Titanium Trialuminide Research Articles

Ti-Al3Ti metal-intermetallic laminate (MIL) composite with a cubic titanium trialuminide stabilized with silver: Selection of fabrication regimes, structure, and properties

Ti-Al 3 Ti metal-intermetallic laminate (MIL) composites are known as promising structural materials due to the unique combination of their specific properties. However, their application is still limited due to the extremely high brittleness of the Al 3 Ti phase. In this study, we attempt to address this issue by changing the D0 22 crystal structure of Al 3 Ti to the more ductile L1 2 structure by alloying it with silver. To select the best fabrication regimes of Ti-Ti(Al 1−x Ag x ) 3 composites, in situ synchrotron X-ray diffraction analysis was performed to reveal the chemical reactions occurring upon heating the Ti-Al-Ag sample. The analysis showed that the highest amount of Ti(Al 1−x Ag x ) 3 phase with the L1 2 structure appears at 930 °C. This temperature was chosen for subsequent spark plasma sintering experiments. Scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction analysis revealed that the sintered sample consisted mainly of Ti, Ti(Al 1−x Ag x ) 3 , and a minor fraction of the Ag-Al compound distributed in the central parts of the intermetallic layers and at the grain boundaries. Modification of the titanium trialuminide crystal structure positively affected the properties of the composite, providing a 60% increase in fracture toughness. The Ag-Al phase also contributed to toughening, causing an additional crack deflection effect. • Ag stabilizes L1 2 crystal structure of Al 3 Ti in Ti-Al 3 Ti multilayer composite. • The maximum fraction of L1 2 phase in the composite is reached at 930 °C. • Modification of the Al 3 Ti provides 60% increase of the composite fracture toughness. • Minor Al-Ag phase causes the additional crack deflection effect.

On the texture and superstructure formation in Ti–TiAl3–Al MIL composites

In recent decades, metal-intermetallic laminated (MIL) composites are of great interest to the scientific community. The intermetallic layers in such composites possess a strong crystallographic texture and can form various superstructures. However, these effects are rarely discussed in the literature. By application of synchrotron X-ray diffraction (SXRD) we show, that an intermetallic layer in explosively welded and annealed Ti–Al-based MIL composite consists of two modifications of titanium trialuminide: TiAl3 with a D022 structure and its superstructure Ti8Al24. According to SXRD analysis, the volume fraction of the Ti8Al24 modification increases from Al/intermetallic interface towards Ti/intermetallic interface. This may be caused by the lack of Al for the formation of stoichiometric titanium trialuminide near the interface with Ti, which leads to the formation of a long-period structures having Ti1+xAl3-x stoichiometry. Two types of fiber texture were formed in the titanium trialuminide layer: [001] near the Ti/intermetallic interface and <100> near the Al/intermetallic interface, which is caused by peculiarities of Ti and Al atoms migration. To explain the features of the forming texture, hypothetical mechanisms of Al and Ti diffusion in the intermetallic layer are discussed in this study: a vacancy diffusion, an interstitial diffusion, and a six jump vacancy cycle (6JVC).

In situ synchrotron X-ray diffraction study of reaction routes in Ti-Al3Ti-based composites: The effect of transition metals on L12 structure stabilization

In the last few decades, Ti-Al3Ti composites have attracted great attention due to their outstanding mechanical characteristics, such as low density, high specific strength and stiffness, and ballistic properties. However, their application is still limited due to the low ductility and fracture toughness of the Al3Ti phase. A promising way to improve the composite’s properties is to transform the Al3Ti crystal structure from the tetragonal D022 type to the cubic L12 type. In this study, the stabilization of the L12 structure of titanium trialuminide during the fabrication of the Ti-Al3Ti composite is discussed. For this reason, the method of in situ synchrotron X-ray diffraction analysis was used to observe the reactions in the ternary Ti-Al-M systems (where M is Zn, Au, Ag, Ni, Pd, Pt, Mn, Fe, Co or Cr) during heating from room temperature to 830 °С. Zn and Ag were found to be the most efficient stabilizers of the L12 structure. In composites alloyed with Fe, Co, and Cr, the L12 structure of Al3Ti was not stabilized. Formation of L12-structured titanium trialuminide in the remaining systems was accompanied by the formation of a large number of co-products. To select the elements stabilizing L12 structure in the composite with an excess amount of Ti, the following principle was formulated: the preferable stabilizers are the elements with FCC and HCP structures and a melting temperature below 1100 °С, and which do not form refractory Al-rich binary compounds with a melting point above 1000 °С.

Effect of Ultrasonic Cavitation and Chemical Erosion on TC4 Titanium Alloy in Aluminum Melt

Abstract An ultrasonic radiation rod made of Ti-6Al-4V (TC4) titanium alloy can be eroded in an aluminum alloy casting, which can also affect the stable transmission of ultrasonic waves. This erosion is a result of complex, multifactor interaction. Therefore, two groups of experiments were designed: one group did not apply ultrasonic treatment (UST), while the other group did. Five titanium alloy samples removed from the radiation rod were ground on the automatic grinding machine to make their surface roughness similar. The four samples were placed in the molten aluminum for 4.5, 9, 13.5, and 18 h, respectively, without UST. The remaining sample was placed in molten aluminum with UST for 4.5 h. The four samples without UST were cooled and cut through the middle position by a wire-cutting machine. The cross sections of the four samples were ground and observed by a scanning electron microscope (SEM). The generated chemical layer was determined to be titanium trialuminide alloy (TiAl3) by energy dispersion spectrum (EDS) analysis, and its thickness was approximately 20–50, 145, 220, and 345 μm, respectively, corresponding to different processing times. The fifth titanium alloy sample was processed by UST, the residual aluminum on the sample surface was removed by hydrochloric acid, and obvious erosion pits and microcracks were found by SEM. The roughness of the surface was approximately 340 μm in the LY-WN-YH 3-D system. Therefore, the effect of ultrasonic cavitation on TC4 titanium alloy is much larger than that of a chemical reaction.

Formation sequence of intermetallics and kinetics of reaction layer growth during solid state reaction between titanium and aluminum

Understanding on the reaction kinetics associated with the formation of intermetallic compounds and the mechanisms involved in evolution of the reaction product at different temperatures due to solid state reaction in Friction Stir Welding (FSW) of dissimilar materials is very important in selecting optimum operating condition to control intermetallic compounds for safety-critical applications. In this study, the evolution sequence of intermetallic compounds and reaction kinetics during the solid state reaction between Ti and Al has been investigated. It was found that the mechanical mixing of Al and Ti affects evolution of reaction layers (RL) and intermetallic compounds. The thickness of the RL increases with reaction temperature and titanium trialuminide (Al3Ti) was found to be the only ordered phase that is formed at a higher temperature (650 °C). The activation energy for the growth of the reaction layer was found to be significantly lower when compared to conventional welding. The sequence of formation of these intermetallic compounds is proposed based on kinetics and thermodynamic principles such as inter-diffusion and free energy of formation. The variation in stoichiometry at the Al/Ti interfaces due to mechanical mixing as occurred during FSW and difference in diffusivity of Al and Ti through reaction layers are considered responsible for the phase evolution and growth of these layers. The mechanism of the reaction with the reduced activation energy was attributed to fragmentation, mechanical mixing, development of dislocation and twinning in materials, activation of atoms due to severe deformation and grain boundary diffusion.

Formation Sequence of Intermetallics and Kinetics of Reaction Layer Growth During Solid State Reaction between Titanium and Aluminum

Understanding on the reaction kinetics associated with the formation of intermetallic compounds and the mechanisms involved in evolution of the reaction product at different temperatures after Friction Stir Welding (FSW) of dissimilar materials is very important in selecting optimum operating condition to control intermetallic compounds for safety-critical applications. In this study, the evolution sequence of intermetallic compounds and reaction kinetics during the solid state reaction between Ti and Al following FSW has been investigated. It was found that the mechanical mixing of Al and Ti that occurs in FSW affects evolution of reaction layers (RL) and intermetallic compounds. The thickness of the RL increases with reaction temperature and titanium trialuminide (Al3Ti) was found to be the only ordered phase that is formed at a higher temperature (650 °C). The activation energy for the growth of the reaction layer was found to be significantly lower when compared to conventional welding. The sequence of formation of these intermetallic compounds is proposed based on kinetics and thermodynamic principles such as inter-diffusion and free energy of formation. The variation in stoichiometry at the Al/Ti interfaces due to mechanical mixing as occurred during FSW and difference in diffusivity of Al and Ti through reaction layers are considered responsible for the phase evolution and growth of these layers. The mechanism of the reaction with the reduced activation energy was attributed to fragmentation, mechanical mixing, development of dislocation and twinning in materials, activation of atoms due to severe deformation and grain boundary diffusion.

Ballistic limit velocity of tungsten alloy spherical fragment penetrating Ti/Al3Ti-laminated composite target plates

To determine the ballistic limit velocity of titanium–titanium tri-aluminide (Ti/Al3Ti)-laminated composites under the action of tungsten alloy spherical fragments, a type of 12.7 mm ballistic gun loading system was used to test the tungsten alloy spherical fragments vertically impacting the Ti/Al3Ti-laminated composite targets with different thickness. The relationship between the ballistic limit velocity and the target area density of the Ti/Al3Ti-laminated composite was obtained. As the area density increased, the ballistic limit velocity and the ballistic energy absorbed by the target plate also enhanced. Based on the dimensional analysis and similarity theory, a simulation law of tungsten alloy spherical fragments penetrating Ti/Al3Ti-laminated composite targets with different thickness was studied and an empirical formula for the ballistic limit velocity was obtained. The research results had an important application value for the optimal design of the light armor protection structure.

Effect of shape-memory alloy NiTi fiber on microstructure and mechanical properties of continuous ceramic Al2O3 fiber-reinforced Ti/Al3Ti metal–intermetallic laminated composite

Shape-memory alloy titanium nickel (NiTi) fiber was introduced into continuous ceramic aluminum oxide (Al2O3) fiber-reinforced titanium–titanium trialuminide metal–intermetallic laminated (CSMAFR-MIL) composite using vacuum hot pressing (HP) sintering method to improve the microstructure and mechanical properties of the composite. Scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction techniques were employed to characterize the microstructure of the novel CSMAFR-MIL composite. Besides, the tensile tests were carried out on continuous Al2O3 fiber-reinforced Ti-Al metal–intermetallic laminated (CFR-MIL) composite and the CSMAFR-MIL composite to explore the influence of NiTi fiber additive on mechanical behavior of the CFR-MIL composite. The experimental results showed that the intermetallic layer including Al3Ti, Al3Ti0.8V0.2, Al3Ni intermetallics but without residual NiTi fiber was generated via the reactions of liquid Al with NiTi fiber and Ti foil during preparation. Moreover, owing to the addition of NiTi fiber, intermetallic centerline was prevented effectively to form in the CSMAFR-MIL composite. Moreover, the elemental diffusion occurred between the Al2O3 fiber and the intermetallic, revealing that the metallurgical bonding was formed during the fabrication process. Furthermore, the CSMAFR-MIL composite possessed higher strength and superior ductility than those of CFR-MIL composite attributed to the microstructure optimization.

The production and properties of Al3Ti reinforced functionally graded aluminum matrix composites produced by the centrifugal casting method

In this study, the production and properties of titanium tri-aluminide (Al3Ti) particle reinforced functionally graded composites (FGCs) by a centrifugal casting method, are investigated. FGCs were produced by using Al-Ti master alloy which was alloyed with copper and silicon and without alloying to obtain three types of composites, namely Al3Ti/Al, Al3Ti/Al-Si and Al3Ti/Al-Cu FGC. It was observed that produced composites contain two different area: the functionally graded and Al3Ti-free area. The ratio and size of Al3Ti particles were found to change regionally in functionally graded area of each composite type. The effects of the regional change in functionally graded area and both the reinforcement ratio and particle size of composite types were discussed using statistical techniques. In addition, density, Brinell hardness and abrasive wear property of Al3Ti particle reinforced FGCs have been examined inwardly from the outer surface of composites depending on the centrifugal force direction. The results showed an improvement in Brinell hardness value inwardly from the outer surface of composites in each composite type. It was observed that the volumetric wear loss of composites were reduced by increasing the ratio of Al3Ti particles in the matrix.

Influence of Nb and Cu Elements on the Intermetallic Particles Morphology in Ti/Al Multilayer Composite Processed Through Hot Pressing and Rolling

Ti–Al–Nb composites were produced by solid state diffusion bonding through hot pressing and rolling followed by annealing at 700 °C for 0.5, 1, 1.5 and 2 h. The morphologies of TiAl3 intermetallics were investigated by Scanning Electron Microscopy combined with Energy-dispersive X-ray spectroscopy. Titanium tri-aluminide (TiAl3) particles with blocky morphology were dispersed into Aluminum matrix. In the presence of niobium and copper, TiAl3 particles were produced in different sizes and morphologies. The presence of Nb in the composite led to the formation of irregular angular morphology, while the copper resulted in cubic morphology of the intermetallic particles. The EDS results indicated that TiAl3, (Ti, Nb)Al3 and (Ti, Nb, Cu)Al3 intermetallic compounds appeared near Ti zone, Nb Zone and in the presence of Cu, respectively.

High Temperature Deformation Behavior of L12 Modified Titanium Trialuminides Doped with Chromium and Copper

Crystal structure of the L12 type (Al,X)3Ti alloy (X = Cr,Cu) is analyzed by X-ray diffractometry and the nonuniform strain behavior at high temperature is investigated. The lattice constants for the L12 type (Al,X)3Ti alloys decrease in the order of the atomic number of the substituted atom X, and the hardness tends to increase. In a compressive test at around 473K for Al67.5Ti25Cr7.5, Al65Ti25Cr10 and Al62.5Ti25Cu12.5 alloys, it is found that the stress-strain curves showed serration, and deformation rate dependence appeared. It is assumed that the generation of serration is due to dynamic strain aging caused by the diffusion of solute atoms. As a result, activation energy of 60-95 kJ/mol is obtained. This process does not require direct involvement. In order to investigate the generation of serrations in detail, compression tests are carried out under various conditions. As a result, in the strain rate range of this experiment, serration is found to occur after 470K at a certain critical strain. The critical strain increases as the strain rate increases at constant temperature, and the critical strain tends to decrease as temperature rises under constant strain rate. This tendency is common to all alloys produced. In the case of this alloy system, the serration at around 473K corresponds to the case in which the dislocation velocity is faster than the diffusion rate of interstitial solute atoms at low temperature.

Synthesis of metal-intermetallic laminate (MIL) composites with modified Al3Ti structure and in situ synchrotron X-ray diffraction analysis of sintering process

Al3Ti-based alloys attract exceptional attention due to their high specific mechanical properties. However, their application is still insufficient due to their low ductility and fracture toughness. Several approaches were previously proposed to address these problems. The first one is stabilization of the cubic modification of titanium trialuminide by alloying. Another approach consists in fabricating metal-intermetallic laminated composites (MIL). In this study, we combined both methods to synthesize the first MIL composite with cubic Al3Ti interlayers. Copper additions were used to stabilize the cubic modification of Al3Ti and produce a novel Ti-Al5CuTi2 MIL composite. First mechanical characterization by indentation tests showed that the binary Al3Ti intermetallic tended to crack at a load of 0.2 kg while the fracture was not observed in the Al5CuTi2 layers at least at a load of 1 kg. These results are an indirect evidence of a higher ductility and fracture toughness of the composite with cubic Al3Ti compared to tetragonal one. The sequence of the phase transformations in the Al-Ti-Cu system was studied using in situ synchrotron X-ray radiation diffraction. The formation of Al5CuTi2 occurred via several intermediate stages including eutectic melting of Al and Cu and the formation of binary AlCu and Al3Ti compounds.

Mechanical response of titanium tri-aluminide intermetallic alloy

The bulk titanium tri-aluminide intermetallic alloy was fabricated via foil reactive sintering using Ti and Al foils in the vacuum. Scanning electron microscopy (SEM) results demonstrated that the original Ti and Al foils were fully reacted and the only synthesized product is monolithic intermetallic Al3Ti. The basic physical properties of the fabricated intermetallic, such as Young's modulus and Poisson ratio, were determined using an ultrasonic wave measurement technique, and the compressive mechanical responses under both quasi-static and high strain rates were studied using universal load frame and modified split Hopkinson pressure bar system, respectively. The experimental results indicated that intermetallic Al3Ti exhibits brittle features, and its compressive strength was sensitive to strain rate. Moreover, the strain rate hardening behavior under high rate range is stronger than that under quasi-static deformation conditions.

Theoretical investigations on phase stability, elastic constants and electronic structures of D022- and L12-Al3Ti under high pressure

Phase stability, elastic and thermodynamic properties, and electronic structure of titanium trialuminide (Al3Ti) with Ll2 and D022 structures under pressure up to 40GPa have been investigated using first-principles calculations. The equilibrium structure and formation energy show that L12-Al3Ti is stable when the pressure is higher enough, approximately above than 20–30GPa. The elastic constants, anisotropy index and Debye temperature of both phases increase with the pressure going up, and L12-Al3Ti has better ductility, smaller anisotropy and lower Debye temperature than D022-A13Ti. The pressure-induced Ti-3d delocalization can strengthen its orbital hybridization with Al(s,p), which leads to stronger atomic bonding, and subsequently makes the L12-Al3Ti more stable under high pressure.

In-situ synthesis of Al3Ti particles reinforced Al-based composite coating

Using titanium wires (99.5%, 200 μm in diameter) as a reactive source, an Al-based composite coating reinforced by titanium tri-aluminide (Al3Ti) particles was fabricated by infiltration plus in-situ methods. According to the differential thermal analysis (DTA) curve, the reactive temperature between Ti wires and Al matrix can be determined at 890 °C. The obtained composite coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microhardness and wear test. The experimental results show that when holding period is 20 min at 890 °C, the titanium wires react completely to in-situ synthesize Al3Ti particles, which presents blocky and strip-like states. The microhardness of in-situ synthesized Al3Ti particles is about 4.5 times that of the Al-matrix. Under the condition of dry sliding at 10 N load, compared with the unreinforced Al matrix, the composite coating fabricated with 20 min offers unique wear resistance behavior, and its wear mechanism is that the adhesive wear and abrasive wear coexist.

Preparation of &lt;i&gt;In Situ&lt;/i&gt; Al&lt;sub&gt;3&lt;/sub&gt;TiP/Al-Based Composite Coating

In the paper, titanium tri-aluminide (Al3Ti) particles reinforced aluminium (Al)-based composite coatings were fabricated by infiltration plus in-situ techniques at 891.3 °C. The obtained composite coatings are characterized by XRD, SEM and friction and wear testers. The experimental results show that the reaction between Ti wires and Al molten increases with extending time, Ti wires can totally transform into Al3Ti particles for 20 min, which present blocky and strip-like states, respectively. The wear rates of the composite coatings decrease with increasing time.

Influence of Sintering Temperature on the Microstructure of TiB&lt;sub&gt;2&lt;/sub&gt; Sintered with Al&lt;sub&gt;3&lt;/sub&gt;Ti Additive

Titanium diboride (TiB2) has been sintered using spark plasma sintering (SPS) with the addition of titanium tri-aluminide (Al3Ti) at the temperature between 1273 and 1573K. By the X-ray diffraction measurements, it has been shown that TiB2­Al3Ti composites can be obtained by the sintering at 1273K. Vickers hardness of the specimen increases as the amount of Al3Ti increases up to 30% by the sintering at 1273K, and TiB2­30mass% Al3Ti composite has the relative density of around 96% and Vickers hardness as high as 2100Hv. On the other hand, Al3Ti evaporates during sintering above 1473K. TiB2 sintered with 10mass% Al3Ti at 1573K has the relative density of 94% and Vickers hardness 2100Hv, while TiB2 sintered without Al3Ti has the relative density as low as 76%. This fact indicates that Al3Ti accelerates the diffusion of TiB2 causing densification of sintered TiB2 specimens in the sintering above 1473K. [doi:10.2320/matertrans.M2012113]

Micro structural features and mechanical properties of Al–Al 3Ti composite fabricated by in-situ powder metallurgy route

In this paper, an in-situ powder metallurgy technique of fabricating near net shape particulate Al 3Ti–Al composite is developed. Titanium tri-aluminide particles were generated in aluminum matrix by solid state reactive diffusion of homogenous blended pure Ti and Al powders. Effects of titanium particle size, temperature and time of sintering on microstructure and mechanical properties of the composite were studied by X-ray diffraction analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy and tensile testing. After 5 h sintering at 600 °C, Al 3Ti intermetallic particles were formed as the major second phase. By decreasing the titanium particle size or increasing the sintering time, the amount of Al 3Ti phase increased. Tensile strength of the composite was affected significantly by the amount of porosity and intermetallic phase as two dominant factors. By decreasing the amount of porosity or the average particle size of Ti powder, a significant increase in tensile strength was observed.

Formation of Al3Ti/Mg composite by powder metallurgy of Mg–Al–Ti system

An in situ titanium trialuminide (Al3Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg–Al–Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al3Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg–Al–Ti system, Al3Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg–Al–Ti system is almost the same as that of the Al–Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix.

A new-developed magnesium matrix composite by reactive sintering

Abstract The present work was undertaken to highlight a novel magnesium matrix composite. Thermodynamics analysis by Miedema model predicts that Al–Ti intermetallics are the predominant equilibrium phases of Mg–Al–Ti system. An in situ titanium tri-aluminide (Al3Ti) particulate reinforced magnesium matrix composite has been fabricated successfully through reactive sintering of Mg–Al–Ti system. The composite is characterized by a relatively homogeneous distribution of Al3Ti particulates with a size range of 2–4 μm and a good cohesion at the matrix/particulate interface. The hardness, compressive ultimate stress and wear resistance of the Al3TiP/Mg composite are evidently increased, compared with pure magnesium and AZ31 magnesium alloy.