Ti-Al System Research Articles

Density and surface tension of liquid Al, V and their binary alloys measured by electromagnetic levitation

Both density and surface tension were systematically investigated over a wide temperature and compositional range for the liquid Al–V alloy system. The thermophysical properties were measured in an electromagnetic levitation device. A linear decrease in surface tension and density with increasing temperature was observed for every alloy composition investigated. Additionally, a decrease in density and surface tension was observed for increasing aluminum content among the different probed samples. This decrease is, a strong deviation from an ideal mixing behavior which was experienced for both properties. Different models, including variants of the well-established Butler model, were employed to better describe the compositional dependence of density and surface tension in the liquid Al–V system. The advantages and disadvantages were discussed for each model describing the measured thermophysical property data. Strong similarities were observed when comparing the mixing behavior and segregation effects of the investigated Al–V system with already established works for the liquid Al–Ti system. The results suggest that both vanadium and titanium show similar mixing behavior when alloyed with aluminum.

Thermodynamic Assessments of Ti-Al, Ti-Fe, and Ti-Al-Fe Systems with Four-Sublattice Description of Ordered Body-Centered Cubic Phase and Density Functional Theory Data

A thermodynamic description of the Ti-Al-Fe system was established with reassessed Ti-Al and Ti-Fe binary systems using density function theory (DFT) data. All stable and metastable end members of BCC_B2, BCC_D03/B32, BCC_L21, inverse BCC_L21, Laves C14, D019-Ti3Al, L10-TiAl, Ti Al2, Ti3Al5, D022-TiAl3, τ2 and τ3 in the Ti-Al, Ti-Fe and Ti-Al-Fe systems were energetically defined with available experimental data and DFT calculations, reaching reasonable consistency. The ternary description was used to successfully calculate the A2-B2-L21 transformation in Fe-rich corner and A2-B2 transformation in Ti-rich corner, allowing the design of Ti-rich and Fe-rich alloys in this system.

Effect on wetting properties of the Al-Ti system by the addition of different alloying elements

With lightweight and high-strength, Al-Ti composites have become one of the indispensable materials in the aerospace and automotive manufacturing fields. However, due to strong interfacial reactions, the traditional pure Al-Ti composites have been limited in practical applications. To better control the interfacial reaction between the reinforced phase and the matrix in the Al-Ti composites, in this paper, the effect on wetting behavior and interfacial properties of the Al-Ti system by the addition of different alloying elements (Si, Mg, Zn, Cu) in Al melt were systematically investigated using the sessile drop method. According to the results, adding Si, Mg, Zn, and Cu elements to the Al melt can increase the steady-state wetting angle to varying degrees at the end of the holding period compared to the pure Al-Ti wetting but still maintains good wettability. The Mg, Zn, and Cu elements ensure good wettability and simultaneously reduce the temperature required for wetting, providing novel ideas for preparing aluminum matrix composites. All the systems in this experiment are typical of reactive wetting. The system with added Si and Cu showed a clear interfacial layer at the Al-Ti interface, which was comparatively smooth, and both the original Al-Ti reaction at the interface and the dissolution of the Ti substrate are inhibited.

In situ synchrotron X-ray diffraction study of synthesis reactions in mechanically activated Ti + Al powder mixture under linear heating conditions

In the present work, we studied the features of phase formation in mechanically activated Ti + Al powder mixture at various heating rates for the first time. The study was carried out using high-resolution diffractometry method which made it possible to study the processes of phase formation in situ at any stage of heating. It was established that ignition of the activated mixture can be initiated in the solid phase with an extremely low content of reaction products formed at the preheating stage. An increase in the heating rate leads to a decrease in the average burning rate and an increase in the ignition temperature. At high heating rates, the ignition is initiated in the presence of a liquid phase when the ignition temperatures are close to the melting temperature of aluminum. In this case, the content of reaction products formed during preheating stage is relatively high. It was found that the all main compounds presented in the equilibrium diagram of Ti-Al system are synthesized in parallel. The content of phases in the reaction products depends on the heating rate.

Metallurgical analysis of laser welded AZ31/5A06 lap joints with Ti–Ni interlayer

The presence of brittle Mg–Al intermetallic compounds (IMCs) in Mg/Al welded joints significantly degrades their mechanical properties. Understanding of the joint interfacial metallurgical reactions is essential for improving the performance of Mg/Al joints. Various single element interlayers, such as Ti, Ni, Zn, Fe, Ce and Cu, have been introduced to improve the joint performance, and the Miedema model has been applied to analyze the priority of phase generations in binary systems. However, the metallurgical reactions in the Mg/Al interface with bi-alloy interlayers cannot be fully explained using only a binary system. In this study, laser welding of AZ31-5A06 using a Ti–Ni interlayer was comprehensively investigated Then, the aggregation tendency of the elements in the Mg–Ni–Ti–Al system was explained using the Toop model and the ternary phase diagram was used to analyze the solidification process in the interlayer. With the increasing of laser power, the interlayer became from intact to incomplete, and finally completely destroyed. As a result, the Mg–Al IMCs with a thickness of 4.5 μm (1617 W) increased to 17–21 μm (1815 W) and 130 μm (2013 W) respectively. The distribution of Mg–Al IMCs also changed from being distributed between Mg-interlayer (1617 W) to being discontinuously distributed within the joint (1815 W) and continuously distributed within the joint (2013 W). When the interlayer remained intact at 1617 W, the maximum shear strength of the joint was 145.76 MPa, and the fracture exhibited a mixed fracture pattern consisting of brittle and ductile fracture. At 1617 W, the distribution of elements at the joint interface revealed that the interlayer was composed of Al, Ni, and Ti without Mg, which successfully blocked the diffusion between Mg and Al. The Gibbs free energy calculated from the Toop model indicated that the minimum Gibbs free energy of an Al–Ni–Ti system was −59.3 kJ/mol, which is lower than that of a Mg–Ni–Ti system (−48.1 kJ/mol); therefore, the Al–Ni–Ti system would be preferentially generated in the joint. The composition of the interlayer was mainly concentrated in the α-Ti and β-Ti phase region of the liquid-phase projection phase diagram and in the TiAl+τ3-Al3NiTi2 and Ti3Al+τ3-Al3NiTi2 phase regions of the isothermal cross-section phase diagram. Consequently, the interlayer consists of multiple phases such as Ti3Al, TiAl, and Al3NiTi2. The Ti3Al and TiAl with superior strength and deformability in the interlayer inhibited the generation of Mg–Al IMC, and the partially melted Ni layer facilitated the connection between Mg/Ni/Ti, thus improving the strength of Mg–Al dissimilar alloy joints.

Designing of novel microstructure and its impact on the improved service temperature mechanical performance of 2nd and 3rd generation advanced intermetallic TiAl alloys

Advanced lightweight TiAl based intermetallic systems, capable of surviving elevated temperatures, have been a topic of interest, considering their ever-increasing demands in aerospace industries. The optimization of solidification and processing methods stands as a pivotal factor in microstructural engineering for TiAl systems, aiming to attain desired mechanical properties. The present study focuses on two distinct alloy systems, a commercial grade 2nd generation, i.e., Ti–48Al–2Cr–2Nb (at. %), and a newly developed 3rd generation, i.e., Ti–45Al–2Cr-7.5Nb-0.2B (at. %) alloys. Interestingly, the variation in the solidification path, triggered by higher Nb content along with a minor amount of B, accounts for the substantial microstructural refinement for the 3rd generation TiAl alloy. Nevertheless, prominent segregation of Nb and Cr to the β0 phase is observed in both the as-cast microstructure, which restricts the applicability of the alloys. Remarkably, a novel bilamellar-biglobular (BLBG) microstructure consisting of γ and α2 phases in both lamellar and globular morphologies is achieved through heat treatment for both categories of alloy. Elevated temperature tensile testing depicts an exceptional strength-ductility combination for 3rd generation BLBG microstructure. Excellent twin-twin activity and twin-induced plasticity effect are observed to govern the deformation mechanism. Overall, the path of solidification, phase distribution, and its effect on the deformation mechanism are thoroughly analyzed, which is of particular interest from a design and application point of view.

Исследование расстеклования аморфных наночастиц титана в вакууме и в алюминиевой оболочке: молекулярно-динамическое моделирование

The process of the devitrification of titanium nanoparticles in a vacuum and in an aluminum shell was studied at heating rate of 5∙1011 K/s by the molecular dynamics method. Additional consideration of the influence of the aluminum shell is related to the solution of the issue of reducing the temperature of the initiation of the high-temperature synthesis reaction in the Ti-Al system in mixtures subjected to preliminary mechanical activation. It is shown that the change in the devitrification temperature compared to a bulk sample is inversely proportional to the particle diameter: as the particle size decreases and, accordingly, the proportion of atoms near the interface increases, the devitrification temperature increases. The presence of an aluminum shell leads to a significant increase in the devitrification temperature of titanium nanoparticles - for the considered sizes of nanoparticles (diameter from 1.75 to 11 nm) the difference was about 200 K. Thus, a decrease in the size of titanium particles and the presence of an aluminum shell increase the temperature range for the existence of the amorphous phase of titanium. The mechanisms of the nucleation of the crystalline phase in particles in a vacuum and in an aluminum shell are significantly different: in the first case, crystal nuclei are formed near the surface; in the second, on the contrary, in the bulk of the particle.

Optimizing Hydrogen Storage Pathways in Ti–Al Alloys through Controlled Oxygen Addition

In the present study, we aimed to destabilize the Ti–Al system with nonmetallic oxygen. The synthesis of α‐(Ti, Al)[O] starting from TiO2, Ti, and Al was carried out through the arc melting method, resulting in three different oxygen content levels, 3.4, 10, and 20 at%. The room temperature activation of α‐(Ti, Al)[O] was not successful, and the activation was performed at 300°C under 5 MPa H2 pressure. The structural changes after hydrogenation (maximum absorption capacity of 3.74 wt% hydrogen) arose from the transformation of α‐(Ti, Al)[O] to cubic (Ti, Al)[O]Hx (c‐(Ti, Al)[O]Hx); nonetheless, they recovered their original lattice parameters, which are meaningfully larger than those of α‐Ti, after dehydrogenation. The hydrogen storage capacities for various α‐(Ti, Al)[O] compositions generally decreased with increasing oxygen (3.4 and 10 at%) and aluminum content in the alloy. In contrast, for the compositions with a higher oxygen content of 20 at%, the hydrogen storage capacity slightly increased as the Al concentration increased: Ti0.790Al0.010O0.200 absorbed 2.91 wt% hydrogen, whereas Ti0.767Al0.033O0.200 absorbed 3.04 wt% hydrogen. The thermogravimetric analysis showed that samples with 20 at% O released hydrogen at lower temperatures even though the major phase after hydrogenation is c‐(Ti, Al)[O]Hx regardless of the oxygen content.

Elucidating Interfacial Dynamics of Ti-Al Systems Using Molecular Dynamics Simulation and Markov State Modeling.

Due to their remarkable mechanical and chemical properties, Ti-Al-based materials are attracting considerable interest in numerous fields of engineering, such as automotive, aerospace, and defense. With their low density, high strength, and resistance to corrosion and oxidation, these intermetallic alloys and metal-compound composites have found diverse applications. However, additive manufacturing and heat treatment of Ti-Al alloys frequently lead to brittleness and severe formation of defects. The present study delves into the interfacial dynamics of these Ti-Al systems, particularly focusing on the behavior of Ti and Al atoms in the presence of TiAl3 grain boundaries under experimental heat treatment conditions. Using a combination of molecular dynamics and Markov state modeling, we scrutinize the kinetic processes involved in the formation of TiAl3. The molecular dynamics simulation indicates that at the early stage of heat treatment, the predominating process is the diffusion of Al atoms toward the Ti surface through the TiAl3 grain boundaries. Markov state modeling identifies three distinct dynamic states of Al atoms within the Ti/Al mixture that forms during the process, each exhibiting a unique spatial distribution. Using transition time scales as a qualitative measure of the rapidness of the dynamics, it is observed that the Al dynamics is significantly less rapid near the Ti surface compared to the Al surface. Put together, the results offer a comprehensive understanding of the interfacial dynamics and reveal a three-stage diffusion mechanism. The process initiates with the premelting of Al, proceeds with the prevalent diffusion of Al atoms toward the Ti surface, and eventually ceases as the Ti concentration within the mixture progressively increases. The insights gained from this study could contribute significantly to the control and optimization of manufacturing processes for these high-performing Ti-Al-based materials.

Simultaneously enhancing strength and ductility of high-Nb-containing TiAl alloy via extrusion-assisted microstructure tailoring

In most metallic materials, the strength-ductility trade-off serves as an inevitable scenario. Therefore, improving the room/high-temperature strength/ductility of high Nb-TiAl alloys based on a lamellar microstructure is important for practical applications. In this work, a novel microstructure with fine lamellar colonies and a certain number of residual γ grains was developed through hot extrusion in the near α phase region. The results indicated that the lamellar colony size and spacing of the as-cast alloy were significantly refined by hot extrusion. The as-extruded Ti-45Al-8Nb-(W, B, Y) alloy demonstrated a good combination of high strength and ductility. The tensile strength and ductility were 1129 MPa and 2.04% at room temperature (RT), respectively, and 744 MPa and 51.20%, respectively, at 850 °C. A simultaneous improvement in strength and ductility below ductile-brittle transition temperature (DBTT) could be attributed to the abundant deformation twins and their intersections, as well as prominent strain working caused by high-density dislocations in the γ phase. Due to dynamic recrystallization, the ductility was significantly enhanced when stretched over DBTT. This extrusion-assisted microstructure tailoring strategy could be extended to other TiAl systems and may serve as a useful solution for addressing the significant engineering constraints posed by the low RT ductility and poor hot-working capabilities of high Nb-TiAl alloys.

Effect of Silicon on the Heat Resistance of Deposited Alloys of the Ti–Al System

Effect of Silicon on the Heat Resistance of Deposited Alloys of the Ti–Al System

Using the Ti–Al System to Understand Plasticity and Its Connection to Fracture and Fatigue in α Ti Alloys

Using the Ti–Al System to Understand Plasticity and Its Connection to Fracture and Fatigue in α Ti Alloys

An accurate interatomic potential for the TiAlNb ternary alloy developed by deep neural network learning method.

The complex phase diagram and bonding nature of the TiAl system make it difficult to accurately describe its various properties and phases by traditional atomistic force fields. Here, we develop a machine learning interatomic potential with a deep neural network method for the TiAlNb ternary alloy based on a dataset built by first-principles calculations. The training set includes bulk elementary metals and intermetallic structures with slab and amorphous configurations. This potential is validated by comparing bulk properties-including lattice constant and elastic constants, surface energies, vacancy formation energies, and stacking fault energies-with their respective density functional theory values. Moreover, our potential could accurately predict the average formation energy and stacking fault energy of γ-TiAl doped with Nb. The tensile properties of γ-TiAl are simulated by our potential and verified by experiments. These results support the applicability of our potential under more practical conditions.

Using Synchrotron Radiation to Investigate Conditions of α2-Phase Formation in Mechanocomposites of a Ti–Al System

Using Synchrotron Radiation to Investigate Conditions of α2-Phase Formation in Mechanocomposites of a Ti–Al System

Investigation of the conditions for the formation of the α<sub>2</sub>-phase in mechanocomposites of the Ti–Al system by synchrotron radiation methods

Synchrotron studies of the features of the dynamics of phase formation in a mechanically activated 3Ti + Al powder mixture during the implementation of high-temperature synthesis under conditions of volumetric ignition by induction heating are carried out. The effect of the time of preliminary mechanical activation treatment of the initial mixture (1, 3, 7 minutes) on the macrokinetic parameters of synthesis was experimentally investigated.

Coupled nucleation of dual-phase lamellar structure

<p>Although lamellar structures widely exist in materials, the existing nucleation knowledge has failed to describe the nucleation process of lamellae. This is because it involves the simultaneous formation of two different phases whose early-stage nuclei are always anisotropic and ordered. We report here a coupled nucleation of lamellae in a eutectoid TiAl system, demonstrating the coupled formation of a pair of anisotropic and ordered ��<sub>2</sub> + �� lamellae from the matrix, and each pair nucleates independently and heterogeneously. The coupled pair has been identified by alternative segregation of Nb in the interface using atom probe tomography. The nucleation kinetics have been confirmed by atomistic simulations and in situ high-energy synchrotron X-ray diffraction. A theoretical model has been proposed for this heterogeneously coupled nucleation, offering potential applications in various systems or phase transitions involving anisotropic, ordered, or lamellar structures. This coupled nucleation model represents a significant enhancement to the existing nucleation theory.</p>

Influence of Dy and Ho on the Phase Composition of the Ti-Al System Obtained by 'Hydride Technology'.

The manuscript describes the phase composition, microstructure, some physical and mechanical properties of the Ti-Al system with addition of 2 at. % Dy (TAD) and Ho (TAH) obtained by "hydride technology". Phase diagrams for Ti-Al-Dy and Ti-Al-Ho at a temperature of 1150 °C and basic properties for ternary phases Dy₆Ti₄Al₄₃ and Ho₆Ti₄Al₄₃ were calculated. A crystallographic database of stable and quasistable structures of the known elemental composition was created in the USPEX-SIESTA software by means of an evolutionary code. The calculations show that adding REM leads to a significant stabilizing effect in each Ti-Al-Me (Me = Dy, Ho) system without exception. It has been established that the lattice energies of AlTi3Ho and AlTi3Dy are, respectively, equal to: EAl4Ti12Dy3 = -32,877.825 eV and EAl4Ti12Dy3 = -31,227.561 eV. In the synthesized Ti49Al49Ho2 compound, the main phases include Al-Ti, Al3Ti3 and Al4Ti12Ho3 and the contributions to the theoretical intensity are equal to 44.83, 44.43 and 5.55%, respectively. Ti49Al49Dy2 is dominated by the Al-Ti, Al3Ti3 and Al4Ti12Dy phases, whose contributions are equal to 65.04, 16.88 and 11.2%, respectively. The microhardness of TAD and TAN specimens is 1.61 ± 0.08 and 1.47 ± 0.07 GPa, respectively.

Interfacial formation of intermetallic Ni-Al-Ti systems formed by induction heating

Intermetallic systems of Nickel (Ni), Aluminium (Al), and Titanium (Ti) are candidates for lightweight materials that offer high-temperature resistance. Combustion synthesis has been widely studied to produce intermetallic and coating deposition by exploiting the heat released by the combustion. An underlayer is often used to enhance the adhesion of the coating to the substrate. The interaction of the coating and the underlayer during heating is, therefore, crucial for achieving a good adhesion quality. This work aimed to investigate the microstructure and properties of the interfacial formation across the NiAl coatings and Ti underlayers formed by combustion synthesis. Induction heating was used to initiate the heating and reaction process with heating rates of 46.6, 57.0, and 85.5 K/s. The microstructure was characterized by Scanning Electron Microscopy (SEM) equipped with an Energy Dispersive Spectroscopy (EDS) detector, whereas the formed phases were identified using X-ray Diffraction (XRD) tests. The hardness distribution was measured by the Vickers microhardness test. The result shows that NiAl with Al-rich and Ni-rich were formed in the coating region. The average thickness of the coating increases by approximately 200, 300, and 400 µm with a heating rate of 46.6, 57.0, and 85.5 K/s, respectively. The different thicknesses of the coating can be attributed to the migration of Ni/Al from the coating to the underlayer zones. The microstructure observed in the underlayer confirms the formation of several intermetallic phases of Ni-Ti and Ti-Al systems. The infiltration of Ni and Al elements from Ni and Al to Ti sides was responsible for generating a reaction between Ni-Ai-Ti. The formation of Ti2Ni–Ti3Al phases in the underlayer increases with the heating rate. The hardness across the coating, interface, and underlayer increases with the heating rates. The heating rate of 46.6, 57.0, and 85.5 K/s results in the hardness of the interface by 669.1, 804.8, and 967.7 HV, whereas the underlayer increases by 680.1, 772.7, and 978.7 HV, respectively. The increased content of the Ni-Al-Ti system, which are AlNi2Ti and Ti2Ni–Ti3Al phases, was attributed to the increased hardness of the interface and underlayer. This work improves the understanding of second reactions across the interface while fabricating coatings that apply an underlayer.

Extension of the functionality of the software for MD-simulation of the SH-synthesis of intermetallides in Ni-Al and Ti-Al nanosystems

The subject of research: the methodological and functional capabilities of specialized software packages of free access LAMMPS and OVITO and author's programs used for simulation of SHS-microkinetics in heterogeneous systems.
 Purpose of research: to increase information content, 3D-visualization, and adequate interpretation of the processes of structural-phase transformations at interfaces of the layered, layered-block nanoscale Ni-Al and Ti-Al systems.
 Methods and objects of redearch: the molecular dynamics simulation method implemented in the basis of the LAMMPS software package simulates the process of initiation and propagation of the SHS combustion wave in the systems under study, and using the OVITO package, 3D-visualization of the processes of dissolution, diffusion, and motion of the SHS combustion wave front is carried out.
 Main results of research: it is shown that the development by the author of software modules for calculating one-dimensional temperature and density profiles of the synthesized material along the direction of combustion wave motion, as well as for calculating and visualizing the 3D-structure of the distribution of synthesized intermetallic interlayers at the interface in nanoparticles with the Ni-Al "core-shell" structure (and similarly for Ti-Al) allows, in contrast to the OVITO package, to detect heterophase intermetallic structures in such systems. As a result of a large series of computational experiments on simulation of microkinetics in the studied nanoscale Ni-Al and Ti-Al systems, it has been established that the software package created by the author with support for parallel computing, which, in addition to the licensed packages LAMMPS and OVITO, integrates author's software modules, has new broader functionality in the methodological aspect of the study of the problems of physical chemistry of the SHS process and is a vivid example of the created software engineering tools in this area of research.

CAVITATION AND EROSION RESISTANCE OF VACUUM ARC Ti, Ti-Al, Ti-Zr, AND Ti-Ni COATINGS

Studies on the influence of technological parameters (cathode-substrate distance, substrate temperature, bias voltage, arc current) of vacuum-arc titanium deposition coatings have shown that the deposition rate from one cathode is inversely proportional to the square of the distance between the sample and the cathode surface and proportional to the angle of inclination of the sample relative to the normal to the cathode surface. Sputtered titanium coatings at optimal parameters have 1.25 times higher cavitation resistance than bulk titanium. Among the alloyed vacuum-arc coatings TiAl, TiZr, and TiNi, coatings of the TiAl and TiNi systems have the highest resistance to cavitation and abrasive wear.