The study of powder metallurgy processing methods for titanium represents a promising avenue that can respond to a growing demand. This work reports the feasibility of direct powder forging (DPF) as ...a method to process large spherical Ti-6Al-4V powder into wrought products with noteworthy properties and physical characteristics. Direct powder forging is a thermomechanical process that imparts uniaxial loading to an enclosed and uncompacted powder to produce parts of various sizes and shapes. Stainless steel canisters were filled with prealloyed Ti-6Al-4V powder and consolidated through a multi-step open-die forging and rolling process into wrought DPF bars. After DPF, annealing was performed in the upper α+β phase. The results show that full consolidation was achieved and higher mechanical properties than the Ti-6Al-4V grade F-23 requirements in annealed conditions were obtained. The results also show that direct powder forging of spherical titanium powder could produce wrought mill products and exhibit some potential for further investigation for industrial applications.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In this paper, we report the first hydrogenation (activation) of a 1.2Ti-0.8Fe alloy synthesized by induction melting (9 kg ingot). The alloy presented a three-phase structure composed of a main TiFe ...phase, a secondary Ti2Fe phase and a Ti-rich BCC phase. The alloy required cold rolling to achieve activation at room temperature. However, it did so with good kinetics, reaching saturation (2.6 wt.% H) in about 6 h. After activation, the phases identified were TiFe, Ti2FeHx and an FCC phase. The Ti2FeHx and FCC are the stable hydrides formed by the secondary Ti2Fe and BCC phases, respectively. The stoichiometry of the Ti2FeHx was calculated to be between x = 3.2–4.75. As the microstructure obtained by an industrial-scale synthesis method (induction melting) may be different than the one obtained by laboratory-scale method (arc melting), a small 3 g sample of Ti1.2Fe0.8 was synthesized by arc melting. The lab-scale sample activated (2 wt.% H in ~12 h) without the need for cold rolling. The phases identified for the lab-scale sample matched those found for the induction-melted sample. The phase fractions differed between the samples; the lab-scale sample presented a lower abundance and a finer distribution of the secondary phases. This explains the difference in the kinetics and H capacity. Based on these results it can be concluded that the alloy of composition, 1.2Ti-0.8Fe, can absorb hydrogen without the need for a heat treatment, and that finer microstructures have a strong influence on the activation kinetics regardless of the secondary phases’ phase fractions.
This study investigates direct powder forging (DPF) as a new approach for near-net-shape processing of titanium alloys using a coarse particle size distribution (PSD) between 90 and 250 μm. This ...route was utilised to takes advantage of DPF’s enclosed nature to make near-net-shape components with conventional forging equipment, making it attractive and viable even for reactive powder such as titanium. In this study, the uncompacted Ti-6Al-4V ELI powder was sealed under vacuum in a stainless-steel canister and hot forged in air to produce a fully dense titanium femoral stem. After the final forging stage, the excess material in the flash region was cut, which efficiently released the canister, revealing the forged part with minimal surface contamination. The as-forged microstructure comprises coarse β grains with a martensitic structure. The subsequent annealing was able to generate a fine and homogenous lamellar microstructure with mechanical properties that respects the surgical implant standard, showing that DPF offers significant potential for forged titanium parts. Therefore, the DPF process provides a suitable alternative to produce titanium components using basic equipment, making it more available to the industry.
In this work, the hydrogen storage behavior of Ti2CrV + X wt.% Zr3Fe, where X = 2, 4, 6, 8 and 10 was investigated. The synthesis of all samples was carried out through arc-melting, followed by ...comprehensive characterization using X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The pure-Ti2CrV as-cast sample presented a single-phase microstructure. However, the addition of the Zr3Fe led to a remarkable transformation, resulting in the appearance of a Zr-rich secondary phase. It was found that the first hydrogenation is improved with the addition of at least 6 wt% of Zr3Fe, avoiding any preheating of the sample. These samples achieved their maximum capacity in approximately 10 min at room temperature. The maximum capacity recorded was 4.2 wt% H for the sample with X = 6 wt% Zr3Fe, while for X = 8 and 10 wt% Zr3Fe, the capacity recorded was 4.1 wt% and 4.0 wt%, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Chemically homogenous, fully dense and highly spherical Ti-5Fe powder prepared by EIGA.•Similar PSD and oxygen pick-up as the conventional Ti-6Al-4 V.•The Omega phase is present with a minor alpha ...phase resulting from the high cooling rate.
This study demonstrated the viability of the electrode induction gas atomization process (EIGA) to produce spherical Ti-5Fe powder suitable for additive manufacturing. The resulting powder is spherical and presents no surface defects. Additionally, the iron distribution throughout the microstructure is homogenous and indicates similar particle size distribution and oxygen pick-up as the conventional Ti-6Al-4V titanium alloy, thus demonstrating that the Ti-5Fe can achieve equal atomization behavior and powder outcome. The results of the study show how EIGA-type gas atomization can be an efficient scale-up route to produce Ti-5Fe low-cost titanium alloy powder for additive manufacturing, which offers a broader perspective into biomaterial application.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The effect of the substitution of Ti by Zr on the crystal structure, microstructure, and first hydrogenation behavior of Ti2-xZrxCrV where X = 0.5, 1.0, 1.5, and 2.0 have been investigated. The ...samples were synthesized by arc-melting and characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The hydrogenation capacity was measured using a home-made Sieverts apparatus. Pure-Ti2CrV crystallizes in a body-centered cubic structure (BCC). Substitution of Ti by Zr leads to the appearance of a secondary phase, namely a C15 Laves phase for the Ti-containing samples, and C15 Laves phase plus a Zr-rich phase for the X = 2.0 sample. The substitution of Ti by Zr increased the lattice parameters in both phases for all samples. Increasing Zr content made the first hydrogenation faster but reduced the hydrogen capacity.
•The effect of the substitution of Ti by Zr in the Ti2-xZrxCrV alloy was investigated.•Substitution of Ti by Zr leads to the appearance of a secondary phase, namely a C15 Laves phase.•The first hydrogenation was enhanced, without pre-heat treatment.•The maximum hydrogen storage capacity registered reached 3.5 wt% H at room temperature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, a modification of the microstructure of a commercial Ti-6Al-7Nb alloy was accomplished by high-pressure torsion (HPT) at room temperature, to produce a bulk nanostructure on discs of 10 ...mm diameter and ∼0.8 mm thickness. The metallographic analyses of the discs were
performed by optical microscopy and scanning electron microscopy with energy dispersive spectroscopy. The results confirmed the presence of aluminum (Al) and niobium (Nb) as the sole alloying elements, promoting a duplex (α + β) titanium (Ti) microstructure prior to HPT processing.
After HPT processing, nanostructure refinement was attained, reflected in the X-ray diffraction profiles as broadening of the α-Ti and β-Ti peaks and the appearance of the ω-Ti phase. Transmission electron microscopy confirmed a grain size < 100 nm after HPT processing
for N = 5 revolutions. Microhardness increased significantly with straining by HPT, which can be attributed both to the grain refinement and the formation of the ω-Ti phase.
This study investigates direct powder forging (DPF) as a new approach for the consolidation and in-situ alloying of the titanium alloy Ti-5Fe from loose powder. The absence of green compaction before ...thermomechanical processing and the effect of the powder blending method have been found to significantly influence the chemical and microstructure homogeneity. Two different powder mixing techniques were compared, ball milling (BM) and blended elemental (BE). After the initial heating stage, the BM sample has a uniform α+β lamella microstructure within the particles with a homogeneous iron distribution, unlike the BE sample, which shows a heterogeneous lamella microstructure, retained β-Ti (Fe-rich) and TiFe intermetallic compounds. Even if the BM samples exhibit a slightly higher density over the BE samples after the initial heating stage, all samples achieved full density and had a α+β lamella microstructure after the thermomechanical steps. However, for the BE sample, even if the DPF process was able to eliminate the intermetallic compounds, the thermomechanical process did not homogenize the iron, resulting in a heterogeneous and coarser microstructure. Based on the results, it can be concluded that DPF using a BM technique led to a fully homogenous and fully consolidated Ti-5Fe alloy. Therefore, direct powder forging has significant potential as an alternative fabrication strategy to produce the Ti-5Fe alloy. Moreover, this work can expand the opportunities for the development of the promising Ti-5Fe alloy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microstructural modifications of a biomedical Ti-6Al-7Nb alloy were accomplished via heat treatment in 3 different quenching mediums and then processed by High-Pressure Torsion (HPT) at room ...temperature. The microstructure of the as-received condition is composed of an equiaxed duplex (α+β) structure. After the heat treatment, a combination of primary α phase and lamellar structures was obtained with an increasing fraction of the martensitic lamellar with increasing cooling rate. After HPT processing, refinement of the microstructures was observed for N=5 revolutions. Transmission electron microscopy (TEM) of the sample quenched in liquid nitrogen confirmed the nanostructure with grain sizes below 100 nm and high density of lattice defects after HPT processing for N=5 revolutions. High-temperature tensile tests were carried out at 800 °C with an initial strain rate of 2×10−3 s−1 on specimens with different combinations of heat treatment and HPT straining. The test in the as-received condition presented a maximum elongation to failure of ~400% after HPT processing for N=5 revolutions. The highest elongation to failure in the heat-treated samples was ~580% in the sample quenched in liquid nitrogen and processed for N=5 revolutions.
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