Al3Ti Particles Research Articles

Research on Microstructure and Refining Performance of Al-Ti-C Grain Refiner Prepared by Ultrasonic Coupling

The application of ultrasonic field in the preparation of Al-Ti-C refiners can lead to the the homogenous distribution of the second phase TiAl3 and the particle phase TiC in the matrix, thus enhancing the refinement effect. In this paper, the Al-Ti-C grain refiner was successfully prepared by the ultrasonic coupling method, and its microstructure was observed. The prepared refiner was added to pure Al to verify the refining performance, and the refining mechanism was analyzed. The results indicate that the Al-Ti-C grain refiner prepared by ultrasonic field has excellent refining performance, which reduces the grain size of Al to 100 μm, and the optimum activation refining time is 3 min. The reason is that the morphology and size of the second phase TiAl3 and TiC in Al-Ti-C are changed by cavitation effect, acoustic streaming effect and thermal effect caused by high intensity ultrasonic, and the α-Al nucleates effectively under the synergistic of TiC and TiAl3 particles.

Interaction between nucleant particles and a solid-liquid interface in Al-4.5Cu alloy

Al3Ti and TiB2 particles were made in-situ from adding halide salts in molten Al-4.5 wt % Cu alloys. The molten halide salts also dissolved the oxide in the molten metal to ensure that the newly formed Al3Ti and TiB2 particles had intimate interfaces with the molten metal. Excess amounts of titanium were added into the melt to ensure that the wetting angles between the particles and the molten alloy were small and the particles were able to significantly reduce the grain sizes of the aluminum alloy. Such particle/matrix systems should have a negative total interfacial energy change when a particle is engulfed into the solid by an advancing solid-liquid interface, resulting in particles being engulfed by an advancing solid-liquid interface according to widely accepted theories on particle pushing. Experimental results indicate that these particles are actually pushed by the growing dendrites into the interdendritic regions, regardless of the growth rates being positive, close to nil, or even negative. It seems that the particle pushing mechanisms based on interfacial energy interactions are not applicable for these particle/matrix systems under experimental conditions of this study. Analytical analysis suggests that these particles are pushed by the growing dendrites due to fluid flow before they could get into close contact with the solid-liquid interface within a several interatomic layers where the van der Waals forces become significant. The shrinkage driven flow in the liquid of the mushy zone is sufficient to dislodge a particle from a depression and rolls the particle on the solid-liquid interface.

Electrical Explosion Synthesis, Oxidation and Sintering Behavior of Ti-Al Intermetallide Powders

In this research, Ti-Al powders were produced by electrical explosion of twisted titanium and aluminum wires. The resulting powders were pressed and sintered in a vacuum to obtain bulk composites. Transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) studies were performed to analyze synthesized powders and bulk composites. The studies carried out showed the presence of α-Ti, α2-Ti3Al, and γ-TiAl phases, which are formed by coalescence of Ti and Al clusters formed in the process of non-synchronous electrical explosion of twisted wires. Furthermore, an increase in the energy injected into the wires leads to a decrease in the content of micron particles in the powder. During sintering of pressed Ti-Al powder in the range 800–1250 °C, phase transformations occur due to the diffusion of aluminum atoms towards Ti compounds. The research findings can be used to obtain Ti-Al particles and bulk composites with a controllable phase composition.

Effect of Gd on microstructure and refinement performance of Al-5Ti-B alloy

Al-5Ti-B and Al-5Ti-B-Gd master alloy refiners were fabricated by fluorine salt casting method. The microstructure and phase constitution of the master alloys were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Al-Ti-B alloy refiner consists of Al3Ti phase and TiB2 phase. After Gd is introduced into the intermediate alloy, Ti2Al20Gd phase appears in the alloy, the size of Al3Ti is significantly reduced, and Ti-Al-Gd phase is found in the edge of Al3Ti phase. At the same time, some independent Ti-Al-Gd phases appear in local areas, which are Ti2Al20Gd phase determined by micro-area electron diffraction analysis. Analysis and calculation results of the high-resolution images of the Ti2Al20Gd/Al structure show that there is no other compound at the junction between the Ti2Al20Gd phase and Al, and Ti2Al20Gd phase has a great difference in atomic space with the α-Al, which cannot be directly used as heterogeneous nucleus. But, after being decomposed in the aluminum melt, the Ti2Al20Gd phase can promote the refinement effect of the refiner. In the Al-Ti-B-Gd master alloy, there are many dispersed Al3Ti particles with a size of less than 1 µm, which can promote the Al-5Ti-B refining effect.

HVAF deposition mechanism of γ-TiAl-based coating containing β phase

The Ti-45Al-7Nb-4V, Ti-45Al-7Nb-4Cr, Ti-45Al-7Nb-2V-2Cr alloy coatings were prepared on the surface of the aluminum alloy by high-velocity-air-fuel (HVAF). The surface and cross-section of three kinds of titanium aluminum alloy coatings and the micromorphology of the bonding interface between the coating and substrate were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The deformation behavior of titanium aluminum alloy particles and the phase composition of the titanium aluminum alloy coating were analyzed by X-Ray Diffraction (XRD) and energy dispersive x-ray analysis (EDAX). The results show that the coordinated deformation between TiAl particles and Al alloy matrix is a necessary condition for the deposition of the first layer of titanium‑aluminum alloy particles. The bonding mechanism of the TiAl coating and the matrix is mechanical bonding, and there are both mechanical bonding and metallurgical bonding between spraying particles. In the process of coating deposition and formation, the β phase grains undergo coordinated deformation to form typical structures such as striped grains and circular columnar crystals. The deformation mechanism of the titanium aluminum alloy particles is the slip and kink mechanism in the grains, and the sliding and rotation mechanism of the grain boundary and the phase boundary. Adiabatic shear instability and dynamic recrystallization occurred during the formation of titanium aluminum alloy coating.

Melting temperature of Ti and TiAl nanoparticles in vacuum and in Al matrix depending on their diameter: molecular dynamics study

The dependence of the melting temperature of Ti and TiAl nanoparticles on their diameter in vacuum and in Al matrix was studied by the method of molecular dynamics using EAM potentials of Zope and Mishin. Particles with a diameter of 2.5 to 12 nm were considered. The obtained values of the melting point are in good agreement with the approximation curves constructed on the basis that the decrease in the melting temperature is proportional to the ratio of the surface area of the particle to its volume. Wherein the values of the melting temperature of Ti and TiAl particles in the aluminum matrix turned out to be lower than those of particles in vacuum, which is explained by the smearing and disordering of the interface due to mutual diffusion. As the size of particles in vacuum and in aluminum increased, the values of their melting points tended to the same value, which is explained by the decrease in the role of the diffusion-blurred interface with an increase in the particle diameter. The particles began to melt from the surface. The velocity of movement of the melting front depended on temperature and increased with increasing temperature. In the case of particles in aluminum matrix, at temperatures close to the particle melting point, mutual diffusion was significantly accelerated due to melting of the particle boundary layer. Al atoms penetrating into the particle accelerated the movement of the melting front, rapidly occupying the next destroyed layer of the particle.

The Influence of Porosity on the Statistical Amplitude Distribution of Backscattered Ultrasonic Pulses in Reactive Cast Metal–Matrix Composites

In this work, we study the influence of the local porosity in isotropic reactive cast particulate reinforced metal–matrix composites on the statistical amplitude distribution of backscattered broadband pulses of longitudinal ultrasonic waves. A special laser optoacoustic transducer is employed for this purpose, which makes it possible to achieve laser excitation and piezoelectric detection of ultrasound by one-side access to a sample or product. Two series of in-situ reactive cast aluminum–matrix composites were studied: reinforced solely with the Al3Ti intermetallic particles (volumetric contents 0.04–0.115) and with combination of Al3Ti and synthetic diamond nanoparticles (volumetric content 0.002). The last accelerate reactive synthesis of Al3Ti particles and lead to modification of their shape and sizes. For both series of composites, the amplitude distribution of backscattered ultrasonic pulses has been approximated with the Gaussian probability distribution applicable for statistics of large number of independent random variables. The empirical dependence of the half-width of this distribution on the local porosity in composites of two series has been fitted by the same function close to the linear one regardless the size and content of reinforcing particles. This functional relationship can be used for quantitative evaluation of the local porosity of the composite material both at its manufacturing stage and during service of composite parts and products.

Effects of modifying the hypoeutectic AlMg5Si2Mn alloy via addition of Al10Sr and/or Al5TiB

This work demonstrates that the combined addition of Al10Sr and Al5TiB master alloys to the AlMg5Si2Mn effectively refines the grain microstructure and partially modifies the eutectic Mg2Si phase. Thorough spectroscopic characterization reveals that the grain refinement effect is due to Al3Ti particles acting as nucleation sites for α-Al grains, and the increased nucleation temperature of α-Al is due to Al10Sr addition. It is also determined that TiB2 particles can act as nucleation substrates for the primary Mg2Si phase. The prepared alloy sample with the finest microstructure (treated with both Al10Sr and Al5TiB) exhibits the greatest corrosion resistance among all tested samples.

Changes in the spatial distributions of platelet Al3Ti particles in an Al-Al3Ti alloy by equal-channel angular pressing

Changes in the spatial distributions of platelet Al3Ti particles in an Al-Al3Ti alloy during equal-channel angular pressing (ECAP) were investigated. ECAP was performed under the processing routes of A and Bc up to 8 passes through a die. When applying route A, the Al3Ti particles were greatly fragmented during the ECAP process and also aligned along to the deformation axis, while route Bc resulted in the agglomeration of the Al3Ti particles. The Al3Ti particle size was also found to gradually decrease as the number of ECAP passes was increased. The spatial distributions of these Al3Ti particles in specimens deformed by ECAP were evaluated using the Morisita index, and the results showed that both processing routes generated aggregate distributions, although route Bc produced a homogeneous distribution of Al3Ti particles after 8 passes. These variations in the spatial distributions of the Al3Ti particles can be explained by the occurrence of material flow of the α-Al matrix during ECAP using routes A and Bc.

Grain refinement of commercially pure aluminum with addition of Ti and Zr elements based on crystallography orientation

The edge-to-edge matching (E2EM) model and electron back-scatter diffraction (EBSD) technique are used to explore the grain refinement mechanism of commercially pure Al through the addition of Ti and Zr elements. EBSD results show that there are favorable crystallography orientation relationships (ORs) between both Al3Ti and Al3Zr particles with α-Al matrix. Due to these ORs Al3Ti and Al3Zr particles act as the heterogeneous nucleation site during solidification nucleation of Al–Ti and Al–Zr alloys, respectively. Furthermore, both Al3Ti and Al3Zr particles have small values of interplanar spacing mismatch and interatomic spacing misfit with respect to α-Al matrix by using E2EM. It shows that micro-addition of Ti and Zr element is efficient heterogeneous nucleation refiner in commercial purity Al or Al alloys. Besides, there may be some other mechanisms in grain refinement of Al alloys with addition of Ti grain refiner.

Formation and wear behaviors of in-situ Al3Ti/Al composites using aluminum and titanium fibers under electromagnetic induction heating

Under various electromagnetic induction heating powers, different Al3Ti/Al composites were fabricated by in-situ synthesis method from aluminum and titanium fibers. Microstructures and particles distribution of the composites were examined by XRD, SEM and EDS. The results show that no other intermetallic compounds beside Al3Ti can be in-situ synthesized. Around the titanium fibers, the reaction zones and diffusion zones can be obviously found. Due to the stirring of the electromagnetic function, the formation of the micro-cracks inside the reaction zone was conducive to the peeling off of the Al3Ti particles, and ensures the continuous reaction between liquid aluminum and titanium fibers, as well as the diffusion of Al3Ti particles. At the same time, there were secondary splits of Al3Ti particles located in diffusion zones. Two-body abrasion test shows that with the increase of induction heating power, the wear rates of the composites reduced and the number of grooves decreased.

Investigation of the grain refining performance of Al‐5Ti‐1B master alloy on the recycling process of A356 alloy

AbstractIn this paper, the grain refining performance of Al‐5Ti‐1B master alloy on the recycled A356 alloy is investigated using the macrostructure examination and chemical analysis. Results show that Al‐5Ti‐1B is composed of the dispersion of blocky TiAl3 particles and mixtures of small TiAl3 and TiB2 particles. Both particles refine grain structures of A356 alloy. As the initial recycling process proceeds, A356 alloy still exhibits fine structures. However, during the subsequent recycling process, the grain size of A356 alloy become larger. The concentration of titanium and boron decreases with increasing the number of recycling, especially in the subsequent recycling process. It is proposed that recycling of refined A356 can best be conducted in the initial recycling process and then additional grain refiner needs to be added to maintain the grain refining performance for the continuous recycling process of A356 alloy.

The elastic constants measurements in a TI-6AL-4V eli alloy by ultrasound

In this paper, we report the calculation of the elastic constants such Poisson's ratio, elastic modulus and shear modulus deduced from the ultrasonic propagating equations with two types of ultrasonic vibrations named longitudinal and transverse waves. The ultrasonic propagating velocity is measured at the microstructural evolution in a Ti-6Al-4V medical alloy with two varying microstructures, bimodal and acicular respectively. The two different initial microstructures were treated thermally by aging at 515 °C, 545 °C, and 575 °C at different times from 1 min to 576 h to induce a precipitation process. Ultrasonic measurements of shear and longitudinal wave velocities, scanning electron microscopy (SEM) image processing and micro-hardness were performed, establishing a direct correlation with the measurements of the ultrasonic velocity and the elastic properties developed during the thermal treatment of the artificial aging. The results of the ultrasonic velocity show a very clear trend as the aging time progresses, which is affected by precipitation of Ti3Al particles inside the α phase. In this way, we can know, in a fast and efficient way, the elastic properties developed during the heat treatment of aging at long times, since the presence of these precipitates hardens the material microstructure affecting the final mechanical properties.

Processing of in situ Al3Ti/Al composites by advanced high shear technology: influence of mixing speed

High shear technology (HST) is an advanced melt stirring technology with the intensive shear effect and allows the production of particle-reinforced Al composites (PAMCs) with a homogeneous particle distribution. In the fabrication process, applying an appropriate mixing strategy to obtain the excellent microstructure and properties is crucial. In this work, Al3Ti/Al composites with different Al3Ti volume fractions were fabricated in situ by high shear technology at various mixing speeds. The effect of mixing speed on the microstructure and mechanical properties was investigated. The results show that the reaction rate and Al3Ti particle size increase with the increase of mixing speed. An intermediate mixing speed is appropriate for preparing the Al3Ti/Al composite with a homogeneous distribution of reinforcing particles and low porosity. A lower mixing speed leads to severe particle agglomerations, which deteriorates the ductility of Al3Ti/Al composites. A higher mixing speed results in high porosity within castings resulting from severe air entrainment, which significantly reduces mechanical properties. Young’s modulus improves with increasing the stiff Al3Ti particle content and matches well with the predicted results as well. Tensile and compression strength and hardness are enhanced due to generating the uniform distribution of reinforcing particles and the matrix grain refinement.

Production and properties of functionally graded hybrid composites containing Al3Ti and TiB2

AbstractThis study examined the production and properties of functionally graded hybrid composites containing titanium di-boride (TiB2) and titanium tri-aluminate (Al3Ti) particles. The composites were produced by the centrifugal solid particle method at 850 °C. A detailed study of the microstructures, hardness and abrasive wear behavior of the hybrid composites was carried out. The results showed that the produced composites had three different regions along the centrifugal force direction. It was found that there were Al3Ti particles in the outer region, TiB2 particles in the middle region and neither Al3Ti nor TiB2 particles in the inner region of the functionally graded composites. It was determined that the abrasive wear properties of the composites were improved by 5 times with about 33 wt.% Al3Ti and by 3 times with about 7 wt.% TiB2 in comparison to the pure aluminum matrix.

Novel intermetallic-reinforced near-α Ti alloys manufactured by spark plasma sintering

Near-α Ti alloys are ideal candidates for high-temperature aerospace, automotive and nautical propulsion systems due to their high strength, low density and good corrosion resistance. However, the maximum service temperature of the well-known near-α alloy Ti6242S is limited to about 540 °C. By adding, for example, intermetallic γ-TiAl based alloy particles to Ti6242S powder a significant increase in yield strength up to 650 °C can be achieved by means of spark plasma sintering, along with sufficient room temperature ductility. In this study, investigations on the underlying strengthening mechanisms were carried out. For this purpose, mechanical tests and detailed microstructural characterization were performed.Spark plasma sintering at 1150 °C of powder blends with 10 m.% spherical γ-TiAl based powder (<20 μm) leads to a homogeneous dissolution of the TiAl particles in the matrix material and a refinement of the lamellar microstructure. Due to the formation of ordered intermetallic α2-Ti3Al precipitates, which are completely stable up to 670 °C in the newly evolved Ti-8.3Al-1.8Sn-3.7Zr-2.0Mo-0.9Nb-0.08Si alloy (m.%), the creep resistance at 600 °C has been increased significantly. In the B containing variant, it was found that finely distributed titanium borides TiB formed in the Ti6242 matrix and led to an even more pronounced refinement of the microstructure. For B additions of 1 m.%, however, the creep resistance at 600 °C is reduced compared to the other alloys, but the strength is increased up to 500 °C.

Tailoring microstructure and its effect on wear behavior of an Al–7Si alloy reinforced with in situ formed Al3Ti particulates

The microstructure and wear behavior of an Al–7Si alloy reinforced with in situ Al3Ti particulates were studied. The effects of Sr modification and heat treatment were also investigated. Sr and Al3Ti particulates had clear effects on modifying the morphology of eutectic Si and the microstructure of the Al–Si alloy, playing a key role in improving the hardness and wear properties of the Al3Ti/Al–7Si–Sr composite. T6 heat treatment was performed to spheroidized coarse eutectic Si, reducing stress concentration and further improving the hardness and wear properties of the composites. Among them, the Al3Ti/Al–7Si–Sr composite displayed the highest hardness and the lowest friction coefficient in both as-cast and T6 heat treated states attributed to the combined effects of Sr modification and Al3Ti reinforcement.

Evolution and micromechanical properties of interface structures in TiNbf/TiAl composites prepared by powder metallurgy

TiNbf/TiAl composite has enormous potential to serve on advanced aerospace equipment, but brittle reaction products limit the further improvement of overall toughness; meanwhile, the types and contents of interface reaction products remain controversial. This study is to clarify the evolution process of interface reaction structure in TiNbf/TiAl composite and explain it from the perspective of thermodynamics. This study discovered that brittle interface can transform into a relatively ductile interface containing two kinds of α2/γ lamella colonies above the transition temperature of 1200 °C. The relative sizes of γ and α2 lamella thickness varied in two different lamellar colonies. Above 1200 °C, recrystallization process at the boundary of original TiAl particles was completed and all defects were eliminated completely either. Gibbs free energy (ΔG) of every phase (γ, α2, β and other generated intermetallics) calculated based on element distribution model is consistent with the experiment results well. Micromechanical properties tested by nanoindentation suggest that the interface in the form of lamella colonies had relieved variation amplitudes of reduced modulus Er and hardness H across the interface region which may show beneficial influences on improving toughness of TiNbf/TiAl composite.

Formation kinetics and phase stability of in-situ Al3Ti particles in aluminium casting alloys with varying Si content

The intermetallic phase Al3Ti is a promising candidate to increase the stiffness of aluminium casting alloys due to its high Young’s modulus. The phase is formed by the in-situ reaction between solid titanium particles and the liquid aluminium melt. High-shear mixing technology is used to peel off the reaction layer on the surface of the Ti particles and distribute the Al3Ti particles homogeneously in the melt. This work investigates the influence of the Si content of three different aluminium casting alloys on the in-situ reaction. Additionally, the influence of the initial titanium powder particle size and the process temperature on the formation kinetics are investigated.

Microstructure and mechanical behavior of Al–TiAl3 composites containing high content uniform dispersion of TiAl3 particles

The microstructure, mechanical behavior and deformation mechanisms of Al–TiAl3 composites containing a wide range of volume fraction of TiAl3 (Vp: 24.6–89.0%) with uniform distribution were investigated. Microhardness and strength of the composites increase with increasing Vp of TiAl3 particles, reaching ~11.0 times and ~8.0 times those of the matrix respectively. While the strength of the composites can be correlated well to the comprehensive contributions of various strengthening mechanisms of the matrix for low Vp, that for high Vp was found to fit to direct contributions from both the matrix and particle following the law of mixture. Besides the deformation of the matrix, evident plastic deformation of TiAl3 particles by dislocation activities as well as twinning was observed in the composites upon loading at room temperature. Two mechanisms for crack initiation inside the TiAl3 particle were identified, namely by intersection of twins and by interaction between dislocations and twins. Microcracks tend to propagate along the twin boundaries in TiAl3 particles and were found to be suspended at the particle/matrix interface. The unique deformation behavior of TiAl3 particles in the composites can be attributed to the uniform distribution of TiAl3 particles that ensures a continuous network of surrounding matrix even at very high Vp.