TiAl Research Articles

Analysis of the Structure and Properties of As-Built and Heat-Treated Wire-Feed Electron Beam Additively Manufactured (WEBAM) Ti–4Al–3V Spherical Pressure Vessel

In the present work, a high-pressure spherical vessel was fabricated from Ti–4Al–3V titanium alloy using wire-feed electron beam additive manufacturing and characterized for tightness at high pressure. Studies have been carried out to characterize the microstructures and properties of the vessel’s material in four states: as-built (BM), annealed at 940 °C with cooling in air (HT1 treatment), quenched in water from 940 °C (HT2 treatment), and quenched with subsequent annealing at 540 °C (HT3 treatment). The microstructure of the as-built (BM) samples was composed of grain boundary α-Ti and α/β lath colonies located within the columnar primary β-Ti grain boundaries. The ultimate tensile strength of the as-built material was in the range of 582 to 632 MPa, i.e., significantly lower than that of the source Ti–4Al–3V alloy wire. The subtransus HT1 heat treatment allowed β→α″ transformation, while both HT2 and HT3 resulted in improved tensile strength due to the transformation of β-Ti into α/α′-Ti and the decomposition of α′ into α/β structures, respectively.

Novel orientation relationships and mechanical properties of in situ synthesized Ti5Si3-reinforced TiAl composite via electron beam-directed energy deposition

Titanium aluminide (TiAl) alloys, known for their light weight and high specific strength, hold promising potential for aerospace applications. Recent studies have focused on improving their properties through composite strengthening. An in situ synthesized Ti5Si3-reinforced TiAl composite with excellent performance was successfully fabricated via a dual-wire electron beam-directed energy deposition (EB-DED) process. The microstructure of the as-deposited Ti5Si3/TiAl composite consisted of primary Ti5Si3 rods, eutectic Ti5Si3 needles, and lamellar TiAl+Ti3Al structures. The phase transformation during the EB-DED process was L→Ti5Si3+L→Ti5Si3+(α+Ti5Si3)Eutectic→Ti5Si3+(Ti3Al+TiAl)Eutectoid. The expanded Blackburn orientation relationships among the ternary phases emerged from the eutectic reaction of L→α+Ti5Si3 with an undercooling exceeding 136°C and the subsequent eutectoid reaction with ordering transformation and were expressed as <112¯0>Ti3Al//<101¯0>Ti5Si3//<11¯0]TiAl and {0001}Ti3Al//{0001}Ti5Si3//{111}TiAl. The Ti5Si3 phase had a greater hardness than did the lamellar structures and enhanced the mechanical properties of the matrix. The compressive yield strengths at room temperature and 750°C were 1221±51 and 1034±34 MPa, respectively, whereas the tensile yield strength was 347.4±12.7 MPa at 950°C, surpassing those of other TiAl alloys. The calculated strength with different strengthening mechanisms was 1056.4 MPa, and the greatest improvement in strength was attributed to the decreased interlamellar spacing. This work provides critical insight into the design of TiAl composites with superior mechanical properties and aids in understanding the microstructural evolution of as-deposited Ti5Si3/TiAl composites.

On the Effect of Chemical Heterogeneity on the Shape Memory Performance of Fe–Ni–Co–Al–Ti Single Crystals

AbstractThe present work focuses on the formation of the γ′-phase and its impact on the functional properties of a Fe-28Ni–17Co–11.5Al–2,5Ti (at.-%) shape memory alloy (SMA) under cyclic loading conditions at different testing temperatures. The effect of aging treatments conducted in a wide range of aging temperatures and times was investigated. While specific heat treatments, namely 600 °C for 4 h, result in excellent superelastic properties with a fully reversible material response in single cycle experiments, interestingly, functional degradation is found to be more pronounced under cyclic loading compared to other derivatives of the Fe–Ni–Co–Al-based SMA systems. In addition to mechanical testing, a detailed microstructural analysis was conducted using transmission electron microscopy. The results of the present study clearly reveal that chemical inhomogeneities have to be carefully considered for the characterization of the functional performance of these iron-based SMAs. Chemical heterogeneities are not only identified as the underlying microstructural mechanism for the pronounced cyclic degradation behavior, but are also supposed to have a significant influence on the precipitation kinetics of the γ′-phase.

High cycle fatigue properties of Ti-48Al-2Cr-2Nb alloy additively manufactured via twin-wire directed energy deposition-arc

Recently, additive manufacturing for titanium aluminide has received sustained attention. Considering the extensive applications on low pressure turbine blades in aerospace field, dynamic mechanical properties of titanium aluminide, especially the fatigue properties, are of great importance. In present work, fatigue test at ambient temperature was conducted for the first time on twin-wire directed energy deposition-arc (TW-DED-arc) fabricated Ti-48Al-2Cr-2Nb alloy with equiaxed lamellar colonies. More detailed researches on fatigue fracture characteristics and deformation modes are also investigated. The experiment results indicate that TW-DED-arc fabricated Ti-48Al-2Cr-2Nb alloy exhibits flat S–N behavior with a good resistance to fatigue. Fatigue life fluctuates widely at same stress level, but such fluctuations gradually weaken as stress decreases. Furthermore, γ/α2 interface and lamellar colony boundary as well as special microstructures of as-fabricated Ti-48Al-2Cr-2Nb alloy are weak areas during fatigue process, which easily become crack nucleation sites. As stress level decreases, deformation mode of as-fabricated Ti-48Al-2Cr-2Nb alloy translates from twinning and dislocation slip to predominantly dislocation slip. In general, these findings provide an important reference for engineering applications of titanium aluminide.

Coupling CALPHAD Method and Entropy-Driven Design for the Development of an Advanced Lightweight High-Temperature Al-Ti-Ta Alloy.

In this study, a new lightweight Al-Ti-Ta alloy was developed through a synergistic approach, combining CALPHAD methodology and entropy-driven design. Following compositional optimization, the Al87.5Ti6.25Ta6.25 (at.%) alloy was fabricated and isothermally heat-treated at 475 °C for 24 h to attain equilibrium. X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses revealed a dual-phase microstructure comprising a 50 vol.% FCC matrix enriched in Al and 50 vol.% Al3(Ti,Ta)-type intermetallic phase (IP). Notably, the FCC phase exhibited a high-melting transition temperature of 660 °C, surpassing conventional Al-Si cast alloys. Phase-specific nanomechanical properties were evaluated using Nanoindentation. Microindentation tests demonstrated exceptional microhardness of approximately 3300 MPa. These results indicate the alloy's superior hardness compared to conventional alloys such as Al-Si (A390), 7075 Al alloy, and CP-Ti, even exceeding Ti-64 alloy at a 15% lower density. The alloy's stability under prolonged heat treatment at 475 °C, reflected by stable phases, microstructure, and mechanical properties, highlights its enhanced thermal stability, which can be attributed to entropy-driven phase stabilization. This study underscores the effectiveness of integrating entropy-driven design strategy with CALPHAD predictions for the accelerated development of advanced Al-based alloys.

Ti1-xAlxN or TiN + AlN: An investigation about Al influence on titanium aluminum nitride thin films structural organization

Ti1-xAlxN thin films with different Al contents (Ti0.8Al0.2N, Ti0.6Al0.4N and Ti0.4Al0.6N) were deposited by reactive magnetron sputtering in order to determine the real structure formed in these coatings: a single ternary nitride, with a substitutional solid solution formation, or the presence of two binary nitrides, TiN + AlN. The elementary composition, morphology homogeneity, chemical elements distribution, crystalline structure, grain size evaluation, modification on coatings structure and formed compounds were determined. GAXRD analyses evinced a grain size growth for all Ti1-xAlxN samples, suggesting that aluminum atoms are not present as a single AlN phase, but as a ternary nitride. In XPS analyses, N 1s spectrum for all samples exhibited a shift toward lower binding energies in Ti-N component, attesting the Ti-Al-N bond presence. Moreover, signatures of Al 3p and Ti 3d band shift were detected in the valence band region, confirming the Ti1-xAlxN solid solution formation for all deposited samples.

Enhanced vacuum brazing joining between Ti–48Al–2Cr–2Nb/Ti–22Al–25Nb intermetallic alloys by Zr-free Ti-based filler

This study investigates the microstructure and tensile properties of vacuum-brazed joints of Ti–48Al–2Cr–2Nb (Ti4822) and Ti–22Al–25Nb (Ti2AlNb) intermetallic alloys using Ti-based filler metals, with and without the addition of Zr element. Detailed microstructural characterization of the brazed joints was conducted using Electron Backscatter Diffraction and Transmission Electron Microscopy, identifying various phases and their distributions. The tensile properties were tested at room temperature and at 650 °C, revealing the influence of Zr on the mechanical performance of the joints. The results demonstrated that the microstructure of joints brazed with Zr-containing filler metals exhibited a layered structure with brittle Zr-enriched intermetallic compounds, limiting their mechanical properties. Conversely, Zr-free filler metals yielded more homogeneous and ductile microstructures, significantly improving tensile strength and elongation. The Zr-free joints obtained after holding at 980 °C for 60 min exhibits the highest tensile strength, reaching 368.23 MPa at room-temperature and 293.46 MPa at 650 °C, respectively. These findings provide valuable insights for optimizing brazing processes and filler metal compositions to enhance the performance of TiAl-based intermetallic alloy joints.

Studies on hardness, elastic modulus and high temperature oxidation resistance of TiC and TiB2 dispersed titanium aluminide (Ti45Al5Nb0.5Si) composites developed by laser direct energy deposition

In this study, TiC (5 to 10wt.%) and TiB2 (5 to 10wt.%) reinforced TiAl (Ti45Al5Nb0.5Si) composites have been developed by laser direct energy deposition (LDED) process. The microstructures of TiAl/TiC and TiAl/TiB2 composites consist of TiC and TiB2 particles dispersed in γ and α2 matrix. The microhardness of the composites is improved from 571 HV to 634-683 HV (for TiC dispersion) and 649-694 HV (for TiB2 dispersion). The activation energy of cyclic oxidation is increased from 228kJ/mol (Ti45Al5Nb0.5Si) to 271-301kJ/mol (TiC dispersion) and 262-296kJ/mol (TiB2 additions). The mechanism of oxidation of the composites is established.

Microstructural evolution and mechanical property of high-strength metastable β titanium alloy joint via electron beam welding

Obtaining a fundamental understand of the relationship between weld microstructure and mechanical properties is critical for ensuring a high weld quality. This work explored the micro-mechanism responsible for the mechanical properties of a 10-mm-thickness metastable β titanium alloy (Ti–3Al–5Mo–4Cr–2Zr–1Fe, wt.%) joint welded by electron beam welding (EBW). Weld microstructure and its evolution behavior were revealed by means of multi-scale microstructure characterization. Obtained results indicate that the absence of α phase and formation of nano-scale ω particles occurred in the coarse columnar β grains of the fusion zone (FZ). Intense dissolution and significant coarsening of secondary α phase occurred in the heat affected zone. Between the FZ and HAZ, a partially melted zone was observed and contains few equiaxed β grains. Compared to the base material, the as-welded EBW joint shows significant softening in weld seam and a slight decrease of 17% in ultimate tensile strength, while a severe reduction of 73% in elongation. It was observed that majority of plastic deformation is confined to the narrow FZ, indicating a significant localization of tensile strain. This leads to premature fracture of the joint within the FZ and consequently to significant deterioration of the overall ductility. This work contributes to advancing the understanding of the role of microstructural evolution on the mechanical properties of high-strength titanium alloy joints via EBW.

Effect of Ca Addition on Inclusions, Microstructures, and Impact Toughness of Coarse‐Grained Heat‐Affected Zone After High‐Heat Input Welding in Mg‐Deoxidized Shipbuilding Steel Plates

Effect of Ca addition on inclusions, microstructures, and impact toughness of coarse‐grained heat‐affected zone (CGHAZ) in Mg‐deoxidized shipbuilding steel plates after high‐heat input welding (HHIW) of 400 kJ cm−1 are investigated. Characteristics of inclusions and their effect on microstructures and impact toughness are elucidated. With the addition of Ca, number density of inclusions decreases from 384 to 273 mm−2, but average size increases from 1.23 to 1.32 μm. Number densities of inclusions such as MgAl2O4, MgAl2O4 + MnS, Mg–Al–Ti–O + MnS, MgO + MnS, and TiN + MnS, which are observed to induce intragranular acicular ferrites (IAFs) formation, decrease from 3.0, 15.3, 18.8, 16.5, and 18.1 to 0.2, 1.2, 4.4, 3.0, and 6.3 mm−2, respectively. Observed Ca‐containing inclusions of diameter over 2.5 μm in Mg–Ca steel cannot serve as the effective nucleation sites for IAFs formation. Contents of IAFs and polygonal ferrites decrease from 73.20% and 19.96% to 54.34% and 5.63%, respectively. Frequency of high‐angle grain boundaries decreases from 70.5% to 51.3%. The CGHAZ fracture morphology changes from ductile fracture to brittle fracture with the area proportion of the fibrous zone decreasing from 56.5% to 0%. Hence, the impact toughness of CGHAZ decreases significantly from 175 to 23 J at −20 °C after HHIW.

Facile production of titanium aluminide intermetallic powder for powder metallurgy and metal additive manufacturing

Facile production of titanium aluminide intermetallic powder for powder metallurgy and metal additive manufacturing

Effect of multidirectional forging on grain structure and mechanical properties of hypereutectic Al–20%Si alloys with added refiners and modifiers

ABSTRACT The present work is focused on the multidirectional forging (MDF) of Al–20 wt-% Si alloys with the addition of refiners and modifiers. The MDF process was performed at 200°C with a cumulative strain of 0.63. Microstructural characterization and mechanical performance were evaluated on the Al–20Si, Al–20Si–4.5Cu, Al–20Si–4.5Cu–1(Al–Ti–B), Al–20Si–4.5Cu–1(Al–Ti–B)–10(Al–Sr). The microstructure analysis revealed significant changes in the eutectic and primary phase refinement. The micro-Vickers hardness confirmed that the MDF process resulted in increased hardness (125 ± 1.9 VHN) compared to the homogenized samples (96 ± 2.7 VHN). Tensile test results showed that with the accumulation of strain, ultimate tensile strength increased to 435 MPa from 302 MPa with reduction in the percentage of elongation from 7.8 to 5.6. The grains were more uniformly distributed with addition of modifiers, and refiners further reduced the nucleation number of eutectic grains. The wear study demonstrated that the wear resistance is more in the Al–Si-Cu-Sr sample due to the increased level of hardness. The combination of multidirectional forging techniques with judicious incorporation of refiners and modifiers engenders a synergistic enhancement of microstructural integrity, hardness profiles, and wear-resistant properties in hypereutectic Al-20Si alloys.

The microstructural development and erosion mechanism of BaZrO3/Al2O3 double ceramics by Ti–46Al–8Nb alloy melt

In this study, the erosion of BaZrO3/Al2O3 double ceramics by Ti–46Al–8Nb alloy melt was investigated at different melting temperatures (1833 K, 1873 K and 1913 K) and time (1800 s, 3600 s, 5400 s and 7200 s). The microstructure of erosion layer and the alloy ingot were analyzed as well as the oxygen content of the alloy ingot. The erosion mechanism was clarified in the kinetic perspectives. The results showed that the new oxide BaAl2O4 production was attached on the ingot surface, and two kinds of inclusions, i.e., (Ti, Zr)5(Si, Al)3 and YAlO3, were formed in the ingot matrix. The thickness of erosion layer, the oxygen content of ingot, and the volume fraction of inclusions increased with increasing melting temperatures and time. In addition, these three phenomena were controlled by the kinetics of dissolution, and the time exponents were approximately equaled to 0.5, indicating that the erosion mechanism was dissolution controlled by mutual diffusion between the double ceramics and alloy melts. The activation energies of three phenomena were determined by Arrhenius equation, and three kinetic models were further established.

Fatigue properties of a Ti–5Al–5Mo-5 V–3Cr alloy manufactured by electron beam powder bed fusion

AbstractAdditive manufacturing (AM) is a modern way of manufacturing structures, which tends to have fewer design limitations than those manufactured by conventional processes such as casting or forging. A combination of high-strength materials and small and complex structures opens up a wide range of potential applications, especially in the fields of medicine and aerospace. Titanium and its alloys show a very beneficial combination of density and mechanical properties. One of these alloys is the metastable β titanium alloy Ti– 5Al–5Mo–5 V–3Cr (Ti-5553), which is currently used mainly for large forged structures like landing gears of airplanes. In this study, for the first time the fatigue behavior of electron beam powder bed fused (PBF-EB) Ti-5553 was investigated with a focus on the defects created by the layer wise manufacturing. To understand the defect structure and its respective influence on the fatigue behavior, all specimens were scanned prior to fatigue testing using a state-of-the-art µ-focus CT. The specimens were subjected to two heat treatment procedures commonly used in technical applications, which were aiming for high strength (solution treated and aged—STA) as well as high ductility (beta annealed, slow cooled and aged—BASCA). Results indicate that the fatigue strength of PBF-EB manufactured Ti-5553 is significantly reduced compared to conventionally manufactured Ti-5553. The main reason for this are defects, which have varying critical effects depending on the heat treatment of the specimen and the defect size, shape, location and type.

Reconstructing the soundscape of the ancient Hippodrome of Olympia for an immersive sonic experience of heritage sites based on sound source description in texts

This study attempts to reconstruct and auralize the soundscape of the Hippodrome of Olympia in Greece. This UNESCO world-heritage-listed-site is considered the evidence of the Greek hippodromes. Hippodromes used to have several activities from which different combinations of sound sources created the soundscape. To collect sound sources, description in texts of site is sought by implementing methods of the archaeology of soundscape and the suggested criteria of contextual, internal, and comparative certainty for archaeoacoustics studies. The description of these activities facilitates reconstructing and auralizing the soundscape during different phases of events in the hippodrome. The results of the study showed that the information about the activities on the hippodrome, on similar hippodromes of different civilizations, and on similar hippodromes of later eras are rather sufficient to create a comprehensive soundscape of the site. Auralizing the reconstructed soundscape by using current auralization software and techniques promises of immersive experience of ancient sites that enhances understanding the sonic intangible cultural heritage element and the experience of the ancient soundscape. Furthermore, ancient users' perception of the soundscape can be approached by localizing the sound sources on the site and obtaining the corresponding acoustical properties, providing information of users' response to the sonic outcomes

Comparative analysis of ternary TiAlNb interatomic potentials: moment tensor vs. deep learning approaches

Intermetallic titanium aluminides, leveraging the ordered γ-TiAl phase, attract increasing attention in aerospace and automotive engineering due to their favorable mechanical properties at high temperatures. Of particular interest are γ-TiAl-based alloys with a Niobium (Nb) concentration of 5–10 at.%. It is a key question how to model such ternary alloys at the atomic scale with molecular dynamics (MD) simulations to better understand (and subsequently optimize) the alloys. Here, we present a comparative analysis of ternary TiAlNb interatomic potentials developed by the moment tensor potential (MTP) and deep potential molecular dynamics (DeePMD) methods specifically for the above mentioned critical Nb concentration range. We introduce a novel dataset (TiAlNb dataset) for potential training that establishes a benchmark for the assessment of TiAlNb potentials. The potentials were evaluated through rigorous error analysis and performance metrics, alongside calculations of material properties such as elastic constants, equilibrium volume, and lattice constant. Additionally, we explore finite temperature properties including specific heat and thermal expansion with both potentials. Mechanical behaviors, such as uniaxial tension and the calculation of generalized stacking fault energy, are analyzed to determine the impact of Nb alloying in TiAl-based alloys. Our results indicate that Nb alloying generally enhances the ductility of TiAl-based alloys at the expense of reduced strength, with the notable exception of simulations using DeePMD for the γ-TiAl phase, where this trend does not apply.

Impact of sulfate to chloride ratio on titanium aluminide coating's high temperature corrosion performance in settings mimicking waste incineration

One major problem with waste incineration is the corrosion of superheater tubes at high temperatures. The presence of sulfate and chloride in this setting poses a severe risk to the boiler's service life. In this work, pack aluminizing was used to prepare titanium aluminide coatings, which was then subjected to five distinct NaCl+Na2SO4 salt combination proportions for 168 h at 600 °C. The outcomes demonstrated that in the presence of solid Na2SO4 deposits, titanium aluminide coatings displayed remarkably low corrosion rates. Adding 1/6 NaCl significantly accelerated the rate of corrosion. The electrochemical corrosion resulting from eutectization between NaCl and Na2SO4 was again considerably amplified when the NaCl level was raised to 1/4.

Direct Synthesis of Ti-Al Compound Powders by Electrolysis in Molten LiCl-KCl

The deposition potential difference between Ti and Al is only 70 mV. The deposition reaction of Ti-Al compound happens at the potentials slightly higher than that of metallic Ti and Al. Through galvanostatic electrolysis of mixture solution of Al and Ti ions, all kinds of titanium aluminides can be directly synthesized. The composition of the product compound can be selected through adjusting the combination of Ti and Al ions in the electrolyte.

Effect of process parameters of selective laser melting on the structure, texture, and mechanical properties of an alloy based on orthorhombic titanium aluminide Ti2AlNb

Effect of process parameters of selective laser melting on the structure, texture, and mechanical properties of an alloy based on orthorhombic titanium aluminide Ti2AlNb

Microstructural Evolution, Precipitation Behavior, and Mechanical Property Response of Cast Al–Li–Cu–Cd–Mn–Zr–Ti Alloy

The microstructural evolution and mechanical properties of cast Al–Li–Cu–Cd–Mn–Zr–Ti alloy during heat treatment are investigated systematically. In these findings, it is shown that the as‐cast alloy exhibits fine and equiaxed grains. During the solid solution treatment, Al20Cu2Mn3 dispersoids effectively restrict grain growth, and reducing the solid solution time has a similar effect. Subsequently, the precipitation behavior and its effect on the mechanical properties during the aging process are revealed. Al3(Ti, Zr) particles are uniformly distributed throughout the matrix, acting as nucleation sites for δ′, θ′, and T1 precipitates. Overtime, δ′ precipitates gradually coarsen and decrease in number, and some δ′ precipitates attach to Al3(Ti, Zr) particles, forming core–shell Al3(Li, Ti, Zr) phases. At the same time, plate‐shaped θ′ and T1 precipitates emerge and coarsen. After aging at 160 °C for 24 h, the alloy exhibits an excellent combination of strength (yield strength =293.3 ± 4 MPa, ultimate tensile strength =468.0 ± 3 MPa) and ductility (elongation =9.6 ± 0.4%), surpassing those reported in other cast Al–3Li–2Cu–X alloys. Critically, the underlying mechanisms behind the microstructure and mechanical properties are discussed extensively, providing valuable insights for the advancement of cast Al–Li alloys.