Fe-Ti Alloys Research Articles

Degradation and recovery properties in thermochemical hydrogen compression by using TiFe alloy

The thermochemical hydrogen compression properties and cyclic durability of titanium-iron (TiFe) alloy were investigated at various temperatures of 200, 300, 450, and 500 °C by examing the achieved maximum pressure variations and hydrogen storage capacity before and after compression cycles. The cyclic durability of the TiFe alloy-based thermochemical hydrogen compressors was different depending on the operating temperature. Below 350 °C, the TiFe alloy-based hydrogen compressors showed stable thermochemical hydrogen compression properties with constantly achieved hydrogen compression pressure, hydrogen storage capacity, and unchanged phases. On the contrary, the reached maximum pressure with heating was gradually decreased during the compression cycles at 450 and 500 °C, suggesting poor durability and degradation at the higher temperature region. During the cycles, lattice strain and dislocation density of the alloy may be induced and lead to increase plateau pressure (hysteresis) without a change in hydrogen storage capacity. However, temperature increase can cause the disproportionation of TiFe around the formed lattice strain and dislocation. Therefore, after cycles at 500 °C, the hydrogen storage capacity is reduced by 30.4%. Furthermore, phase identification by X-ray diffraction measurements and thermal analysis suggested that TiH2, Fe2Ti, and Ti2Fe phases were disproportionately generated from the initial TiFe phase as irreversible hydrogen absorption states and became the dead volume for the cyclic compression cycles. Interestingly, the recovery of the TiFe alloy phase from the disproportionated phase of TiH2, Fe2Ti, and Ti2Fe can be achieved based on the TG-DTA-MS results. Therefore, based on the above results, the degradation and recovery properties in thermochemical hydrogen compression by using TiFe alloy are well understood in this work.

The mechanistic role of Ti4Fe2O1-x phases in the activation of TiFe alloys for hydrogen storage

TiFe alloy is considered an excellent candidate for stationary hydrogen storage owing to its superior hydrogen storage properties. However, the requisite for activation at high temperatures has hindered the practical application of TiFe alloy for hydrogen storage. This work investigates the activation of TiFe alloys with different Ti/Fe ratios. Results show that the TiFe0.90 alloy can be activated at room temperature and moderate hydrogen pressure (80 bar) compared to the poor activation kinetics of equimolar TiFe alloy. Microstructural characterization and surface analysis indicate that a higher content of Ti4Fe2O1-x phase formed in the TiFe0.9 alloy than in the TiFe0.95 and TiFe alloys. The embedded Ti4Fe2O1-x phase in the TiFe matrix plays a critical role in the overall activation processes, which serves as a conduit for hydrogen to interact with TiFe when it cracks during the initial stage of hydrogenation. The activation behavior is described in the following steps: (1) hydrogen absorption by the Ti4Fe2O1-x oxide on the surfaces of the TiFe matrix; (2) the Ti4Fe2O1-x cracks; (3) cracks extend into the TiFe matrix; (4) TiFe absorbs hydrogen. Understanding the activation behavior is critical to designing TiFe-based alloys with improved hydrogen storage properties.

Effects of ball milling time on the microstructure and hydrogen storage performances of Ti21.7Y0.3Fe16Mn3Cr alloy

TiFe alloy can store hydrogen at room temperature and low hydrogen pressure, and its theoretical hydrogen storage capacity is up to 1.8 wt%. However, TiFe alloy needs to be activated at high pressure (5 MPa hydrogen) and high temperature (673–723 K), which limits the practical application of TiFe alloy. The as-cast Ti 21.7 Y 0.3 Fe 16 Mn 3 Cr alloy was milled for 0, 0.5, 0.75, 1, and 3 h to study the effects of ball milling on phase structures and hydrogen storage performances. Emphasis was focused on the activation process of as-milled alloys at different temperatures, including the activation process at 483, 443, and 403 K. The results show that the alloys were consisted of TiFe phase, and [Fe, Cr] solid solution. The nanocrystalline boundary produced by milling and the phase boundary provided by the second phase provide a large number of channels for hydrogen diffusion and promote the improvement of hydrogen storage performances. The time required for activation process of as-milled alloys was significantly reduced, and the activation time of as-milled (0.75 h) was only 4 min, and its enthalpy variation for hydrogen absorption and desorption was 22.943 and 26.215 kJ mol −1 H 2 , respectively. • The phase composition and micro-structure of the milled Ti 21.7 Y 0.3 Fe 16 Mn 3 Cr alloy were studied. • Nanocrystalline boundary produced by milling provides many channels for hydrogen diffusion. • Ball milling improves the activation process of the alloy and shortens the activation time. • The optimum milling time of the alloy is 45 min, and its activation time is shortened to 4 min.

Every’s and Blackman’s Diagrams, Cauchy Pressure, and Analysis of Elastic Properties of Crystalline Lattice of Ti49Ni51 (at %) and TiNi–TiFe Alloys with and without Martensitic Transformations

Every’s and Blackman’s Diagrams, Cauchy Pressure, and Analysis of Elastic Properties of Crystalline Lattice of Ti49Ni51 (at %) and TiNi–TiFe Alloys with and without Martensitic Transformations

Re-investigation of high-temperature phase equilibria in Fe-rich Sm–Fe–Ti alloys

Recently renewed attempts to develop high-performance rare-earth-lean permanent magnets based on the Sm(Fe,Ti)12 compound have drawn attention to the limited knowledge about the high-temperature phase equilibria in the Sm–Fe–Ti system. Experimental investigation of equilibrated alloys with electron probe microanalysis, X-ray diffraction and thermomagnetic analysis revealed several inaccuracies in the currently accepted phase relations at 1000 °C and allowed for a revision of the Fe-rich corner of the Sm–Fe–Ti phase diagram. The Sm(Fe,Ti)12 and Sm3(Fe,Ti)29 phases were found to have more extended Ti ranges of 5.1–9.7 at% and 2.8–6.9 at%, respectively. With increasing of the Ti content, the Curie temperature of the Sm(Fe,Ti)12 remains nearly constant at 306–312 °C, whereas that of the Sm3(Fe,Ti)29 increases from 188 °C to 207 °C. The low-titanium Sm3(Fe,Ti)29 phase equilibrates not only with the Sm(Fe,Ti)12 and Sm2(Fe,Ti)17 phases, but also with (α-Fe) solid solution. Newly demonstrated equilibrium between Sm2(Fe,Ti)17 and TiFe2 phases makes impossible the earlier reported equilibrium between the Sm3(Fe,Ti)29 and Sm(Fe,Ti)11 phases. Because of an invariant reaction at 1000 °C, the revised phase diagram also features a class II four-phase equilibrium Sm3(Fe,Ti)29 + TiFe2 + Sm(Fe,Ti)12 + Sm2(Fe,Ti)17. Peritectic decomposition of the Sm(Fe,Ti)11 phase, which occurs either at 1075 °C or at 1087 °C, was found to have among its products the Sm(Fe,Ti)12 phase. Although no such equilibration was attempted, it must be possible to obtain above 1087 °C a two-phase state composed of the Sm(Fe,Ti)12 phase and a liquid – which is important for manufacturing of the Sm(Fe,Ti)12-based permanent magnets via the liquid-phase sintering.

Evaluating some design criteria for TiFe-based ternary hydrogen storage alloys

Elemental substitution is widely practised to fabricate TiFe-based alloys with enhanced hydrogen storage characteristics. While some hydrogen storage properties can be improved others are usually adversely affected by this method. Hence, establishing sensible alloying design criteria is important for further developing Ti-Fe-based alloys. Here, the effects of substitutional elements in Ti-Fe-based ternary alloys are assessed based on several factors such as hydrogen bond dissociation energy, lattice parameters, interstitial site size, and intermetallic phase formation. Our calculations show that all the substitutional elements studied in this work (except Ni and Co) increase the lattice parameter compared to the TiFe alloy, while they have a diverse effect on the interstitial site sizes. The thermodynamic stability of the alloys could not be adequately described based on the lattice parameter and factors such as interstitial site sizes along the local atomic environment should be also considered. Hydrogen storage capacity of the Ti-Fe-based ternary alloys also appears to be influenced by the metal-hydrogen bond dissociation energy of the substitutional elements and their capability to form intermetallic phases with Ti. TiFe-based ternary alloys were modified by V and Zr substitutions according to the above criteria. The modified alloys were mostly composed of the B2 TiFe phase, offering significantly easier activation and a higher reversible hydrogen storage capacity compared to the binary alloy.

A significantly improved hydrogen storage performance of nanocrystalline Ti–Fe–Mn–Pr alloy

Improving the activation performance and increasing the hydrogen storage capacity are the main problems faced by TiFe-based alloys. In this paper, alloys with chemical composition Ti1.1-xPrxFe0.8Mn0.2 (x = 0, 0.02, 0.04, 0.06, 0.08) are designed to achieve a reversible hydrogen storage capacity of 1.81 wt% in 15 min, which is close to the theoretical hydrogen storage capacity of TiFe alloy of 1.86 wt%. Alloys with Pr content x ≥ 0.04 can be directly activated without the incubation period. Transmission electron microscopy analysis found that doping Pr introduced TiFe (111) crystal plane with smaller surface energy, makes it easy for hydrogen atoms to diffuse from the surface to interior. Moreover, the addition of Pr significantly refines the grains and introduces a large number of grain boundaries and defects, improving the activation rate and kinetics. The physisorption results show that the specific surface area of the TiFe-based alloy after hydrogen absorption is significantly increased by doping Pr.

Sintesis dan Karakterisasi Fe₂TiO₅ dari Besi Oksida dan Titanium Dioksida dengan Metode Planetary Ball-Mill

The method of solid hydrogen storage through integration in metal hydride compounds is a new, promising method. This research has succeeded in synthesizing and characterizing the metal hydride alloy Fe-Ti system through a planetary ball-mill process. Based on the XRF analysis, it was found that the composition of Fe oxide content reached 56.22% while Ti oxide reached 43.78%. The FTIR study showed absorption at wavenumbers of 900 cm-1 and 500 cm-1. Both are typical absorptions for Ti-O and Fe-O groups, suggesting that the synthesized sample was successful. It can be seen from the XRD data that some of the diffractogram peaks of the resulting Fe-Ti compound match the peaks of the Fe2TiO5 and TiO2 compounds obtained from the Powder Diffraction File (PDF) database number 00-003-0374. After the refinement was performed, information was obtained that the synthesis of Fe-Ti alloy material using the planetary ball mill technique produced Fe2TiO5.

Effect of oxygen addition on phase composition and activation properties of TiFe alloy

TiFe is one of the most promising hydrogen storage materials owing to its high volumetric hydrogen capacity, moderate operating temperature, and low cost. Oxygen is an inevitable impurity that affects the hydrogen storage properties of TiFe alloys. In this paper, the effect of oxygen addition on the phase composition and hydrogen storage properties of TiFe alloys is systematically investigated. We found that a high oxygen addition improves the initial hydrogen sorption of TiFe. The TiFe-O3.78 alloy achieves full activation after two ab/desorption cycles at room temperature. The high oxygen content facilitates the formation of Ti4Fe2O oxide in TiFe alloy, leading to improved activation kinetics. Moreover, due to the oxygen addition, the amount of TiFe primary phase reduces, and the corresponding hydrogen capacity degrades. Increasing oxygen content also leads to a slight increase in the hydrogenation equilibrium pressure, but almost no impact on the thermodynamics of TiFe alloy.

Developing sustainable FeTi alloys for hydrogen storage by recycling

Intermetallic alloys such as FeTi have attracted ever-growing attention as a safe and efficient hydrogen storage medium. However, the utilization of high-purity metals for the synthesis of such materials poses considerable concerns over the environmental sustainability of their large-scale production. Here, we report an approach for synthesizing FeTi from industrial scraps of iron (steels C45 and 316 L) and titanium (Ti alloy Grade 2) to reduce the carbon footprint associated with FeTi alloy synthesis, without compromising their hydrogen storage properties. At 50 °C and a pressure of 0 to 100 bar, the alloys obtained by using C45-Ti Grade 2 and 316L-Ti Grade 2 can absorb a maximum amount of hydrogen of 1.61 wt.% and 1.50 wt.%, respectively. Moreover, depending on the type of steel utilized, the thermodynamic properties can be modified. Our findings pave a pathway for developing high-performance, environmentally-sustainable FeTi alloys for hydrogen storage purposes using industrial metal wastes.

Hydrogen storage properties of Ti-Fe-Zr-Mn-Nb alloys

TiFe alloy is one of the prime candidates for stationary hydrogen storage applications. However, the practical applications of TiFe alloy are limited by harsh requirements of activation. Alloying is an effective approach for improving the hydrogen storage properties of TiFe alloys. In this paper, we investigate the effect of Nb alloying on the microstructure and hydrogen storage properties of Ti-Fe-Zr-Mn-Nbx (x = 0, 2, 4, 8 at%) alloys. In particular, we found that 2 at% of Nb addition to the alloy enables a good combination of the hydrogen capacity and the activation property, and the Zr-rich phases play a critical role in the activation behavior of Ti-Fe-Zr-Mn-Nbx alloy by absorbing hydrogen before the hydrogenation of the TiFe matrix. However, high Nb addition (>4 at%) leads to the reduction of the Zr-rich phases and thus deteriorates the activation kinetics. Moreover, the Nb addition also favors the formation of the TiFe main phase and promotes higher capacities at ambient temperature. It is also demonstrated that the Nb addition lowers the first plateau pressure and decreases the hysteresis of the isotherms. These correlations between the microstructure and hydrogen storage performance provide insights into tailoring hydrogen storage properties by alloying TiFe with multi-elements.

The Evolution of Surface Oxides during TiFe0.9M0.1 (M = Ni, Mn) Activation: An In Situ XPS Investigation

The nature of TiFe-based surface oxides and their evolution during conventional activation heat treatment were investigated in this study. The as-prepared TiFe alloy was found to possess an initial composite Ti and Fe amorphous surface oxide layer of about 6 nm. Depth profiling has shown that oxides steadily vanish with increasing depth, whereas metallic Fe contribution and mixed Ti oxides arise, before eventually being found in their metallic state at 7.5 nm. In situ XPS measurements, carried out to directly observe the evolution of oxides during the activation procedure, have indicated that the initial ternary oxide begins to transform to metallic Fe and mixed Ti oxides at a temperature as low as 200 °C. Consistent with the literature, the reduction of Ti oxides took a major turn at around 400 °C. Toward the end of the in situ measurements, oxygen was partially dissolved due to the limited measurement duration: TiO and metallic Fe remained beyond 400 °C. A similar overall reduction behavior was observed for the Ni- and Mn-substituted alloys, with a few subtle exceptions: Ni existed in its metallic state from 200 °C whereas Mn was reduced from Mn3+ to the Mn2+ state only beyond 400 °C due to a pronounced difference in the oxidation driving force of these two substitution metals.

Enhanced Supercapacitive Properties of Mixed Oxide Nanotubes Grown by Anodization of Ti–Fe Alloys

Like titanium metal, nanotube array films can be grown on Ti alloys by anodization in fluoride‐containing electrolytes. Further, the anodization of Ti alloys provide a unique pathway to dope TiO2 nanotubes with the alloying element. However, the details of anodization behaviors of Ti alloys and the obtained nanotubes for application in supercapacitors remain poorly understood. Herein, three Ti–Fe alloys containing different amounts of Fe element (10, 15, and 20 wt%) are fabricated by using a vacuum arc melting furnace. Their anodization behaviors are systematically investigated. The nanotube array films can be achieved on these alloys, which are composed of TiO2, Fe2O3, and Fe‐doped TiO2. Their electrochemical behaviors are completely different from both the pure TiO2 and the pure Fe2O3. The mixed oxide nanotubes on Ti–15 wt%Fe have the maximum capacitance among the three Ti–Fe alloys, which is 3.75 times higher than that of pure TiO2. Moreover, the mixed oxide electrode exhibits high rate capability and excellent cycling stability with only 5.7% loss in capacitance over 10 000 cycles. The presented results suggest that the alloy anodization is an efficient strategy for enhancing the performance of TiO2 electrode materials for supercapacitors.

Effects of Zr doping on activation capability and hydrogen storage performances of TiFe-based alloy

Activation difficulty is the key problem limiting the application of TiFe-based hydrogen storage alloys. The addition of transition group elements helps to improve the activation properties of TiFe-based hydrogen storage alloy. In our previous work, the Ti1.08Y0.02Fe0.8Mn0.2 alloy exhibits extremely high hydrogen storage capacity (1.84 wt%) at room temperature with excellent kinetic properties, but it still needs an incubation period of about 1500s. In this study, the composition of Ti1.08Y0.02Fe0.8Mn0.2Zrx (x = 0, 0.02, 0.04, 0.06, 0.08) alloys was prepared by electromagnetic induction melting. The quantitative analysis of elements by energy dispersive spectrometer shows that in the second phase region containing Zr, the content of Ti element is significantly higher than that of Fe. Meanwhile, the first-principle calculation on Zr-doped TiFe system indicates that Zr is more attractive to substitute Ti than Fe. Therefore, the doping of Zr partially replaces the Ti. The solubility of Zr in TiFe is limited, when x ≤ 0.04, the alloy consists of pure TiFe phase. When x > 0.4, the excess Zr forms precipitates, which reduces the reversible hydrogen absorption and desorption capacity of the TiFe alloy. The addition of Zr significantly shortens the activation time and reduces the plateau pressure of TiFe alloys. The Ti1.08Y0.02Fe0.8Mn0.2Zr0.04 alloy can be directly activated without the incubation period and its absolute values of enthalpy change (ΔH) and entropy change (ΔS) are minima (ΔH for 23.2 kJ/mol and ΔS for 83.1 J/mol/K).

A new perspective on the initial hydrogenation of TiFe0.9M0.1 (M = V, Cr, Fe, Co, Ni) alloys gained from surface oxide analyses and nucleation energetics

Despite the promise of TiFe-based alloys as low-cost solid-state hydrogen storage materials with mild operating conditions and reasonable hydrogen capacity, their initial hydrogenation process is difficult, hindering broad utilization. The effect of alloying element on the initial hydrogenation kinetics of TiFe alloys, TiFe0.9M0.1 (M = V, Cr, Fe, Co and Ni), was evaluated by analyzing changes to the passivating surface oxide layer that inhibits hydrogen permeation, as well as the ease of initial-stage hydrogen absorption into the underlying matrix. X-ray photoelectron spectroscopy and atom probe tomography revealed key variations in surface oxide compositions and thinning of the passivating oxide layer compared to pure TiFe, which suggests suppressed oxide growth by alloying-induced elemental redistribution. At the same time, density functional theory calculations predicted exothermic formation of hydride nuclei when alloying with V or Cr, as well as a reduced nucleation barrier when alloying with Co or Ni. Overall, these results are consistent with the observed experimental trend of the activation kinetics. We propose that improvements in activation kinetics of TiFe with alloying arises from the combined effect of reduced passivating oxide thickness and easier hydride nucleation, offering a starting point for alloy design strategies towards further improvement.

Effect of yttrium content on microstructure and hydrogen storage properties of TiFe-based alloy

In this paper, the experimental alloy with the standard composition of Ti1.1-xZr0.1YxFe0.6Ni0.3Mn0.2 (x = 0–0.08) was synthesized by vacuum induction melting. The activation properties and hydrogen absorption/desorption kinetics were significantly improved by adding different amounts levels of rare earth elements Y to partially replace Ti in TiFe alloys. The microstructure, phase composition and hydrogen storage properties of the alloy before and after hydrogen absorption/desorption were characterized and tested by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Sieverts-type manual PCT hydrogen storage tester. The experimental results show that the as-cast alloy consists of Ni-rich TiFe main phase, a small amount of ZrMn2 phase biased on the TiFe phase and Y-rich phase. The addition of Y significantly increases the phase boundary and refines the crystallization, and significantly shortens the activation incubation period of the cast alloy. The alloy requires only the first hydrogen absorption to fully achieve activation at 150 °C, and still exhibits a fast hydrogen absorption rate at −10 °C. Meanwhile, When the Y content is 0.02, the saturation rate (R100a) of hydrogen absorption reaches 92%, and the maximum hydrogen absorption capacity is 1.704 wt% at 70 °C. And the absolute values of the enthalpy and entropy changes of hydrogen absorption/desorption increase with the increasing of Y content.

Effect of oxygen on the hydrogen storage properties of TiFe alloys

Hydrogen storage is one of the critical barriers to the hydrogen-based clean energy supply chain. TiFe alloy is a prime candidate material for stationary hydrogen storage, which can play a critical role in the deployment of variable renewable energies. However, the understanding of the hydrogen storage properties of TiFe alloy and the development of industrially deployable storage technologies based on TiFe are still in their nascent stage. The properties of TiFe alloy rely strongly on the presence of oxygen due to the strong affinity of Ti to oxygen. This work systematically investigated the effects of oxygen on the equilibrium pressure of TiFe-H intermetallic hydride. We aim to understand how the oxygen content affects the (de)hydrogenation behavior of TiFe alloys. Specifically, we found that the oxygen can dissolve in the TiFe phase and form solid solutions of TiFe-O. During the thermochemical synthesis process of TiFe, with the increase of annealing time, the Ti4Fe2O phase decreases, and the oxygen in TiFe increases. The increase of oxygen content in the TiFe results in the increase of equilibrium pressure of the TiFe alloy. It suggests that the oxygen dissolved in TiFe can destabilize the TiFe-H hydride and alter the thermodynamics of the TiFe-H system.

Hydrogen storage characteristics of Ti1.04Fe0.7Ni0.1Zr0.1Mn0.1Pr0.06 alloy treated by ball milling

In order to enhance the hydrogen storage performances of TiFe alloy, the Ti1.04Fe0.7Ni0.1Zr0.1Mn0.1Pr0.06 alloy was prepared through using transition metals (Ni, Mn, Zr) partially substitute Fe and rare earth Pr partially substitute Ti. The microstructure of the alloy was further adjusted by ball milling for different time. The master alloy contained TiFe, Ti2Fe and Pr phases. Ball milling treatment led to the reduction of the particle size and grain size. The master alloy (M-0 sample) and the alloys with short-time ball milling treatment (M-0.5 and M-1 samples) absorbed hydrogen immediately at the first hydrogenation cycle at 423 K and 3 MPa H2, while the alloys with long-time ball milling treatment (M-3 and M-5 samples) showed an incubation time. The M-0.5 sample not only presented the optimum activation property, but also showed the most outstanding hydriding/dehydriding kinetics and capacity. It achieved the saturated hydrogenation state within 2158 s. The hydrogenation capacity was 1.471, 1.626, 1.547, 1.485 and 1.417 wt% for the M-0, M-0.5, M-1, M-3 and M-5 samples at 313 K and 3 MPa H2, respectively. In addition, ball milling treatment caused the decrease of cell volume of TiFe phase in the samples, which reduced the thermodynamic stability of the hydrides.

Magnetic Properties and Microstructures of Sm–Fe–Ti Alloys With ThMn12 Structure Prepared by Melt-Spinning Method

The effects of annealing temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{a}$ </tex-math></inline-formula> , 600 °C–950 °C) and Sm content on the phase transformation and magnetic properties of Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> Ti ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x $ </tex-math></inline-formula> = 0.9, 1.0, and 1.1) alloys prepared by the melt-spinning method were investigated. In all specimens with different compositions, the crystal structure was transformed from the TbCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> to ThMn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> structure as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{a}$ </tex-math></inline-formula> increased. The coercivity reached 6.3 kOe in a SmFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> Ti ribbon annealed at 850 °C. However, the grain size of this ribbon was much smaller than the critical single domain size of the SmFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> Ti alloy. The microstructural analysis revealed that the ribbons were highly strained. To overcome the abnormal low coercivity of SmFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> Ti alloy, precise control of the composition and removal of strain without grain growth are the critical factors.

Phase decomposition upon heat-treatment of a eutectoid Ti-Fe alloy processed by dual-wire-arc additive manufacturing

Titanium alloys are among the most relevant structural materials for aerospace applications; they can be processed using various additive manufacturing (AM) techniques including wire-based AM. However, conventional alloy systems, such as Ti-6Al-4V, are, from a metallurgical perspective, not optimized for AM. Here, we investigate the effects of alloying Ti with Fe using dual-WAAM to improve the understanding of the effects of the addition of β-eutectoid forming elements on the microstructure. A structural characterization of the material after processing reveals the microstructure in the as-built condition to primarily consist of β-phase from which α-phase is precipitated upon a heat-treatment, resulting in a substantial increase in hardness.