TiAl Phase Research Articles

Mechanical and Corrosion Properties of VT6 Titanium Alloy after Irradiation with Helium and Aluminum Lons

The effect of high-dose aluminum implantation on the structural-phase state of the surface layer of titanium alloy VT6 with a fine structure (average grain size 2.3 μm) on the mechanical and corrosion properties has been investigated. It is shown that, as a result of ion irradiation, polyphase implanted layers based on α-titanium grains are formed, containing an intermetallic Ti3Al phase along the grain boundaries of α-titanium. The modified surface layers are characterized by improved mechanical properties and corrosion resistance. The noted effect is enhanced by the use of preliminary helium implantation with a dose of 1.3 × 1017ion / cm2.

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.

Fabrication, Microstructure, and Microhardness at High Temperature of In Situ Synthesized Ti3Al/Al2O3 Composites

In this study, in situ Al2O3-reinforced Ti3Al composite was fabricated after 8 h of milling and sintering at 850 °C. A mixture of TiO2 and Al powders were mechanically milled in a planetary mill, cold-compacted and sintered under a protected argon atmosphere. The microstructure and microhardness of the Al2O3 embedded in Ti3Al matrix at both room and elevated temperature has been reported. The obtained results showed that the Ti3Al/Al2O3 composite was successfully synthesized via the powder metallurgy method. Ti3Al phase and Al2O3 particles were formed after 8 h of milling and sintering at 850 °C. The microstructure formation of round and uniformly distributed Al2O3 particles in the Ti3Al matrix improved the microhardness of the composite. At normal temperature, the microhardness of the material measured about 11.5 GPa. Meanwhile, at elevated temperatures, from 600 to 800 °C, it decreased from 4.18 GPa to 3.15 GPa.

Preparation of in-situ TiB2 reinforced aluminum matrix composites assisted by two steps of ultrasonic vibration

The TiB2/Al particle reinforced composites were prepared successfully through metal-salt reaction with different process conditions (mechanical stirring, one-stage and two-stages of ultrasonic vibration). It was usually taken more than 60 min to complete metal-salt reaction under mechanical stirring condition, lots of reinforcement agglomerations and residual intermediate such as Al3Ti was in the matrix. The reaction time was greatly shortened from 60 min to 5 min and particle agglomerations were eliminated successfully by the introduction of ultrasonic vibration at 850 °C. Through the introduction of ultrasonic vibration at 730 °C, not only most of the residual Al3Ti phase was broken or dissolved, but also the size of TiB2 was refined. The composite prepared by two-stage ultrasonic vibration has the optimal improvements of yield strength and ultimate tensile strength, which increased by are 108% and 98% respectively, hardness increased 61.5%. When only introducing the first stage of UVT, the elongation decreased from 34% to 20% owning to lots of rod-like Al3Ti in the matrix, after the second stage of UVT, the elongation restored to 33%. The effects of ultrasonic vibration on phase transformation, microstructure, and mechanical properties were studied by x-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM) and Electron Backscattered Diffraction (EBSD). Moreover, the effects of Orowan strengthening, thermal expansion mismatch strengthening, and grain refinement strengthening on mechanical properties were also discussed.

Increasing the oxidation resistance of γ-TiAl by applying a magnetron sputtered aluminum and silicon based coating

In this study, the suitability of a magnetron sputtered Al–18Si (at.%) coating as oxidation protection for a γ-TiAl based TNB-V2 alloy was investigated. The coating microstructure and its changes as well as the evolution of the different phases during the different steps, deposition process, post heat treatment and isothermal oxidation test, was studied using x-ray diffraction as well as scanning and transmission electron microscopy.The well adherent coating provides a homogenous, dense and crack free crystalline microstructure of Si grains in an Al matrix. The phase evolution analysis during a 20 h post-heat treatment at 550 °C with in situ x-ray diffraction reveals the complete formation of the TiAl3 phase due to the reaction of Ti from the TNB-V2 substrate and Al from the coating. During oxidation at 850 °C for 300 h, a thermally grown α-Al2O3 layer was formed providing excellent oxidation resistance. The formation of α-Al2O3 relies on the presence of TiAl3 whereas the silicon acted as a getter for Ti and thus could prevent the formation of TiO2. Furthermore, the finally formed Ti5Si3 phase reduces the inwards diffusion of Al into the substrate and prevents fast Al depletion in the coating. Moreover, the hierarchical coating microstructure, consisting of a TiAl3 matrix with a network-like structure of the Ti5Si3 phase, could be beneficial in terms of mechanical properties.

Microstructure Evolution and Mechanical Performances of SiCf Reinforced (Al3Ti + Al3Ni)-Based Metallic–Intermetallic Laminate Composite

In present work, a novel SiCf reinforced (Al3Ti + Al3Ni)-based metallic–intermetallic laminate (Ti–(Al3Ti + Al3Ni)/SiCf-MIL) composite without centerline defect was prepared using Ti, Al foils, NiTi wires and SiC fibers by vacuum hot pressing sintering method. Electron backscatter diffraction was employed to characterize the microstructure and phase constituents of Ti–(Al3Ti + Al3Ni)/SiCf-MIL composite during various stages of preparation process. The elimination mechanism of intermetallic centerline was discussed. Besides, quasi-static compressive performance and fracture toughness of the synthesized composite were investigated. The experimental results indicated that as reaction time increasing, the NiTi/Al interfacial reaction occurred prior to the Ti/Al interfacial reaction to form an Al3Ti/Al3Ni zone. Then, the oxides gathered at the front of Ti/Al interfacial reaction layer were dispersed in the intermetallic layer rather than being pushed together to generate the centerline due to the Al3Ti/Al3Ni zone. After reaction, there were no residual NiTi phases and intermetallic layers mainly consisting of Al3Ti and Al3Ni phases were obtained in this composite. In addition, high angle grain boundaries in Al3Ti grains occupied a large proportion, conversely, low angle grain boundaries dominated in Al3Ni grains. Furthermore, stress concentration appears at the interface between layers instead of along the middle plane of intermetallic layer. Moreover, both compressive strength and fracture toughness of the composite are superior in comparison with SiCf reinforced Ti–Al3Ti metallic–intermetallic laminate composite (Ti–Al3Ti/SiCf-MIL) ascribed to the elimination of centerline.

Characterization based analysis on TiAl3 intermetallic phase layer growth phenomenon and kinetics in diffusion bonded Ti/TiAl3/Al laminates

In this article, new insights towards the layer growth phenomenon of TiAl3 phase in alternative Ti/Al based multilayer metal intermetallic laminate is discussed. Ti/Al multilayered metal intermetallic laminates were prepared at two different temperatures of 550 and 575 °C using solid-state diffusion bonding technique. TiAl3 was the only intermetallic layer formed along the Ti/Al metallic layer interfaces at the processed temperatures. The TiAl3 intermetallic layer grows (thickens) in two stages with respect to diffusion duration with each stage controlled by different growth phenomena viz. chemical reaction-controlled and diffusion-controlled growth respectively. The initial nucleation of TiAl3 grains takes place by chemical reaction between Ti and Al atoms without any specific nucleation sites in the intermix zone. Whereas, the triple junctions of the initially nucleated TiAl3 grains acts as a preferred TiAl3 nucleation site for further layer growth during reaction-controlled growth stage. During diffusion-controlled growth, the preferred nucleation site shifts to Ti/TiAl3 and Al/TiAl3 interfaces which makes the TiAl3 layer growth to be predominantly controlled by the diffusivities of Ti and Al atoms. The growth kinetics study exhibits higher layer growth rate during diffusion-controlled growth stage which is mainly due to faster Al diffusion and higher TiAl3 nucleation rate at Ti/TiAl3 interface.

Creep behaviour of two-phase lamellar TiAl: Crystal plasticity modelling and analysis

Two-phase (α2Ti3Al+γTiAl) fully lamellar TiAl alloys show highly anisotropic creep behaviour. Depending on lamellar orientations, locally in the TiAl phases hard and easy deformation modes are active, which significantly influence the creep behaviour at a global scale. To obtain comprehensive understanding how the locally activated crystallographic deformation modes influence the macroscopic creep behaviour, a crystal plasticity (CP) model with modified hardening behaviour is proposed in this work. For this purpose, a softening parameter is introduced in the model that phenomenologically describes the threshold stresses for material softening depending on pile-up dislocation lengths during creep deformation. The model allows us to interpret the cause of creep anisotropy at macro-scale deformation based on the orientation dependent activation and interactions of slip systems at the TiAl phases. Comprehensive study was performed to validate the model and to predict creep parameters under different temperature and stress loading conditions. Comparing the experimental data with simulation results, we found that the proposed CP model captures creep behaviour in primary, secondary, and tertiary regime for all the lamellar orientations with good accuracy. This model can be further used for investigating microstructure-sensitive creep behaviour of a wide range of TiAl alloys.

Effect of Irradiation with Si+ Ions on Phase Transformations in Ti–Al System during Thermal Annealing

The article deals with the effect of irradiation with Si+ ions on phase transformations in the Ti–Al system during thermal annealing. An aluminum film with a thickness of 500 nm was deposited on VT1-00 titanium samples by magnetron sputtering, followed by ion implantation. Samples before and after irradiation with Si ions were annealed in a vacuum of 10−4 Pa in the temperature range 600–1000 °C. It was established that ion implantation reduces the dissolution of Al in α-Ti with the formation of titanium silicides (TiSi2, Ti5Si3) and stabilizes aluminide phases Ti3Al rich in aluminum. As a result, a composite structure based on titanium silicide/aluminide was obtained on the surface of the sample synthesized by complex treatment: deposition, irradiation with Si+, and thermal annealing at the near-surface layers. The formation of the phase-structural state of the implanted layers is associated with the displacement of atoms of the crystal lattice, a result that is reflected in an increase in the size of the crystal lattice and a decrease in microdistortion of the lattice. The opposite effect is observed with increasing temperature. This fact is explained by the relaxation of unstable large grains with an excess of internal energies. At the annealing temperature of 900–1000 °C, a significant increase in microhardness was observed due to silicide phases.

Role of Si on lamellar formation and mechanical response of two SPS Ti–15Al–15Si and Ti–10Al–20Si intermetallic alloys

Two TiAlSi intermetallic compounds produced by Spark Plasma Sintering (SPS) adding different Si content were tested by nanoindentation, toughness and wear resistance. Microstructure differences between the two alloys were characterized by TEM and a strengthening model was proposed. The microstructure-based strengthening model well agreed with alloys stress obtained from the nanoindentation hardness. It resulted that as Si content increases, the TiAl phase started to form lamellar structure and inter-lamellar twinning. Al reduction in favour of an equal amount of Si was found to slightly promote Ti5Si3 silicide formation and eventually a TiAl phase coarsening. Ti–15Al–15Si alloy showed submicrometric equiaxed TiAl grains. On the other hand, Ti–10Al–20Si alloy was characterized by a lamellar TiAl phase which was identified as responsible for the different mechanical responses of the two alloys.

Investigation of the microstructure, mechanical properties and fracture mechanisms of dissimilar friction stir welded aluminium/titanium joints

Dissimilar friction stir lap welded joints of AA6061-T6 and Ti6Al4V were successfully welded using suitable parameters, and the effect of tool rotational speed was studied to investigate the influence on mechanical properties, microstructure, and fracture mechanisms. It was observed that tool rotational speed has a great effect on the strength of the welded joint, as it controls the amount of heat input and plasticity at Al/Ti interface as well as the formation of intermetallic compounds (IMCs) and different brittle phases that were formed at the Al/Ti mixture. The maximum shear strength of 3.5 KN was achieved using low rotational speed of 600 rpm and maximum hardness of 384 HV, while minimum shear strength of 2.5 KN was attained at 1000 rpm with minimum hardness of 343.2 HV. Hybrid fracture surface was produced at lower rotation speed which had both brittle and ductile characteristics, while brittle fracture mechanisms were observed at high rotational speed due to the concentration of brittle IMCs layers, TiAl, and TiAl3 phases at the interface due to the excessive heat input which causes pores and cracks and thus deteriorating joint strength.

Temperature-dependent deformation processes in two-phase TiAl + Ti3Al nano-polycrystalline alloys

Although deformation processes in single-phase nano-polycrystalline alloys at different temperatures are well described, the deformation mechanism in two-phase nano-polycrystalline alloys at different temperatures is still unclear. Here, the deformation behaviour of the two-phase TiAl+Ti3Al nano-polycrystalline alloys is investigated at different temperatures by molecular dynamic simulation. For a comprehensive understanding of the processes, mechanical properties of the single-phase TiAl and Ti3Al nano-polycrystalline alloys are explored as well. The results of numerical simulations indicate that temperature has a strong influence on the deformation mechanism of the alloys. When temperature is below 800 K, the critical grain size (~8.3 nm) becomes a dominant factor controlling the deformation process in the single-phase TiAl. In the two-phase TiAl+Ti3Al nano-polycrystalline alloys, the motion of dislocations in the TiAl phase with the grain size smaller than the critical size dominates the deformation process. On the other hand, no obvious phenomena linked with the critical size occur in the Ti3Al phase. Once the strain exceeds 18.0%, the dislocation emission is observed in the Ti3Al grains. At high temperatures (≥800 K), in the two-phase nano-polycrystalline alloy, the deformation mechanism changes from the plastic deformation to the boundary slip and recrystallization.

Síntesis y caracterización estructural del compuesto de refuerzo de Ti+Ni3Al+Al2O3 a base de Fe producido por aleación mecánica

La mezcla de polvo de Ti+Ni3Al+Al2O3 a base de Fe se alea mecánicamente en un molino de bolas Spex. Los compuestos con adición de Ti+Ni3Al+Al2O3 a base de Fe se produjeron a una temperatura de sinterización de 1000 °C durante un tiempo de 1 h. Las propiedades de estos compuestos se examinaron mediante microscopía electrónica de barrido (SEM), microscopía óptica (OM), espectroscopía de dispersión de energía (EDS), difracción de rayos X (XRD) y análisis de microdureza. El producto final producido por aleación mecánica fue una solución sólida rica en níquel nanocristalina, el tamaño promedio del cristal era de unos pocos nanómetros. El contenido de titanio en el refuerzo aumentó los valores de microdureza del composite. Los compuestos producidos incluían las fases Fe3Al, TiAl, NiAl, Al3Ni2, Al2O3 y Fe3O.

Investigation on Ultrasonic Cavitation Erosion Behaviors of Al and Al-5Ti Alloys in the Distilled Water

Al and Al-5Ti alloys were manufactured by an ultrasonic casting method with a new device, and their ultrasonic cavitation erosion behaviors of Al and Al-5Ti alloys in the distilled water were clarified. The damage mechanism was analyzed by macro photograph, scanning electronic micrograph and three-dimensional morphology, and the results demonstrate that Al-5Ti alloys have better cavitation erosion resistance than Al in terms of the mass loss and the surface damage. The deformation mechanism of Al and Al-5Ti alloys under cavitation erosion is mainly dislocation slip, and the Al3Ti phase enhances the cavitation erosion resistance of Al-5Ti alloys. In addition, the maximum depth of cavitation pits in the Al-5Ti sample is less than that in the Al sample for 31.3%.

Effect of Al–Si alloy coating on interfacial reactions and tensile strength in Ti/Al dissimilar brazing joints

Abstract We used ultrasonic-assisted brazing to join Al-Si-coated Ti alloys and Al alloys with a Zn-Al-Si filler metal. At the interface between the Ti alloy and Al-0.1Si alloy coating, a block TiAl3 phase formed. In contrast, for the Al-5Si alloy coating, the interfacial reaction layer of the joint consisted of a block Ti(Al,Si)3 phase and needle-like Ti7Al5Si12 phase. Finally, a granular Ti7Al5Si12 phase was formed at the joint interface for the Al-12Si alloy coating. The tensile strength of the joints formed with the Al-0.1Si and Al-12Si alloy coatings was only 160 -185 MPa, and cracks propagated mainly through the reaction layer. The tensile strength of the joints formed with the Al-5Si alloy coating ranged from 210 to 215 MPa, and cracks appeared entirely within the coating, subsequently expanding along the coating and ultimately resulting in failure of the joint.

Mechanical properties, corrosion behavior and biocompatibility of orthopedic pure titanium−magnesium alloy screw prepared by friction welding

Abstract The dissimilar joining of biodegradable magnesium alloy to pure commercial titanium by rotational friction welding with rotational speeds of 1100, 1200 and 1300 r/min for the production of bio-screw was investigated. The metallographic analysis revealed that a good joining was obtained at the Ti/Mg alloy joint. On the magnesium alloy side, various regions such as the weld center zone (WCZ), dynamic recrystallization zone (DRX), thermo-mechanically affected zone (TMAZ) and partially deformed zone (PDZ) were observed. The highest tensile and shear strengths were 173 and 103.2 MPa, respectively at a rotational speed of 1300 r/min. The Ti/Mg alloy dissimilar friction welded joint failed at the vicinity of the intermetallic zone containing Ti3Al phase. The hardness values from the base metal magnesium alloy to the joining point increased mainly due to grain refinement (8.57 μm in diameter) and the presence of titanium particles, while the hardness values were constant on the titanium side. It was also found that the corrosion rate of the Ti/Mg alloy joint was higher compared with that of the Ti and Mg alloy from the immersion studies. Additionally, the sample with a rotational speed of 1300 r/min showed better biocompatibility and a cell viability of 98.12% due to better corrosion resistance.

Interfacial microstructure and tensile strength of TiAl joint brazed with an improved Ti-Zr-Cu-Ni filler

Ti-16.5Zr-13.5Cu-8.5Ni (wt.%) as a filler and brazing process as 950 °C/60 min were supplied in this study for brazing cast TiAl alloys with fully lamella structure. The interface microstructure and element diffusion were analyzed and measured by SEM, EBSD, and EPAM. And the mechanical properties of joints were evaluated. The sound joints were achieved with strength as 575 MPa at room temperature and remained as 410 MPa and 385 MPa in average at 700 °C and 760 °C, respectively. It was attributed to lots of fine grains with soft orientation as BCC [120] in the joint to the tensile direction. It was found that the fracture happened in the local zones with very large grains and the extreme misorientation between grains in the joint. Even though most grains as Ti3Al phase were found in the joint, there was no sign indicating the formed IMC related to the fracture.

High-Temperature Oxidation Behavior of Al-Modified Boronized Coating Prepared on Ti-6Al-4V by Thermal Diffusion

The Al-modified boronized coating on Ti-6Al-4V was successfully fabricated to protect the alloy from oxidation by the neutral salt bath method. The thickness of the Al-modified boronized coating (69.8 ± 2 μm) is 36% thicker than that of the simple-boronized coating (51.3 ± 1.5 μm). To evaluate the oxidation resistance, the high-temperature oxidation behavior was analyzed by the high-temperature oxidation experiment at 700 and 900 °C. The results show that after oxidation, the Al-modified boronized coating was mainly comprised of TiO2, Al2O3, Al3Ti, Ti3B4 and TiS phases, and the surface of the Al-modified boronized coating is smoother and denser. The thickness of the oxide layer of the Al-modified boronized coating is the minimum, which is 11 ± 0.3 μm and 13 ± 0.5 μm at 700 and 900 °C for 60 h, respectively. The average oxidation rate of the Al-modified boronized coating is − 0.003 and 0.022 mg cm−2 h−1 due to the formation of Al2O3 on the surface. Therefore, adding Al into the simple-boronized coating is beneficial for the high-temperature oxidation resistance.

Mechanical Properties of Microlayered Ti–Al Materials in Static and Cyclic Loading

The technique for producing microlayered materials by sintering and rolling a package of alternating titanium and aluminum ribbons at 460 and 770°C is presented. The initial package thickness was 2.6 mm and the final thickness after hot rolling was 1.8 mm. Then the preform was rolled at room temperature to a thickness of 0.5 mm. The total strain at 20°C was e = ln1.8/0.5 = 1.3. Some ribbons 0.5 mm thick stratified in the middle and were tested by static and cyclic bending. X-ray diffraction found that the material that was heated and rolled at 770°C contained an hcp titanium phase and a TiAl3 phase. Structural anisotropy in titanium layers was established. The proportional limit of the 0.5 mm thick material was 368 MPa. The elastic characteristics, transmission energy of vibrations, and fatigue strength of the microlayered Ti–TiAl3 samples 0.25 mm thick cut along and across the rolling direction were determined. For this purpose, firstand second-mode resonant bending vibrations of cantilevered samples were excited and dependences of the maximum stresses in the samples on machine (electrodynamic shaker) power, W/Wmax, were found. The destructive fatigue stresses in the samples versus the number of load cycles were determined as well. Young’s modulus of the samples cut out along the rolling direction was 92 and for the samples cut out across the rolling direction was 100 GPa. The microlayered Ti–TiAl3 material along the rolling direction is less perfect than that across the rolling direction since nondestructive stresses are 11% lower along the rolling direction because of greater energy dissipation in anisotropic crystallographic structure, the relative excitation power of vibrations being the same. The ultimate strength determined from 107 cycles (Troll = 460°C) was 303 MPa for the Ti–Al samples along the rolling direction and 299 MPa for the Ti–TiAl3 samples along the rolling direction and 481 MPa for those across the rolling direction.

Effects of annealing on the interface microstructures and mechanical properties of hot roll bonded Ti6Al4V/AA6061 clad sheets

In this study, Ti6Al4V/AA6061 clad sheets were successfully obtained via hot roll bonding. The effects of annealing on the interface microstructures and mechanical properties of the clad sheets were investigated. The interface microstructures were observed via scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Tensile tests were conducted to investigate the mechanical properties of the clad sheets. The results demonstrated that the TiAl3 phase formed in the Ti/Al interface when the annealed temperature was above 550 °C. The Al atoms were the dominant diffusing atoms through the TiAl3 layer and reacted with Ti atoms at the Ti/TiAl3 interface. A thin layer including MgAl2O4 and unreacted Al was observed in the TiAl3 zone near the Al side. The thickness growth of the TiAl3 layer was dominated by linear growth. After annealing treatment, the tensile strength of the clad sheets initially decreased from the as-rolled to 400 °C annealed samples, subsequently increased with annealing temperature from 400−550 °C, and then finally decreased. The strength of the clad sheets was in good agreement with the calculated value from the rule of mixture. The ductility increased with increasing annealing temperature, reaching its maximum value at 550 °C, and then subsequently decreased at 600 °C.