TiAl Phase Research Articles

INFLUENCE OF GEOMETRICAL DESIGN ON FRICTION-WELDED AA6061/Ti6Al4V JOINTS FOR WING SPARS OF AIRCRAFT STRUCTURES

In aerospace industry, there is a need for aluminum/titanium joints in wing spars of aircraft structures. This research explores the feasibility of joining Ti6Al4V to AA6061 by means of friction welding. Influence of geometrical design on the microstructure and impact strength of dissimilar AA6061/Ti6Al4V joints is investigated. Investigation by scanning electron microscopy reveals deformation of the grains at titanium side along the direction of stress, therefore leading to the formation of TMT (thermo-mechanically treated) zone. The intermetallic compound at the joint interface is attributed to the presence of brittle TiAl and Ti3Al phases. Rotational speed has a significant influence on the impact strength. The impact energy at the interface was found to be 10.2[Formula: see text]J when the speed of rotation was set as 1000[Formula: see text]rpm. Geometry featuring “spearhead with blunt end” is found to give good joint strength with minimum material loss. Fractography studies reveal the presence of few dimples in the welded zone and brittle mode of fracture.

Effect of Al–5Ti–1B grain refiner on microstructure and properties of arc-additive-manufactured Al–Mg alloy

In this study, a strip-shaped Al–5Ti–1B grain refiner was employed to produce Al–Mg alloy using cold metal transfer arc additive manufacturing. The microstructure and mechanical properties of the straight-wall samples (SWSs) were analyzed. The results indicated that the Al3Ti phase occurred in SWS with Al–5Ti–1B, and acted as heterogeneous nucleation sites during solidification. Formation of Al3Ti particles led to the transformation of the columnar grains between the layers into equiaxed grains and refined the grains at the center of the layers. Furthermore, the Al3Ti particles increased the fraction of low-angle grain boundaries by 8.2%. In addition, the anisotropy in mechanical properties (i.e. tensile strength and elongation) was reduced significantly. Also, the low hardness zone between the layers was eliminated. Thereby, improving the mechanical properties of the additive-manufactured Al–Mg alloy samples.

Analysis of dissolved titanium concentration and phase transformation in molten Al[sbnd]Ti alloy using laser-induced breakdown spectroscopy

We report Ti concentration measurements in dilute AlTi alloys, acquired from direct analysis of the molten metal by laser-induced breakdown spectroscopy (LIBS). The LIBS analysis showed approximately constant Ti concentrations at melt temperatures above the liquidus, while at lower temperatures the measured concentration followed the L/(L + Al3Ti) liquidus of the phase diagram, confirming that the LIBS measurement accurately detects the dissolved Ti concentration in the melt. The LIBS measurements furthermore demonstrated that the Al3Ti phase forms or dissolves within minutes when the melt temperature is decreased or increased, respectively. For the first time, the liquidus line at low Ti concentrations in the AlTi phase diagram has thus been mapped using LIBS analysis instead of the more conventional but time-consuming thermal analysis methods. We conclude that LIBS analysis of molten metal offers a unique opportunity to monitor accurately the chemical composition of the liquid phase and reveal the formation of solid precipitates in real time.

The preferential formation of Ni2Al3, Fe2Al5, and Ti2Al5 phases in aluminide systems

The preferential formation of phases in Ni–Al, Fe–Al, and Ti–Al systems was observed at the interface of solid-solid and solid-liquid phases. It was found that phases already formed at temperatures lower than the melting point of aluminum. The Ni2Al3, Fe2Al5 and Ti2Al5 phases formed preferentially in the Ni–Al, Fe–Al and Ti–Al systems, respectively. The favored formation was not associated with thermodynamic assumptions, but was caused by crystal structures of arisen phases. The mentioned phases could form due to the two reasons, (i) similarities of their lattice parameters to lattice parameters of the individual elements (Ni, Fe, Ti, or Al) and (ii) the total volume of its lattice. The lattice volumes of Ni2Al3, Fe2Al5, and Ti2Al5 phases are always smaller than that of NiAl3, FeAl3, and TiAl3 phases. The last listed phases are ordinarily accepted by other authors as the phases, which form preferentially based on thermodynamic data only. This work disproves such claims and shows the reason for preferential phases' formation.

Microstructure and Phase Evolution Characteristics of the In Situ Synthesis of TiC-Reinforced AZ91D Magnesium Matrix Composites.

TiC-reinforced AZ91D magnesium alloy composites were synthesized through the in situ reaction between an AZ91D melt and Ti-C-Al preforms. The microstructural evolution characteristics and phase transformation were investigated at different melt reaction temperatures (1013, 1033, and 1053 K), with the aim of understanding the in situ formation mechanism of TiC particles from thermodynamic and kinetic perspectives. The results showed that the temperature played a critical role in determining the formation and morphology of TiC. Initially, only the Al3Ti phase was formed through the reaction between Ti and Al when the temperature was 1013 K. With the increase in the melt temperature, the A13Ti’s thermodynamic stability decreased, and dissolution and precipitation reactions occurred at higher temperatures (1033 and 1053 K, respectively), contributing to the formation of TiC particles. The formation of the TiC phase was attributed to two factors: Firstly, A13Ti as an intermediate product reacted with carbon and formed TiC with increasing temperature. Secondly, the in situ TiC reaction was promoted due to the increased reaction-driving force provided by the increasing temperature.

Insights into Poisoning Mechanism of Zr by First Principle Calculation on Adhesion Work and Adsorption Energy between TiB2, Al3Ti, and Al3Zr

Al-Ti-B intermediate alloys are widely used as grain refiners in aluminum alloys owing to the presence of Al3Ti and TiB2 phases. However, the existence of Zr in aluminum alloy melts often results in coarse grain size, leading to Al-Ti-B failure called Zr poisoning. There are three kinds of poisoning mechanisms related to TiB2, Al3Ti, and a combination of TiB2 and Al3Ti for Zr. First, Zr forms ZrB2 or Ti2Zr with TiB2 in Al-Ti-B to reduce the nucleation ability. Second, Zr existing in the aluminum melt with a high melting point Al3Zr then attracts Ti to reduce the dispersion of Ti as a growth inhibitor. Third, Zr reacts with Al3Ti on TiB2 surface to form Al3Zr, thereby increasing the degree of mismatch with Al and diminishing the refiner’s ability as a nucleation substrate. To gain a better understanding of the mechanism of Zr poisoning, the first principle was used in this study to calculate the adhesion works (ZrB2//Al3Ti), (Ti2Zr//Al3Ti), (Al3Zr//Al3Ti), (Al3Ti//Al), (TiB2//Al3Zr), and (Al3Zr//Al), as well as the surface energy of Al3Zr and adsorption energies of Al to Al3Ti or Al3Zr. The results demonstrated that Zr poisoning originated from the second guess. Zr element exiting in aluminum melt led to the formation of an Al3Zr (001) surface. The interfacial adhesion work of Al3Zr (001)//Al3Ti (001) was not weaker than that of TiB2//Al3Ti. As a result, Al3Zr first combined with Al3Ti to significantly decline the adsorption of Al3Ti (001) on Al, losing its role as a nucleating agent and grain coarsening. Overall, to prevent failure of the grain refiner in Zr containing aluminum melt, the adhesion work interface between the generated phase of the grain refiner and Al3Zr must remain lower to avoid the combination of the generated phase of grain refiner with Al3Zr. In sum, these findings look promising for evaluating future effects of grain refinement in Zr containing aluminum melt.

Microstructure and wear behavior of AlCrTiNbMo high-entropy alloy coating prepared by electron beam cladding on Ti600 substrate

High-entropy alloys have been widely studied as a new and excellent material in the field of surface protection. To improve the low surface hardness and wear resistance of Ti600 alloy, AlCrTiNbMo high-entropy alloy (HEA) coating was prepared by electron beam cladding. The phase structure and microstructure showed the presence of two BCC solid solution phases A2 and B2 within HEA coating. Laves phase Ti3Al and intermetallic compound Mo3Al8 were also present in the coating. The results of hardness and wear resistance tests showed that the microhardness of coating is 813.5 HV0.2，while substrate is 370.7 HV0.2. The mass loss of coating is only 1.02 mg after wear test, while the mass loss of Ti600 is 38.81 mg. There are cracks and delaminations on the worn surface of Ti600, and wear mechanism is a mixture of micro-ploughing and micro-cutting. The worn surface of HEA coating contains only shear surface traces, and the wear mechanism is micro-cutting. The width and depth of grooves on the worn surface of HEA coating are nearly 10 times that of Ti600 substrate. AlCrTiNbMo HEA coating can be used as an excellent wear-resistant coating with wide application prospect.

Formation mechanism and growth kinetics of TiAl3 phase in cold-rolled Ti/Al laminated composites during annealing

Cold-rolled Ti/Al laminated composites were annealed at 525–625 °C for 0–128 h, and the interfacial microstructure evolution was investigated. The results indicate that only the TiAl3 phase was formed at the Ti/Al interface; most of TiAl3 grains were fine equiaxed with average sizes ranging from hundreds of nanometers to several microns and the TiAl3 grain size increased with increasing annealing time and/or temperature, but the effect of annealing temperature on the TiAl3 grain size was far greater than that of annealing time. The growth of the TiAl3 phase consisted of two stages. The initial stage was governed by chemical reaction with a reaction activation energy of 195.75 kJ/mol, and the reaction rate constant of the TiAl3 phase was larger as the Ti/Al interface was bonded with fresh surfaces. At the second stage, the growth was governed by diffusion, the diffusion activation energy was 33.69 kJ/mol, and the diffusion growth rate constant of the TiAl3 phase was mainly determined by the grain boundary diffusion owing to the smaller TiAl3 grain size.

Effect of Solution Treatment and Aging Temperature on α′ and Ti3Al(α2) Phase Formation and Mechanical Properties of Water-Quenched Ti–6Al–4V

Effect of Solution Treatment and Aging Temperature on α′ and Ti3Al(α2) Phase Formation and Mechanical Properties of Water-Quenched Ti–6Al–4V

Tensile property and microstructure assessment of hydrogen treated Ti-6Al-4V alloy

Temporary hydrogen alloying (THA) treatment was used to refine the coarse-grained microstructure of a Ti-6Al-4V alloy with the intention of modifying tensile strength and ductility. Microstructure evolution was characterised using X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results indicate that THA treatment does not refine the coarse network of prior beta grains, but it alters the coarse Widmanstätten microstructure by nucleating submicron beta grains within the individual lamellae. The modified microstructure increases ultimate tensile strength (UTS) in the order of 100 MPa. The dehydrogenation temperature affected tensile ductility. The lowest dehydrogenation temperature (675 °C) had the highest ductility loss, and increasing the dehydrogenation temperature recovered ductility until full ductility was recovered at 750 °C. The ductility loss was attributed to the embrittling effect of the hydrogen induced phase Ti3Al which remains in the microstructure even after hydrogen removal and only completely dissolves at 750 °C. The results demonstrate that THA treatment significantly alters the initial coarse-grained microstructure with concomitant improvement in strength, but that the promotion of Ti3Al precipitation can cause embrittlement unless the dehydrogenation treatment is controlled to optimise Ti3Al dissolution.

In-situ Al3Ti particle reinforcement for stiff aluminum die castings

The intermetallic phase Al3Ti is a promising candidate to increase the stiffness of aluminum casting alloys due to its high Young’s modulus. Reinforcement particles are formed by the in-situ reaction between solid titanium particles and the liquid aluminum melt. A high-shear mixer 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 dissolution velocity of different size fractions of Ti powder in three different aluminum casting alloys. The results were used to fabricate specimens with different volume fractions of Al3Ti particles by high pressure die casting. Microstructure characterization was performed to investigate the distribution of the Al3Ti particles within the castings. The mechanical properties were determined by tensile tests and resonant frequency analysis.

Temperature dependent anisotropic mechanical behavior of TiAl based alloys

γ-based titanium aluminides exhibit remarkable mechanical properties at high temperatures and are deployed in jet engines. The microstructure of these alloys, consisting of alternating plates of the γ (TiAl) and α2 (Ti3Al) phases, exhibits highly anisotropic mechanical behavior. However, deep understanding of the associated micromechanics is lacking. The effect of differential strength of the slip/twin systems, structural length scales and temperature in determining the homogeneity of deformation at the intercolony and intracolony level has not been well understood. Hence, we establish structure–property relationships, under uniaxial compression and uniaxial tension, by crystal plasticity finite element techniques. The deviation from Hall–Petch behavior and the temperature-dependent yield stress anomaly are rationalized and included in the model. Our results reveal a complex interplay between lamellar orientation, structural length scale, temperature, and stress state. Key findings include: (1) Basal slip in the α2 phase can be activated by differential strengthening of slip systems at lamellar interfaces. Basal slip increases the propensity for crack nucleation due to coarse slip bands. (2) There is preferential activation of twinning in the γ phase under tension. These twins can improve ductility by increasing strain hardening. However, they can also promote crack nucleation. (3) Smaller lamellar widths at higher temperatures can improve strain homogeneity between the γ and α2 phases. (4) Yield stress anisotropy exhibited a non-monotonic variation with lamellar size and temperature. (5) Increasing the strength of slip/twin systems through solid solution or precipitation strengthening can improve intracolony deformation homogeneity, reducing crack nucleation. We suggest strategies for alloy and microstructure design to improve damage tolerance in these alloys.

The electrochemical corrosion behaviour of Ti-48Al-2Nb-0.7Cr-0.3Si alloy in 3.5%NaCl

Titanium aluminides (TiAl) have attracted industrial interest, particularly for high temperature applications owing to their promising mechanical properties. Due to the application of these materials to the marine environment it is therefore important to understand their performance under such conditions. In this study, the corrosion behaviour of Ti-48Al-2Nb-0.7Cr-0.3Si alloy produced by vacuum arc melting was investigated using the potentiodynamic polarization method. The corroded surface and Ti-Al phases were investigated by scanning electron microscopy (SEM), optical microscopy, and X-ray diffraction (XRD). Hardness was examined by a Vickers micro hardness tester with a diamond indenter. Pitting was observed to occur within the surface defects and caused severe corrosion.

Laser micro in situ alloying of γ-Ti46.8Al1Cr0.2Si with Manganese

Titanium alloys have two primary phases (α + β) that are attributed to the α-stabiliser (aluminium) and β-stabiliser (niobium). The latter stabilisers shift α-phase to higher temperature while the former stabilisers shift the β-phase to lower temperatures. To extend their scope of application, (α + β)-phase titanium alloys can be micro-alloyed with β-eutetic elements (Mn, Cr, Si, Co etc) to form intermetallic compounds which are typically referred to as titanium aluminides (Ti-Al). Several intermetallic alloys can be formed in the Ti-Al phase diagram but only (α2)-Ti3Al and (γ)-TiAl are stable and of relevance to structural engineering since they can be used in industries spanning across energy, aerospace and tissue-engineering. In this study, a castable γ-Ti46.8Al1Cr0.2Si pre-alloyed powder, was micro-alloyed with Mn in order to examine if it can improve its tensile properties. When 1–2 at. % Mn is added to Ti-Al alloys, it is able to increase ductility, reduce oxidation resistance and shift the (α2 + γ)/ γ to the titanium side and decrease the Al content in the γ-phase. To effectively ascertain these effects Mn feed rates were varied from 0.2 to 1.0 rpm during the micro-alloying of γ-Ti46.8Al1Cr0.2Si through in-situ laser deposition to form γ-Ti46.8Al1Cr0.2Si-(xMn). The produced clads were characterised for chemistry and microstructure using scanning electron microscope. Results concluded that Al content decrease with an increase in Mn from 56 at. % to 49 at. %. Mn of 10.16 g/min had similar properties to the non-Mn alloyed sample. Moreover, it was shown in this work that laser processing decreased the tensile and yield strength of the alloy when compared to the as-cast in previous studies, and that 2.69 g/min and 10.16 g/min are lower and upper Mn values when ductility of the master alloy is to be improved.

Formation mechanism of Ti3AlC2 in TiO2–Al–C/TiC systems at high temperatures

Ti 3 AlC 2 /Al 2 O 3 composites were synthesized by aluminothermic reduction of TiO 2 /Al/C and TiO 2 /Al/TiC. The effects of carbon sources (carbon black and TiC), steps heating-up profile, and Al-excess of raw materials composition on the Ti 3 AlC 2 content in final products were investigated. The results showed that in contrast with carbon black, TiC used as a carbon source is beneficial to the formation of Ti 3 AlC 2 at lower temperatures. However, Ti 3 AlC 2 content in the product with carbon black was improved by the steps heating-up profile and Al-excess, promoting intermediate phases TiAl 3 and TiC. Furthermore, the formation mechanisms of Ti 3 AlC 2 with different carbon sources in aluminothermic reaction systems were also elucidated. For the TiO 2 /Al/C system, Ti 3 AlC 2 is precipitated from the Ti–Al melt at high temperatures via the dissolution-precipitation mechanism, which has slower nucleation but faster growth. In contrast, in the TiO 2 /Al/TiC system, Ti 3 AlC 2 is mainly growing from the intact TiC grains through the epitaxial nucleation mechanism, which has faster nucleation but lower growth.

Effect of micron-Ti particles on microstructure and mechanical properties of Mg–3Al–1Zn based composites

In the field of metal matrix composites, it is a great challenge to simultaneously improve the strength, ductility and elastic modulus of magnesium matrix composites (MMCs). In this work, Mg–3Al–1Zn composites reinforced with micron-Ti particles were prepared by powder metallurgy. The results show that the yield strength, elongation and elastic modulus simultaneously were increased with increasing content of Ti particles. Through diffusion, Ti and Al formed TiAl phase at the edge of Ti particle. A nanoscale layer of MgO formed between TiAl and magnesium (Mg) matrix. The 9Ti/Mg–3Al–1Zn composite obtained the best comprehensive mechanical properties with yield strength, ultimate tensile strength and elongation of 264 MPa, 294 MPa and 8%, respectively. The increased strength is mainly due to the grain refinement and strong interfacial bonding between Ti particles and Mg matrix. The improved ductility is the result of refined grains, weakened texture and collaborative deformation of Ti particles.

Исследование режимов изнашивания композиционного материала на основе антифрикционного сплава АОМ20-1 упрочненного частицами Ti

Сomposite material samples were obtained by the method of reaction casting by mixing titanium particles to obtain intermetallic phases Al3Ti. Dry sliding wear tests were carried out using a fixed sleeve (steel 45) against a rotating disk (sample) at sliding speeds from 0.25 to 0.75 m/s and loads from 0.5 to 3.5 MPa.There were constructed maps of wear rate, which determine the friction modes during testing. There were shown boundaries and conditions of changing wear modes.

Effect of spark plasma sintering and reinforcements on the formation of ultra-fine and nanograins in AA2024-TiB2-Y hybrid composites

This study reports the influence of sintering mechanism and reinforcement materials on the formation of ultra-fine and nanograins in Al-TiB2-Y nanohybrid composites. The mechanical properties of the composites and their corresponding micro and nanostructures are correlated. The experimental and characterization results revealed that despite the addition of TiB2, the hard and brittle Al3Ti phase formation in the composites was suppressed and hence, their ductility was retained. It was found that yttrium content of 0.3 ​wt% was the optimum amount which created advantageous spark plasma sintering conditions, and the addition of 0.3 ​wt% promoted the formation of bi-modal size grains (ultra-fine and nano) along with micro grains, Ω and other nano precipitates, resulting in a significant enhancement in the composite properties. The formation of ultra-fine and nanograins may be attributed to the combined effect of melting and rapid solidification at necking zones due to Joule's heating and thermo-mechanical fatigue. Among all the sintered composites, the highest hardness (137 HV), ultimate tensile strength (UTS) (496 ​MPa), yield strength (YS) (438 ​MPa) with 15.7% elongation were obtained in the sintered sample reinforced with 1.0 ​wt% TiB2 and 0.3 ​wt% yttrium.

Влияние Nb, Zr и Zr+Hf на параметры решеток интерметаллидных фаз и сопротивление ползучести γ-TiAl сплавов на основе Ti-44Al-0.2B

X-Ray diffraction (XRD) analysis was used to study the influence of alloying with 5 at.% Nb, 5 at.% Zr and 5 at.% (Zr+Hf) on the lattice parameters of the γ(TiAl) and α2(Ti3Al) phase in the intermetallic alloys based on Ti-44Al-0.2B (at.%). Before XRD analysis duplex structures with near the same microstructural parameters were obtained in samples of the alloys. The XRD data were used to calculate the tetragonal distortion (cγ / aγ ratio) of the γ phase, the cα2 / aα2 ratio of the α2 phase and the γ / α2 lattice misfits of the alloys. The highest tetragonal distortion (cγ / aγ) of the γ unit cell (cγ / aγ =1.0124) is observed for the base Ti-44Al-0.2B alloy, followed by the Nb-, (Zr+Hf)- and Zr-containing alloy (cγ / aγ =1.0116, 1.0075 and 1.0069, respectively). The cα2 / γα2 ratio is insignificantly changed depending on alloying. Doping with Zr and Zr+Hf leads to a noticeable decrease in the γ / α2 lattice misfits as compared with the alloy doped with Nb and the base alloy. For instance the γ / α2 lattice misfits determined in both crystallographic directions of the γ phase in the Ti-44Al-5Zr-0.2B and Ti-44Al-5Nb-0.2B alloys were found to be ε110 / ε101= 0.93 / 0.59 and ε110 / ε101=1.38 / 0.79, respectively. It has been recently revealed that γ-TiAl alloys with near the same duplex structures based on Ti-44Al-0.2B and doped with Zr and Zr+Hf demonstrated appreciably higher creep resistance than the alloy doped with Nb and the base alloy. It is assumed that the lower cγ / aγ ratios obtained for the Zr- and (Zr+Hf)-containing alloys contribute to the reduction of creep resistance. The fact that the Zr- and (Zr+Hf)-containing alloys showed higher creep resistance than the Nb-containing alloy should be mostly attributed to the lower γ / α2 lattice misfits in the Zr- and (Zr+Hf)-containing alloys and the higher solution hardening caused by doping with Zr and Hf. Therefore, the impact of alloying on the creep and heat resistance in β-solidifying γ-TiAl alloys should be considered taking into account the changes of the lattice parameters of the γ(TiAl) and α2(Ti3Al) phase, which influence the physical processes determining the creep behavior.

Laser-induced dynamic wetting behavior and interfacial evolution of AlSi5 alloy on Ti6Al4V alloy

Compared with isothermal wetting, laser-induced wetting behavior exhibited a significant contrast within the spreading mechanism owing to the short thermal cycle and migration driven by the thermal gradient. In this study, laser-induced wetting behavior of AlSi5 alloy on Ti6Al4V substrate was investigated. The process was captured by a self-built dynamic data acquisition device and interfacial microstructure evolution was explored. The mechanism for spreading was evaluated by finite element simulation, spreading dynamic and thermodynamic analysis. The wetting process was controlled by reaction product at the early stage and dominated by adsorption of elements at a later stage. The wettability was promoted with increasing irradiation time until 1.4 s. After prolonged irradiation, IMC composed of TiAl3 phase evolved from granular to rod-shape. Continue to irradiate, multiple Ti-Al phases and Ti5Si3 precipitates were produced. At central zone, Al atoms were more likely adsorbed onto Ti substrate, which facilitated the growth of Ti-Al phases. At front zone, the adsorption rate of Si atoms onto Ti substrates was accelerated and the decomposition of Si-rich phase further promoted the spreading. The elucidated relationship between wetting and microstructure could provide a reliable guide for obtaining relatively good wetting without generating over-thick compounds.