Fe-Ti Alloys Research Articles

Phase transformation and mechanical properties of nanocrystalline Ti–2Fe-0.1B alloy processed by high pressure torsion

In this paper, nano-Ti-2Fe-0.1B alloys with different grain sizes were processed by high pressure torsion (HPT) deformation. The study examined the microstructural evolution of the Ti–2Fe-0.1B alloy during HPT and evaluated its mechanical properties through microhardness and tensile tests. The results of the microstructural observations revealed that the grain size of the Ti–2Fe-0.1B alloy progressively decreased from 3.14 μm in the as-annealed state to approximately 20 nm after 10 turns. In the initial state, the alloy consists of α-phase and β-phases, with a volume ratio of approximately 5:1. During the HPT process, transformations of α-phase and β-phase to ω-phase were observed. The primary reason for this is that the shear forces applied during the HPT process facilitated the phase transformation of the α-phase. Additionally, the presence of Fe element in the alloy altered the lattice compatibility between the grains of β-phase and ω-phase, thereby promoting the phase transformation of the β-phase, with the accumulated turns of HPT process, the fraction of ω-phase increased in the beginning gradually, then decreased, which reached to the maximum 80.8% in the 5 turns. This is higher than that of pure titanium and Ti–Fe alloys under the same conditions, because the proportion of the ω-phase increases with the increase in Fe content. Studies of mechanical properties demonstrated that HPT can substantially enhance the hardness of Ti–2Fe-0.1B alloys to as high as 483 HV, and the tensile strength of the Ti–2Fe-0.1B alloy was observed to increase from 725 MPa to 1568 MPa after 5 turns, which is much higher than Ti–6Al–4V subjected to the identical processing conditions. It can be ascribed to the exist of mass ω-phase as well as finer grain size in nanocrystalline Ti–2Fe-0.1B alloy.

Solidification and microstructure investigation on as-cast and annealed hypoeutectic Ti–Fe alloys

This work explored the solidification behavior, microstructure development, and resulting mechanical properties of hypoeutectic Ti–Fe alloys under both as-cast and annealed conditions. Ti-(27, 28, 29)Fe (wt%) alloys were synthesized through arc-melting, followed by annealing at 950 °C for 24 h and slow furnace cooling. The investigation procedures included thermodynamic calculations, differential scanning calorimetry, scanning electron microscopy, high-temperature laser-scanning confocal microscopy, X-ray diffraction, hardness measurements, and compression tests. The study demonstrated the efficacy of annealing treatments in reducing excess eutectic in the as-cast structure formed during solidification. Results from both thermodynamic calculation and experiment for the solidification process demonstrated reasonable agreement. The high β-stabilizing effect of Fe ensured the presence of the β phase at room temperature under both studied conditions. The solid-solution hardening of the β phase, coupled with the TiFe intermetallic, substantially contributed to the increased hardness and mechanical strength, although the increase in brittleness was noticeable in the as-cast state. Subsequent annealing enhanced plasticity but resulted in a reduction in strength, albeit maintaining yield strength at a considerable level, approximately 1450 MPa.

Effect of alloying on the cleanliness of Ti-stabilised interstitial-free (IF) steel during Ruhrstahl–Heraeus (RH) treatment

To understand the alloying process on the cleanliness of Ti-stabilised interstitial-free (IF) steel, two different alloying operation processes were conducted during Ruhrstahl–Heraeus (RH) treatment. It was found that the Ti–Fe alloy contains extremely high oxygen and nitrogen contents. After Al addition, [Al]–[O] deoxidation reaction can quickly get close to equilibrium (within 1 min), and most inclusions are pure Al2O3. After Ti–Fe addition, the TiO x content in the inclusions increases first and then drops. Because the average content of TiO x is lower than 10 mass%, most inclusions should be solid. The addition of Ti–Fe alloy just after Al addition would not evidently weaken the yield of Ti–Fe alloy, or influence the removal efficiency of the inclusions. Due to the longer RH circulation time after Ti–Fe addition, the inclusions and impurities in the alloy can be further removed, resulting in better steel cleanliness.

Unveiling the correlation between anomalous hardening and grain boundary diffusional transformation in ω single-phase nano-grained Ti-Fe alloy

A metastable ω single-phase nanograined (NG) Ti-Fe alloy was synthesized using laser inert-gas condensation (IGC). Upon being annealed at 360 °C, the NG Ti-Fe alloy exhibited a remarkable ultra-hardening, increasing the hardness from 4.7 to 8.6 GPa. Subsequent findings revealed an unexpected hardness enhancement, rising from 6.6 GPa at 420 °C to 7.6 GPa at 460 °C, despite the occurrence of grain growth. In-depth investigations into the strengthening mechanisms of the NG Ti-Fe alloy were conducted using in-situ synchrotron high-energy X-ray diffraction (XRD) and transmission electron microscopy (TEM). The comprehensive analysis unveiled that the diffusion-controlled structure evolution during annealing played a pivotal role in enhancing the alloy’s mechanical properties. This study not only presents the synthesis of a novel metastable alloy but also provides valuable insights into the intricate relationship between diffusion-controlled structure evolution and the resulting superior mechanical properties.

Synergetic Effect of FeTi in Enhancing the Hydrogen-Storage Kinetics of Nanocrystalline MgH2

High-energy ball milling was applied to produce nanocrystalline MgH2-FeTi powder composites. In order to achieve a remarkable synergetic effect between the two materials, the amount of the FeTi catalyst was chosen to be 40 wt.%, 50 wt.% and 60 wt.%. The morphology and microstructure of the as-milled powders were characterized by scanning electron microscopy and X-ray diffraction, respectively. The evaluation of the diffraction profiles by the Convolutional Multiple Whole Profile fitting algorithm provided a detailed microstructural characterization of the coherently scattering α-MgH2 crystallites. Differential scanning calorimetry experiments revealed two overlapping endotherms corresponding to the dehydrogenation of metastable γ-MgH2 and stable α-MgH2 hydrides. Isothermal hydrogen-sorption experiments were carried out in a Sieverts-type apparatus. It was established that the MgH2-40 wt.% FeTi powder is capable of absorbing 5.8 wt.% hydrogen, while extraordinary absorption kinetics were observed for the MgH2-50 wt.% FeTi alloy, i.e., 3.3 wt.% H2 is absorbed after 100 s.

Thermodynamics of Aluminothermic Processes for Ferrotitanium Alloy Production from Bauxite Residue and Ilmenite

Titanium oxide is a major component of bauxite residue (BR) with a high value, but it is often an unwanted element in common BR reuse options such as cement or iron production. Conventional carbothermic reduction smelting of BR produces a slag still containing a large amount of Ti. This study investigates an aluminothermic process for producing an FeTi alloy by combining BR, ilmenite ore, and fluxes. Based on thermodynamic calculations and batch experiments, the amounts of aluminum (reductant) and fluxes were investigated to achieve the optimum alloy production in parallel with a slag that could be further valorized in the cement industry. The mineralogical and chemical analysis of the metallic and slag phase agreed with the thermodynamic calculations. The results obtained by this study can lead to the development of a new process for the complete valorization of BR, paving the way for scaling up aluminothermic processes for producing ferroalloys from all iron-rich residues.

Heat treatment effects on microstructure and properties of Cu–Ti–Fe alloys

High-strength Cu–Ti–Fe alloys were prepared and investigated in this study. The alloy was subjected to cold deformation and aging treatment, and revealed the transformation mechanism of the microstructure and properties. Cold deformation of 60 %, aging at 450 °C for 240 min, can optimize the hardness and conductivity of the Cu–Ti–Fe alloy. The hardness and electrical conductivity of Cu-1.5Ti-0.3Fe alloy increased from 196.8 HV to 7.8 % IACS to 269.3 HV and 19.8 % IACS after aged. Cu4Ti and Fe2Ti are the mainly precipitated phases in Cu–Ti–Fe alloy, which effectively obstructs dislocations slipping and delays recrystallization, and the most important strengthening mechanism. The concentration of solute atoms increased could further improve the grain boundary strengthening, solution strengthening, and deformation strengthening.

Effect of Al-Ti complex deoxidation mode on steel cleanliness during RH refining of IF steels

The deoxidation in Ti containing Al killed IF steels is a vital parameter that directly influences the steel cleanliness. In this study, the evolution of steel compositions and inclusion characteristics during RH refining of IF steels were investigated by industrial trials involving three Al-Ti deoxidation modes, which were adding Ti-Fe 2 min after Al deoxidation in Mode I, adding Al and Ti-Fe simultaneously in Mode II, and adding Ti alloys with two equal batches at 3.2 min and 5 min after Al deoxidation in Mode III. The results showed that nitrogen pickup of several ppm was observed with Ti-Fe alloy addition. Therefore, nitrogen content in alloys should be strictly controlled. The main inclusions were single alumina particles, alumina clusters, alumina cluster with Al-Ti oxides, and Al-Ti complex oxides. Mode III had less amount of Al-Ti oxides compared with Mode I, and Mode II had a much higher proportion of Ti bearing inclusions than Mode I and Mode III at RH end. For Mode I & Mode III, the inclusion removal rate was 0.33–0.35 min−1 before adding Ti, and slowed down to 0.14 min−1 for Mode I and 0.22 min−1 for Mode III after Ti-Fe addition. While for Mode II, the rate was only 0.18 min−1. Mode III was the recommended mode for its excellent steel cleanliness and high Ti yield with slight elongation of RH treating time.

Improved hydrogen storage kinetics of MgH2 using TiFe0.92Mn0.04Co0.04 with in-situ generated α-Fe as catalyst

While TiFe alloy has recently attracted attention as the efficient catalyst to enhance de/hydrogenation rates of Mg/MgH2, the difficulty of its activation characteristics has hindered further improvement of reaction kinetics. Herein, we report that the TiFe0.92Mn0.04Co0.04 catalyst can overcome the abovementioned challenges. The synthesized MgH2-30 wt% TiFe0.92Mn0.04Co0.04 can release 4.5 wt% of hydrogen in 16 min at 250 °C, three times as fast as MgH2. The activation energy of dehydrogenation was as low as 84.6 kJ mol−1, which is 46.8% reduced from pure MgH2. No clear degradation of reaction rates and hydrogen storage capacity was observed for at least 30 cycles. Structural studies reveal that TiFe0.92Mn0.04Co0.04 partially decomposes to in-situ generated α-Fe particles dispersed on TiFe0.92Mn0.04Co0.04. The presence of α-Fe reduces the formation of an oxide layer on TiFe0.92Mn0.04Co0.04, enabling the activation processes. At the same time, the hydrogen incorporation capabilities of TiFe0.92Mn0.04Co0.04 can provide more hydrogen diffusion paths, which promote hydrogen dissociation and diffusion. These discoveries demonstrate the advanced nature and importance of combining the in-situ generated α-Fe with TiFe0.92Mn0.04Co0.04. It provides a new strategy for designing highly efficient and stable catalysts for Mg-based hydrogen storage materials.

Influence of the Phase Composition of Titanium Alloys on Cell Adhesion and Surface Colonization.

The pivotal role of metal implants within the host's body following reconstructive surgery hinges primarily on the initial phase of the process: the adhesion of host cells to the implant's surface and the subsequent colonization by these cells. Notably, titanium alloys represent a significant class of materials used for crafting metal implants. This study, however, marks the first investigation into how the phase composition of titanium alloys, encompassing the volume fractions of the α, β, and ω phases, influences cell adhesion to the implant's surface. Moreover, the research delves into the examination of induced hemolysis and cytotoxicity. To manipulate the phase composition of titanium alloys, various parameters were altered, including the chemical composition of titanium alloys with iron and niobium, annealing temperature, and high-pressure torsion parameters. By systematically adjusting these experimental parameters, we were able to discern the distinct impact of phase composition. As a result, the study unveiled that the colonization of the surfaces of the examined Ti-Nb and Ti-Fe alloys by human multipotent mesenchymal stromal cells exhibits an upward trend with the increasing proportion of the ω phase, concurrently accompanied by a decrease in the α and β phases. These findings signify a new avenue for advancing Ti-based alloys for both permanent implants and temporary fixtures, capitalizing on the ability to regulate the volume fractions of the α, β, and ω phases. Furthermore, the promising characteristics of the ω phase suggest the potential emergence of a third generation of biocompatible Ti alloys, the ω-based materials, following the first-generation α-Ti alloys and second-generation β alloys.

An overview of TiFe alloys for hydrogen storage: Structure, processes, properties, and applications

Hydrogen-based energy systems offer potential solutions for replacing fossil fuels in the future. However, the practical utilization of hydrogen energy depends partly on safe and efficient hydrogen storage techniques. The development of hydrogen storage materials has attracted extensive interest for decades. Solid-state hydrogen storage systems based on metal hydride materials provide great promises for many applications. Recently, interest has been revived in TiFe alloys as a prime candidate for stationary hydrogen storage material. The advantages of TiFe alloys over some of the other solid metal hydrides include that it can hydrogenate and dehydrogenate at near room temperature under near atmospheric pressures and that it is a low-cost material because there are abundant supplies of Fe and Ti on the earth's crust. However, the TiFe alloy must be activated at relatively high temperatures (400–450 °C) and high pressure of hydrogen (65 bar) before it can be hydrogenated, which is a hindrance to the industrial-scale application of TiFe alloys. The materials science community on hydrogen storage materials has conducted and reported considerable amounts of studies on TiFe-based alloys. In this work, we provided a comprehensive review of TiFe-based alloys. The fundamentals and synthesis approaches of TiFe-based alloys were summarized. The activation properties of TiFe-based alloys including the understanding of the activation mechanisms and the methods for improving the activation kinetics were reviewed. Moreover, the cycle stability and anti-poisoning ability were discussed. Finally, the potential applications and the perspective of TiFe-based alloys were introduced.

Theoretical Predictions of Structure, Mechanics, Dislocation, and Electronics Properties of FeTi Alloy at High Pressure

The influences of applied pressure on the structure, mechanics, dislocation, and electronics properties of an FeTi hydrogen storage alloy are theoretically investigated via first-principles calculations. The lattice parameter ratio, elastic constant, Young’s modulus, bulk modulus, shear modulus, ductile/brittle, Poisson’s ratio, anisotropy, Cauchy pressure, yield strength, Vickers hardness and energy factor are discussed versus applied pressure. The results show that the FeTi alloy exhibits good mechanical stability under applied pressure between 0 and 50 GPa, and the mechanical properties are significantly improved under applied pressure, like the resistances to elastic, bulk, and shear deformations, the material ductility and metallicity, as well as Vickers hardness and yield strength. Moreover, the electronic structures reveal that the FeTi alloy has metallic properties and the structural stability of the FeTi hydrogen storage alloy is enhanced at high pressure. This work provides significant value for high-pressure applications of FeTi alloys in hydrogen storage and supply fields.

On the hydrogen storage properties of cast TiFe mechanically milled with an intermetallic LaNi5 and rare-earth elements La and Ce

This study provides detailed insight into the effects of adding an intermetallic LaNi5 and rare earth elements La and Ce on the hydrogen storage properties of cast TiFe alloy. To preserve the composite nature of the materials, the addition was done by short-duration ball milling. Morphological investigation revealed the presence of two distinct regions, viz., the primary matrix TiFe region and a secondary region mainly containing the additives. The relative abundance of La and Ni were close to 1/5 in both the regions indicating that LaNi5 did not decompose, and no La–Ni–Ti–Fe phase formed. In the La-added TiFe, diffraction peaks correspond to a high-temperature La phase, and in the Ce-added TiFe, peaks indicative of CeO2 rather than elemental Ce were observed. The milling process only induced microstrains in the LaNi5-added TiFe. Notably, hydrogenation was more complete and faster when the additive was Ce and completely reversible when the additive was LaNi5. However, the kinetics of the La-added TiFe were slow, and stable LaH3 was observed.

Influence of β-Stabilizer Element on Microstructure and Mechanical Behavior of Porous Titanium Alloy Synthesized by Liquid Metal Dealloying.

The metallic implant materials for load-bearing applications typically possess a significantly higher stiffness when compared with that of human bone. In some cases, this stiffness mismatch leads to a stress-shielding effect and eventual loosing of the implant. Porous metallic materials are suitable candidates to overcome this problem. In this study, we synthesized low modulus open porous TiFe alloy by liquid metal dealloying of the precursor Ti47.5Fe2.5Cu50 (at.%) material in liquid Mg. Upon liquid metal dealloying, Cu was selectively dissolved from the precursor, and the remaining Ti and Fe elements were reorganized into a bicontinous porous structure. The synthesized TiFe alloy is composed of α-titanium and β-titanium phases. The average measured ligament size is in the micrometer range. It was found that a higher dealloying temperature leads to a pronounced coarsening of the microstructure. The open porous TiFe alloy possesses a low elastic modulus of about 6.4-6.9 GPa. At the same time, its yield strength value reaches about 185 MPa due to the α + β microstructure. Its attractive mechanical properties for biomedical applications, together with its open porous structure, indicate the potential of porous TiFe alloys to be used as implants.

Optimizing strength and electrical conductivity of Cu–Fe–Ti alloy by pre-aging treatment

Pre-aging treatment before cold rolling and final aging was introduced to optimize the mechanical properties and electrical conductivity properties of Cu-0.75Fe-0.35Ti alloy. The alloy was pre-aged at 540 °C for 6 h, then cold rolled with thickness reduction of 80%, followed by aging at 460 °C for 2 h (SARA). Vickers hardness, electronic conductivity and uniaxial tensile tests were conducted to measure the mechanical and electrical conductivity properties. Electron backscatter diffraction and transmission electron microscope were used to characterize the microstructural evolution. The results showed that the hardness, tensile strength and electrical conductivity of SARA were up to 198.2 ± 4.8 HV, 622.6 ± 6.3 MPa and 63.8% IACS, respectively, which were superior to those achieved without pre-aging. The enhanced mechanical properties of SARA were attributed to an increase in low angle boundaries (LABs), geometrically necessary dislocation (GND) density and volume fraction of precipitates, while the favorable electrical conductivity was ascribed to the enhancement of precipitation and resultant matrix purification.

Physicochemical and Service Properties of Nb–Si–Al–Fe–Ti Alloys

Physicochemical and Service Properties of Nb–Si–Al–Fe–Ti Alloys

Application of Pettifor and Pugh Criteria in Analysis of Plasticity and Brittleness of TiNi–TiFe Alloys with and without Shape Memory Effect

Application of Pettifor and Pugh Criteria in Analysis of Plasticity and Brittleness of TiNi–TiFe Alloys with and without Shape Memory Effect

Effect of addition of rare earth element La on the hydrogen storage properties of TiFe alloy synthesized by mechanical alloying

In this paper, we report the effect of adding the rare earth element lanthanum on the hydrogen storage properties of TiFe synthesized by mechanical alloying (MA). A remarkable improvement was observed in the first hydrogenation (activation) of La-added TiFe. Milling led to the refinement of the crystallite size of the TiFe alloy leading to nanocrystallinity. The formation of a stable hydride phase LaH3 facilitated heterogeneous nucleation and acted as a gateway for the hydrogenation of the TiFe phase. No change in thermodynamics was observed for the rare earth-added TiFe compared to pure TiFe reported in the literature. The microstructure revealed a uniform distribution of the elements. However, La was completely immiscible with the TiFe alloy-a conclusion drawn from the thermodynamics study of the sample. Also investigated was pure TiFe synthesized by MA and arc melting to compare these two synthesis methods.

Intrinsic mechanisms of superior hydrogen storage properties in V–Fe–Ti alloys: A combined experimental and theoretical study

Vanadium-based alloys have excellent reversible hydrogen storage properties, and the empirical lattice parameter law is often used experimentally for optimization of alloy composition. To reveal the underlying mechanisms, hydrogen storage properties and local environmental effect of H dissolution in V–Fe–Ti alloys were studied experimentally and computationally. The experimental results show that adding Fe and Ti has opposite effects on the hydrogen storage capacity of alloys, and (V85Fe15)100-xTix alloys with 20%Ti addition can exhibit the best performance, which satisfies the empirical lattice parameter law. Furthermore, atomic-scale simulations have demonstrated that H dissolution is affected by its dissolution location and surrounding alloy species through comparing the stability, electronic structure, and bonding characteristics of different V-based alloys. Besides, the correlation analyses of different factors with the hydrogen dissolution energy verify the rationality of the empirical law. Our findings provide useful insight into the rational design of Fe–V–Ti alloys for high-capacity hydrogen storage.

Powder metallurgy metastable Ti alloys via lean Fe and Mn additions

The addition of Fe and Mn to Ti has previously been considered in binary Ti-Fe and Ti-Mn alloys. However, their combined addition has not been properly exploited. In this study, simultaneous lean additions of Fe and Mn were used to create new metastable Ti alloys to be processed via powder metallurgy. It was found that lean additions of Fe and Mn result in the sintered metastable Ti alloys having a lamellar structure. Such microstructure is composed of colonies with comparable size and finer α+β lamellae as the amount of Mn and Fe increases. Furthermore, Mn is a stronger β stabiliser than Fe, and leads to finer microstructures. The addition of the Fe and Mn powder particles lowers the compressibility but increases the densification due to high diffusivity of these elements. Consequently, the amount of residual porosity decreases (8.2 → 7.2%) for higher additions of Fe and Mn. Moreover, the sintered metastable Ti alloys become less ductile but stronger (YS: 608–702 MPa for YS and 678–739 MPa for UTS) as the amount of alloying elements increases. Dimples generated from residual pores and fracture at the colonies/α+β lamellae boundaries comprise the fracture surface of the sintered metastable Ti alloys. The alloys fail in an intergranularly ductile manner.