TiAl Research Articles

Electromagnetic characterization of MAX phase and MXene in Ti–Al–C ternary system

The present paper set out to investigate the synthesis and electromagnetic characterization of Ti3AlC2 MAX phase and Ti3C2Tx MXene in Ti–Al–C ternary system. In this regard, Ti3AlC2 MAX phase was synthesized using mechanical milling process of TiC, Al, and Ti powder mixtures based on 2TiC–Al–Ti + xAl (x = 0, 0.25, 0.5, 0.75 and 1). The HF acidic etching was also employed to synthesize the Ti3C2Tx MXene. Structural and electromagnetic characterizations of the prepared samples were conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vector network analyzer. The obtained results point to the impossibility of the formation of Ti3AlC2 single-phase structure in stoichiometric system. In other word, development of the Ti3AlC2 single-phase structure is only possible in non-stoichiometric 2TiC–2Al–Ti system. The minimum reflection losses of the prepared Ti3AlC2 MAX phase was estimated to be around −30.73 dB at the matching frequency of 15.25 GHz. The results further revealed that the etching time affects electromagnetic behavior of the MXene. That is, an increase in the etching time brings about a change in the reflection loss (RL) from −24.17 to −5.69 dB within the frequency range of 1–18 GHz.

Microstructure and mechanical properties of non-heat-treated Al–8Si-0.2Mg-0.5Mn alloy inoculated by Al–Nb–B refiner

Al–Nb–B refiner has been considered as an alternative to Al–Ti–B refiner for hypoeutectic Al–Si alloys due to Si-poisoning effect. In this paper, the effects of Al–Nb–B and Al–Ti–B refiner on the microstructure and mechanical properties in indirect squeeze casting Al–8Si-0.2Mg-0.5Mn alloy were compared. Results show that the grain sizes in the edge chilling layer, segregation band, and the center region of the Al–Nb–B refined alloys were refined by 13.9%, 12.5%, and 17.6% compared to Al–Ti–B refined alloys, respectively. The yield strength, tensile strength, and elongation of Al–Nb–B inoculated alloys were superior to those of the unrefined alloys and Al–Ti–B inoculated alloys. The coexistence of NbAl3 and NbB2 particles in the Al–Nb–B refiner exhibited excellent anti Si-poisoning capability. They significantly decreased the grain size and uniformly distributed the eutectic Si particles and Fe-rich phases, resulting in an increase in the yield strength of the alloy by 16.1% compared to the Al–Ti–B inoculated alloy. The distribution of iron-rich phases in the segregation band was affected by the inoculation. The size of α-Al15(Fe, Mn)3Si2 phase in Al–Ti–B inoculated alloys was refined, and the number significantly increased, resulting in a decrease in tensile strength of 12.82 MPa. In the Al–Nb–B inoculated alloys, the size and number of α-Al15(Fe, Mn)3Si2 phase decreased, and the δ-Al4FeSi2 phase increased, which effectively improved the fracture toughness and ductility. In addition, with the increase in grain refinement (from unrefined to Al–Ti–B to Al–Nb–B inoculated alloy), the fracture behavior changed from trans-granular fracture to intergranular fracture, improving the fracture toughness.

Influences of the composition design on the microstructure and properties of laser additive manufacturing TiAl alloy coatings

The utilization of titanium aluminide (TiAl) alloys is widespread in the high-temperature sectors of the aerospace industry, despite their challenging manufacturing process and inherent low toughness. Laser additive manufacturing (LAM), as a solution to these challenges, enhances the capability to form complex components and mechanical properties. The influence of process parameters, heat treatment methods, and reinforcing components on the microstructure of TiAl alloys was studied during the LAM process. The principles of designing TiAl alloys were emphasized from the action mechanism of reinforcing components. A classification standard for the component design was proposed based on the different roles of β-stabilizing elements, α-stabilizing elements, rare earth elements, and composites (a combination of the aforementioned components). Furthermore, the work discussed the evolution mechanism of the microstructure and the strengthening mechanism of mechanical properties in TiAl alloys prepared using LAM. These included solid solution strengthening, precipitation strengthening, grain boundary strengthening, grain refinement, and lattice distortion toughening. Finally, future research directions in LAM TiAl alloys were proposed—the innovative design of TiAl alloys through the structural or interfacial control, the development of multiscale characterization techniques for microstructures, and the advancement of high-performance TiAl alloys using data-driven machine learning approaches.

The effect of nitrogen on the tensile strength of Ti–22Al–25Nb alloy using laser beam powder bed fusion

Titanium-aluminum (TiAl) based alloys have a wide application prospect in aerospace and auto-industry fields due to low density, good physical and mechanical performances. However, the mechanical strength of TiAl-based alloys is also put forward more stringent requirements with the complexity of the application conditions. In this work, an argon-nitrogen (Ar–N2) reactive atmosphere was designed to achieve nitrogen interstitial solid-solution strengthening of Ti–22Al–25Nb alloy during the laser beam powder bed fusion (PBF-LB) process. An in-depth microstructure and mechanical performance analysis for the as-printed sample under various atmosphere conditions were performed via scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The nitrogen atoms can be dissolved in the octahedral gap of the β phase through the PBF-LB in the Ar–N2 atmosphere, and a small amount of nitride was detected when the volume ratio of Ar to N2 was 95:5. Compared with 100 vol% Ar atmosphere condition, finer grains of the β phase can be obtained after using the mixed gas atmosphere, and the ratio of the O phase was significantly reduced. The yield strength and ultimate tensile strength can be increased from 932 MPa to 947 MPa–1080 MPa and 1099 MPa at room temperature, respectively. At the same time, the elongation reaches ∼11 % while obtaining higher tensile strength. The strength of as-printed Ti–22Al–25Nb alloy was improved by adopting a practical methodology without sacrificing plasticity.

Preparation and Characterization of Ti‐6‐4 and Ti‐8‐1‐1 Metal Matrix Composites with High Specific Stiffness Using Powder Hot Extrusion and Arc Remelting

Titanium alloys with high stiffness are crucial for aerospace engineering and are often fabricated using additive manufacturing (AM) methods like arc or laser techniques. These high energy processes alter the microstructure and mechanical properties. To enhance stiffness, TiC and B4C are added to Ti–6Al–4V and Ti–8Al–1Mo–1V alloys via powder hot extrusion. The resulting metal matrix composites (MMCs) are analyzed in both their as‐extruded and heat‐treated states for microstructure and mechanical properties. To simulate an AM process, samples are remelted using a gas tungsten arc‐welding (GTAW) torch and examined. In the results, it is shown that TiC and B4C increased mechanical properties up to 2 GPa cm3 g−1, with the highest increase observed in heat‐treated B4C samples, achieving specific stiffnesses of 34.6 GPa cm3 g−1 (Ti–6Al–4V) and 32.3 GPa cm3 g−1 (Ti–8Al–1Mo–1V). Powder hot extrusion proves effective in producing Ti–MMCs with high stiffness even with reactive ceramic additions. However, GTAW remelting leads to the decomposition of TiC‐reinforced Ti–MMCs, significantly altering morphology and reducing stiffness below that of the base alloy.

Microstructural characterization of recycled Al–Mg–Si-based alloys upon the synergistic effect of ultrasonic technology (UT) and novel refiners

Ultrasound, as an efficient, clean, and safe processing technology, is widely used in industries. Grain refiners are widely used in the refinement of cast alloys. In this study, ultrasonic technology (UT) and Al–5Ti–1B refiner prepared by continuous rheological extrusion (CRE Al–5Ti–1B) were used to modify the recycled Al–Mg–Si-based alloy, and the microstructure and mechanical properties of the recycled Al–Mg–Si-based alloy were studied. The differences in porosity and grain refinement caused by ultrasonic power were discussed. Results showed that, increasing the ultrasonic power can effectively reduce the porosity of the recycled Al–Mg–Si-based alloy. The synergistic effect of UT and CRE Al–5Ti–1B refiner significantly refined α-Al grains and second phases. The increase of ultrasonic power can effectively cause deagglomeration while reducing the nucleation undercooling of α-Al, which promotes the refinement of the recycled Al–Mg–Si-based alloy and significantly improves the mechanical properties. The yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of the recycled Al–Mg–Si-based alloy were 106 MPa, 210 MPa and 9.4%, respectively. When 0.2 wt% CRE Al–5Ti–1B refiner was added and the ultrasonic power was 150 W, the YS, UTS, and EL were improved by 12.8%, 28.8% and 228.4%, respectively.

Microstructure evolution and nano-precipitate of multi-stage heat-treated Ti–45Al–2Nb–2Cr-0.3C alloy

This work thoroughly examined the microstructure evolutions of the cast Ti–45Al–2Nb–2Cr-0.3C alloy after multi-stage heat treatments, involving solid solution, cyclic quenching and isothermal annealing. The experimental findings revealed that solid solution and isothermal annealing processes decreased the lattice constants of component parameters, while the cyclic quenching resulted in the lattice expansion. The blocky (B2+γ) phases, which had been distributed along the colony boundary of the as-cast microstructure, disappeared after multi-stage heat treatment, and the lamellae showed a trend of thinning first and then thickening. In addition, the cyclic quenching process resulted in a large number of dislocations and stacking faults within γ lamellae. These crystal defects could act as heterogeneous nucleation sites, lowering the energy barrier of Ti2AlC precipitated from the lamellar matrix during the isothermal annealing stage. The dispersed Ti2AlC particles, with an average size of 45 ± 15 nm, showed the following coherent relationship with the lamellar matrix, [1‾216‾]Ti2AlC//[001]γ and (101‾0)Ti2AlC//(2‾20)γ.

A Novel Insight Toward Zr Poisoning on Grain Refinement of Al–5Ti–1B and Its Solution

A Novel Insight Toward Zr Poisoning on Grain Refinement of Al–5Ti–1B and Its Solution

Role of nitrogen and tantalum in the high-temperature oxidation behavior of AlCoCr0.5NiTaxTi(N) alloys synthesized by laser in situ synthesis

Laser cladding was used to synthesize the coatings of the AlCoCr0.5NiTaxTi (N) alloys on a Ti–6Al–4 V substrate. As the Ta content increased, the alloy evolved from columnar crystals composed of dendritic face-centered cubic (FCC)/L12 phases and interdendritic Laves phases to a eutectic structure. The high-valence state of Ta diminished oxygen vacancies in TiO2, which reduced the diffusion rate, so an appropriate Ta content improved high-temperature oxidation resistance. In the cladding process, nitrogen from the protective gas was partially dissolved in the alloy and partially formed Ti2N, both of which act as diffusion barriers for titanium, inhibiting the formation of titanium oxide and promoting the formation of continuous single aluminum oxide, thereby improving oxidation resistance at high temperatures.

High‐Dissolution Mechanism of Ti–48Al–2Cr–2Nb Alloy in Electrochemical Machining from a Nonlinear Dynamic Perspective

High‐rate dissolution process of Ti–48Al–2Cr–2Nb alloy in electrochemical machining exhibits strong nonlinear dynamic characteristics, but the quantitative relationship between these nonlinear characteristics and surface topography, as well as the electro‐dissolution mechanism, is unknown. Therefore, the fractal and recursive features of dissolution behavior and quantitative characterization of the dissolved surface topography were investigated. Additionally, an electro‐dissolution mechanism model in electrochemical machining process was presented. Applying a higher potential of 11 V can enhance the stability of the electrochemical system, resulting in a smoother and uniform surface. The saturation correlation dimension, surface roughness, and integral area of lacunarity initially decrease before increasing with higher electrolytic pressure, while laminarity and determinism show an initial increase followed by a decrease. These five characteristic parameters reach their optimal values at an electrolyte pressure of 0.4 MPa, indicating that achieving a stable and deterministic electrochemical system is crucial for obtaining a uniform smooth surface. These nonlinear dynamic characteristic parameters can be considered as in‐situ monitoring parameters for surface quality in ECM. The anodic dissolution process comprises three stages: initial passive film dissolution and breakdown, rapid dissolving with surface coarsening, and stable dissolving with polishing.

Exploiting top ductile B2/β layers to in-situ cold-forging Ti–22Al–25Nb alloy manufactured by laser melting deposition

Ti–22Al–25Nb intermetallic alloy is the latest generation of lightweight aerospace material with superior high-temperature performance. In the present study, a novel hybrid 3D-printing technique, point-forging and laser-deposition (PF-LD), was adopted for demonstrating its possibility in the preparation of near-net-shaping Ti–22Al–25Nb component. We innovatively exploited the top ductile B2/β-phase-zone as a natural protective layer, successfully preparing Ti–22Al–25Nb intermetallic parts with relatively larger build-height without initiating any macro-micro cracks. Three groups of control trials were further performed to ascertain the effect of initial laser parameters on microstructural characteristic and mechanical performance. Among three deposition strategies, the sample with intermediate laser scanning rate reached the best combination of ultimate tensile strength (UTS: ∼ 1280.7 MPa) and elongation after failure (EL: ∼ 5.7 %), while superior tensile strength (UTS: ∼ 1314.8 MPa) could be also achieved at the expense of tensile ductility (EL: ∼ 2.4 %). This study not only reveals a new idea to low-temperature forming Ti–22Al–25Nb alloy, but also provides an insight into the relationship between PF-LD processing parameters and mechanical performance.

Mesoporous Mg–Al–Ti composite oxide incorporated mixed matrix ultrafiltration membrane with superior multi-heavy metal removal capacity, anti-fouling & anti-microbial property

Mesoporous Mg–Al–Ti ternary composite oxide nano-adsorbents have demonstrated an exceptional performance to remove multiple heavy metals (As, Pb, Cd, Cr). Incorporation of these nanoparticles (NPs) in polysulfone membrane created a multifunctional mixed matrix membrane (MMM) with heavy metal adsorption capacity (both cationic and anionic species), enhanced hydrophilicity, anti-fouling property, and anti-microbial activity. The best heavy metal removal performance was shown by the membrane incorporated with 0.8 wt% NPs. Hydrophilicity improvement was studied through the decrease in water contact angle from 71° to 57° and surface probing using atomic force microscopy (AFM). With a maximum As(III) adsorption capacity of 256.6 mg/g, the membrane had a breakthrough volume of 25L and could provide safe drinking water for 19 h from a real Arsenic (As) contaminated groundwater sample with a flux of 48 l/m2-h. Beyond that, >90 % removal of Cd, Pb & Cr was also observed with maximum adsorption capacity of 652.9 mg/g, 332.5 mg/g, and 89.4 mg/g respectively. 92.5 % flux recovery after filtering a 1000 ppm bovine serum albumin showed the anti-fouling property. Successful inhibition of both gram-positive and gram-negative bacterial growth, and >99.99 % removal of colony forming units (CFU/ml) in the filtration process confirmed the anti-microbial resistance. With its multifunctionality, these membranes hold great potential for practical water treatment applications.

Optimization of hot-rolling parameters for a powder metallurgy Ti–47Al–2Cr–2Nb-0.2W alloy based on processing map and microstructure evolution

In this work, a two-stage rolling method with varied temperature and strain rate was proposed for powder metallurgy (PM) Ti–47Al–2Cr–2Nb-0.2W alloy sheets based on the guidance of processing map and microstructure evolution. Compared with conventional rolling at a high temperature and a low strain rate, the TiAl alloy exhibited enhanced plastic deformability through the implementation of the two-stage rolling method, resulting in a higher cumulative true strain. Microstructure analysis revealed significant grain refinement in the rolled sheet. During the first stage of hot rolling with high temperatures and low strain rates, the softening behavior caused by dynamic recovery (DRV) and dynamic recrystallization (DRX) is conducive to the plastic deformation in the second stage rolling (low temperatures and high strain rates). In addition, the formation of mechanical twins further promotes DRX behavior. The softening mechanism of α2 phase is DRV, and that of γ phase is continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX).

Eliminating cracks in Ti–47Al–2Cr–2Nb/Ti–6Al–4V micro-laminated composites fabricated by dual-material laser powder bed fusion

The low ductility of titanium aluminide at room temperature has been one of the factors that severely limit its applications. In this study, Ti–6Al–4V (Ti64) alloys were combined with Ti–47Al–2Cr–2Nb (TiAl) alloys to make micro-laminated composites with optimal ply configurations to eliminate crack formation in TiAl and improve the ductility. A dual-material laser powder bed fusion (LPBF) system was used to fabricate the TiAl/Ti64 micro-laminate samples. The presence of cracks, elemental composition and mechanical properties were experimentally characterised and analysed to understand the effect of ply configuration and the mechanism of eliminating cracks. It was found that smaller TiAl ply thickness and lower TiAl volume fraction result in fewer cracks formed in the micro-laminates. Elemental composition analysis reveals that the Al content in the first two powder layers (i.e., 200 μm thick in total) of a TiAl ply is reduced to 10%–35% due to the partial mixture of the TiAl ply and the proceeding Ti64 ply in the LPBF. The reduced Al content leads to combined α-Ti, β-Ti and α2-Ti3Al phases instead of γ-TiAl phases, thus eliminating the formation of cracks within the first 200 μm thick region of the TiAl ply. This study demonstrates that crack-free and dense TiAl/Ti6 micro-laminated composites can be produced with the TiAl ply thickness reduced to 200 μm and the TiAl volume fraction reduced to 25% (Ti64 ply thickness 400 μm). Ductility of the crack-free micro-laminates at room temperature is comparable to or even exceeds the properties of TiAl/Ti64-type laminates made by other manufacturing processes, which may imply good machinability. Note that further research is required to investigate the properties and applications of the micro-laminates at elevated temperatures.

Hybrid manufacturing approach for landing gear applications: WAAM Ti–6Al–4V on forged Ti–5Al–5Mo–5V–3Cr

High-strength metastable β-titanium alloys like Ti-5553 (Ti–5Al–5Mo–5V–3Cr) are frequently used in highly loaded aerospace components. Such aerospace parts tend to be expensive to traditionally manufacture due to current industry process limitations such as inflexibility for complex geometries, costs related to tooling for large forgings, extended lead times, poor machinability and high material waste. These challenges are leading to increased interest in exploring alternative manufacturing routes. This work investigates the use of additive manufacturing to deposit cost-effective and machinable Ti-64 (Ti–6Al–4V) alloy onto a forged Ti-5553 alloy substrate. The microstructure evolution, microhardness and tensile properties have been investigated for both the as-deposited as well as for stress relief heat-treated conditions. The results confirmed the formation of coarse columnar β grains with a fine basketweave α structure. The heat affected zones (HAZs) developed in the Ti-5553 substrate material from the cyclic thermal fluxes introduced from the melt-pool were characterized by a gradient microstructure of dissolving constituent phases with nearing proximity to the fusion zone. Tensile testing in the as-deposited condition was characterised with a UTS of 884 MPa and a ductility of 15%. Tensile samples extracted across the substrate-deposit interface all failed in the WAAM Ti-64 material and demonstrated comparatively greater strength but poorer ductility. A band of tensile residual stresses was imparted along the substrate, but was adequately stress relieved after heat-treatment at 600 °C. The heat-treatment led to the formation of more homogeneous α-phase laths throughout the HAZ of the Ti-5553 material and provided overall improvements to the strength and ductility.

Generalized stability criterion for columnar to equiaxed grain transition during solidification upon vertical twin roll casting

To promote the columnar to equiaxed grain transition (CET) to obtain uniform equiaxed grain, most of the available theoretical works mainly focus on the growth but ignore the nucleation. Regarding it, a systematical framework integrating nucleation catalyzed by refiners with dendritic growth, was constructed, where, a new conception of generalized stability (GS), considering evolving thermodynamic driving force (ΔG) and kinetic energy barrier (Q) upon solidification of VTC, was adopted to study the CET position, the grain radius and the mechanical properties. By adding the refiners, especially the Al–5Ti–1B refiner, the larger thickness of 5–6 mm for equiaxed grain and finer grain radius of 19 μm are exhibited by increasing the ΔG for nucleation and the GS for growth, possessing simultaneously improved strength and plasticity. Following a criterion of high ΔG–high GS, the refiner diameter is optimized to be 0.3 μm.

The Archaeology of Hellenism: Olympia and the Presence of the Past

Abstract Olympia holds a central place in conceptions of modern sport, Hellenism, and the Olympic Games. This article traces the concurrent development of the site and Panhellenism and Hellenism through its landscape, built environment, and its reception over the past 3,000 years. By tying together Pierre de Coubertin's Olympism to the physical landscape of ancient Olympia, this article argues that the site itself has contributed, through multiple permutations and through several key changes in the early Iron Age, Roman period, and nineteenth century to the global Hellenism that is at the foundation of the modern Olympic Games.

Metal-Doped NASICON/Polymer Composite Solid Electrolyte for Lithium Titania Anode in Lithium-Ion Batteries.

This study reports five types of metal-doped (Co, Cu, Sn, V, and Zr) NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP)/polymer composite solid electrolytes (CSEs) enabling Li4Ti5O12 (LTO) anodes to have high rate capability and excellent cycling performance. The high Li+-conductivity LATP samples are successfully synthesized through a modified sol-gel method followed by thermal calcination. We find that the cation dopants clearly influence the substitution of Al for Ti, with the type of dopant serving as a crucial factor in determining the ionic conductivity and interfacial resistance of the solid electrolyte. The CSE containing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and Sn-LATP shows an ionic conductivity of 1.88 × 10-4 S cm-1 at ambient temperature. The optimum conductivity can be attributed to alterations in the lattice parameters and Li+ transport pathways owing to Sn doping. The solid-state cell equipped with the LTO-supported CSE containing Sn-LATP fillers demonstrates both excellent high rate capability at 5 C (with a capacity retention of 86% compared to the value measured at 0.2 C) and superior cycling stability, maintaining high Coulombic efficiency (>99.0%) over 510 cycles. These findings indicate that the proposed CSE is highly promising for use in solid-state lithium batteries with desirable charge-discharge properties and high durability.

Additive technologies of producing titanium aluminide based alloys

Additive technologies of producing titanium aluminide based alloys

Визначення власних частот та форм коливань лопатки турбіни, виготовленої зі сплаву на основі алюмініду титану

This paper investigates the possibility of manufacturing the working blade of the 2nd stage of the free turbine from an experimental alloy based on titanium aluminide of the Ti-28Al-7Nb-2Mo-0.3 (Y, Re, B) system. Alloys of this class are important structural materials with a unique set of physical and mechanical characteristics. Alloys based on aluminide are characterized by low density, high heat strength, and heat resistance and have a high potential to replace nickel-based alloys designed for operation at temperatures no higher than 850°C. However, the use of a new alloy for the manufacture of a turbine blade involves calculations of the strength and oscillations of the blades. The purpose of the calculations is to determine the possibility of using an aluminide-based alloy of the Ti-28Al-7Nb-2Mo-0.3 (Y, Re, B) system instead of the VZHL12E-VI alloy for the selected working blade. The research was carried out by performing a modal analysis, determining the stress-deformed state, and checking the strength and mass characteristics. The physical properties of the materials were used as the initial data for the calculation. The geometry and temperature distribution of the blade and its fixing remained constant for the two options. A three-dimensional model of the experimental vane was built using the Unigraphics NX system, and a finite element model was developed using the Ansys software complex. It was established that when an experimental alloy is used, the mass of one blade is reduced by almost 40%. Using the finite element method, the natural frequencies and forms of blade oscillations were calculated, and Campbell’s diagrams were constructed for the original and experimental blades for the nominal operation of the engine. When using an experimental alloy, the frequencies of the blades’ natural oscillations are further from the resonant frequency. The distribution of equivalent stresses was determined, and it was shown that the maximum stresses act in the root section of the blade feather. When using the experimental alloy based on titanium aluminide, the equivalent stresses are reduced by 35% compared with the initial values. It is shown that the safety margin of the proposed material is not less than that of the VZHL12E-VI alloy.