 deformation degree exhibit the best GNFs distribution on boundaries and in the interior of grains. Thus, after a short time heat treatment, the exceptional network-structural GNFs/Flake Ti properties were achieved with a good ductility and a superior compressive strength of ∼2.8 GPa. It was demonstrated that the excellent properties were mainly attributed to the proper combination of special distribution status and effective load transfer ability of titanium carbide interface. The results might provide new insights for designing advanced GNFs/Fake Ti composites with simultaneously high strength and ductility.

Surface characterization and formation mechanism of the ceramic TiO2-xNx spherical powder induced by annealing in air

Mechanism for the formation of titanium oxynitride (TiO2-xNx) on the surfaces of spherical Ti powder particles upon heat treatment in air at 500, 600, 700 and 800 °C was investigated. The results showed that the first at 500 °C a hexagonal closed packed (HCP) TiOx film was formed while aTiO2 film was observed after annealing at 600 °C and eventually a TiO2-x-Nx layer coated the spherical Ti particles at 700 and 800 °C due to N diffusion within the TiO2 crystal lattice. The resulting surface structure was studied by means of x-ray diffraction (XRD) while the surface morphology of the powders was characterized using the scanning electron microscope (SEM) attached with energy dispersive x-ray spectroscopy (EDS) detector. The AFM images confirmed that when the N content increases (800 °C-heat treated sample) the powder loses its triangular grains (700 °C-annealed sample) to irregular shaped grains.

Synthesis of TiC reinforced Ti matrix composites by spark plasma sintering and electric discharge sintering: A comparative assessment of microstructural and mechanical properties

Ti-TiC composite materials were produced by spark plasma sintering (SPS) and electric discharge sintering (EDS) of spherical Ti powders with surface-embedded TiC. Hardness (HIT) and reduced elastic modulus (Er) were estimated using the nanoindentation method with an applied load of 100 mN, and compared with the micro-Vickers hardness value. The microstructure of SPS composite compacts revealed that the TiC particles were uniformly distributed only along the Ti particle boundary. On the other hand, for the EDS composite compacts, the strip-like TiC particles of 1–2.5 µm in size were homogeneously dispersed in the Ti matrix, indicating that the discontinuous and randomly orientated TiC can more efficiently impede the plastic flow of the matrix phase of Ti. The micro-Vickers and nanoindentation hardness for the SPS composite compacts slightly increased with increased TiC content from 0 to 20 wt%, the increments of which were about 67 Hv and 0.7 GPa, respectively. Meanwhile, the EDS composite compacts exhibited significantly higher micro-Vickers and nanoindentation hardness with the increment of 653 Hv and 6.5 GPa, respectively. This result was ascribed to the TiC particles uniformly dispersed across the Ti matrix. Accordingly, the ratio values, such as HIT/Er and HIT3/Er2, were also significantly higher for the EDS composite compacts at all the range of TiC content due to stiffening and hardening effects derived from the TiC reinforcement. Therefore, the better incorporation of the TiC in the Ti matrix significantly improved the hardness and wear properties of the Ti composite reinforced with TiC produced by EDS compared with the SPS process.

Ultra-low cost Ti powder for selective laser melting additive manufacturing and superior mechanical properties associated

One of the bottleneck issues for commercial scale-up of Ti additive manufacturing lies in high cost of raw material, i.e. the spherical Ti powder that is often made by gas atomization. In this study, we address this significant issue by way of powder modification & ball milling processing, which shows that it is possible to produce printable Ti powders based on ultra-low cost, originally unprintable hydrogenation-dehydrogenation (HDH) Ti powder. It is also presented that the as-printed Ti using the modified powder exhibits outstanding mechanical properties, showing a combination of excellent fracture strength (~895 MPa) and high ductility (~19.0% elongation).

Microstructure and Mechanical Properties of Ti-6Al-4V Fabricated by Selective Laser Melting of Powder Produced by Granulation-Sintering-Deoxygenation Method

Commercial spherical Ti powders for additive manufacturing applications are produced today by melt-atomization methods at relatively high costs. A meltless production method, called granulation-sintering-deoxygenation (GSD), was developed recently to produce spherical Ti alloy powder at a significantly reduced cost. In this new process, fine hydrogenated Ti particles are agglomerated to form spherical granules, which are then sintered to dense spherical particles. After sintering, the solid fully dense spherical Ti alloy particles are deoxygenated using novel low-temperature deoxygenation processes with either Mg or Ca. This technical communication presents results of 3D printing using GSD powder and the selective laser melting (SLM) technique. The results showed that tensile properties of parts fabricated from spherical GSD Ti-6Al-4V powder by SLM are comparable with typical mill-annealed Ti-6Al-4V. The characteristics of 3D printed Ti-6Al-4V from GSD powder are also compared with that of commercial materials.

Review of the Methods for Production of Spherical Ti and Ti Alloy Powder

Spherical titanium alloy powder is an important raw material for near-net-shape fabrication via a powder metallurgy (PM) manufacturing route, as well as feedstock for powder injection molding, and additive manufacturing (AM). Nevertheless, the cost of Ti powder including spherical Ti alloy has been a major hurdle that prevented PM Ti from being adopted for a wide range of applications. Especially with the increasing importance of powder-bed based AM technologies, the demand for spherical Ti powder has brought renewed attention on properties and cost, as well as on powder-producing processes. The performance of Ti components manufactured from powder has a strong dependence on the quality of powder, and it is therefore crucial to understand the properties and production methods of powder. This article aims to provide a cursory review of the basic techniques of commercial and emerging methods for making spherical Ti powder. The advantages as well as limitations of different methods are discussed.

Surface Modification of Self-Consolidated Microporous Ti Implant Compacts Fabricated by Electro-Discharge-Sintering in Air

AbstractA single pulse of 0.75-2.0 kJ/0.7g of atomized spherical Ti powders from 300 mF capacitor was applied to produce a microporous Ti implant compact by electro-discharge-sintering (EDS). A solid core in the middle of the compact surrounded by a microporous layer was found. X-ray photoelectron spectroscopy was employed to study the surface characteristics of the EDS Ti compact and it revealed that Ti, C and O were the main constituents on the surface with a smaller amount of N. The surface was lightly oxidized and was primarily in the form of TiO2resulting from the air oxidation during EDS processing. The lightly oxidized surface of the EDS compact also exhibited Ti nitrides such as TiN and TiON, which revealed that the reaction between air constituents and the Ti powders even in times as short as 128 msec.

공극률에 따른 다공성 타이타늄 임플란트의 기계적 특성

Purpose: This study was performed to investigate mechanical properties of the porous Ti implants according toporosity. Porous Ti implant will be had properties similar to human bone such as microstructure and mechanicalproperties.Methods: Porous Ti implant samples were fabricated by sintering of spherical Ti powders(below 25 ㎛, 25~32 ㎛,32~38 ㎛, and 38~45 ㎛) in a high vacuum furnace. Specimen’s diameter and height were 4 ㎜and 40 ㎜. Surfaceand sectional images of porous Ti implants were evaluated by scanning electron microscope(SEM). Porosity andaverage pore size were evaluated by mercury porosimeter. Young’s modulus and tensile strength were evaluated byuniversal testing machine(UTM).Results: Porosity of Implant was increased according to larger particle size of the powder. Boundary portions ofparticles are sintered fully and others portions were formed pore. Young’s modulus was decreased by formed porousstructure. Tensile strength was decreased according to larger the particle size of the powder, but higher than humanbone.Conclusion: If prepared by adjust the porosity of the porous Ti implant will be able to resolve the stress shieldingphenomenon.

Self-consolidation mechanism of porous-surfaced Ti implant compacts induced by electro-discharge-sintering of spherical Ti powders

Porous-surfaced Ti implant compacts, with a solid core surrounded by a porous layer, were self-assembled by electro-discharge-sintering directly from spherical Ti powders. During an electro-discharge, instant high temperatures through the Ti powder column ranged from 1093 to 4925 °C were generated in times as short as 86–153 µsec. At the same time, pinch pressures ranging from 11 to 38 MPa were applied, especially to the middle of the Ti powder column. The solid core size depended on both the pinch pressure magnitude and the heat generated during a discharge. Both the pinch pressure (to squeeze and deform Ti powder particles), and the heat (to weld them together), were key factors in the production of porous-surfaced Ti implant compacts. It is thus suggested that the input energy at constant capacitance is a controllable electro-discharge parameter affecting the porosity and strength of the porous-surfaced Ti implant compacts.