Ti2AlNb Alloy Research Articles

Effects of PVD CrAlN/(CrAlB)N/CrAlN Coating on Pin–Disc Friction Properties of Ti2AlNb Alloys Compared to WC/Co Carbide at Evaluated Temperatures

Physical vapor deposition (PVD) coatings could affect the friction performance at the contact interface between Ti2AlNb alloy parts and tool couples. Suitable coating types could improve the friction properties of Ti2AlNb alloy while in contact with WC/Co carbide. In this study, the linear reciprocating pin–disc friction tests between the Ti2AlNb alloy and the WC/Co carbide tool couple, with the sole variation of the PVD CrAlN/(CrAlB)N/CrAlN coating were conducted within the temperature range of 25–600 °C. The antifriction properties of the Ti2AlNb alloy were estimated using the time-varied friction coefficients, the alloy wear rate, worn surface topography, worn surface element, and wear mechanism analysis. The results showed that the PVD CrAlN/(CrAlB)N/CrAlN coating could decrease the average friction coefficient and alloy wear rate compared to the uncoated WC/Co carbide couple. The apparent adhesive wear and abrasive wear of the Ti2AlNb alloy could be improved due to the PVD coating at evaluated temperatures. The PVD CrAlN/(CrAlB)N/CrAlN coating could be utilized to improve the antifriction properties of the Ti2AlNb alloy, which may be deposited on the cutting tool to improve the machining performance of Ti2AlNb alloys in future aerospace machining industry.

Enhanced fracture toughness of Ti2AlNb/Ti6Al4V layered metal composite

Drawing inspiration from the intricacies of nacre structure, Ti2AlNb/Ti6Al4V layered metal composite was fabricated by vacuum hot pressing and achieved high fracture toughness. The fracture toughness of the composite registers at 48.5 MPa∙m1/2, surpassing the theoretical fracture toughness calculated based on the rule of mixture (ROM) and exhibiting 54 % improvement compared toTi2AlNb alloy. The introduction of a layered configuration imparts complex crack propagation pathways to the composite. The occurrences of crack deflection, crack bridging, crack passivation, and interface delamination serve to increase the resistance to crack propagation. Moreover, the plastic deformation of the ductile Ti6Al4V layer and the large plastic zone size of the crack tip can release the stress concentration and delay the fracture of the composite. This understanding not only advances our comprehension of the toughening mechanisms but also has practical implications for the application and development of layered Ti2AlNb alloys.

Dynamic Mechanical Properties and Modified Material Constitutive Model for Hot Forged Ti2AlNb over Wide Ranges of Temperature and Strain Rate.

In this paper, the stress-strain curves of Ti2AlNb are established based on uniaxial impact tests over wide ranges of temperature and strain rate. The Ti2AlNb exhibited the work hardening effect but did not show an obvious yield stage during a quasi-static compression test. In the SHPB test, an obvious temperature softening effect was found, the strain rate strengthening effect was detected when the strain rate was 4000-8000 s-1, and the strain rate softening effect was detected in the range of 8000-12,000 s-1. A function describing the effect of strain rate on the strain rate strengthening parameters under various temperatures was proposed to modify the basic J-C constitutive model. The relative errors between the experimental measured value and predicted values in various experimental conditions with a modified J-C model were less than 5.0%. The results verified that the modified J-C model could accurately describe the dynamic mechanical properties of Ti2AlNb at high temperatures and strain rates. The research could help to illustrate the cutting mechanism and finite element simulation of Ti2AlNb alloy.

High-temperature oxidation behavior of double glow plasma Cr-Y alloyed layers on Ti2AlNb alloy

A Cr-Y alloyed layer was synthesized on the surface of Ti2AlNb by double glow plasma surface alloying technique. The morphology, phase composition and oxidation behaviors at 750 °C, 800 °C, and 850 °C of Cr-Y alloyed layers were systematically investigated. The results illustrated that Cr-Y alloyed layer was approximately 10 μm thick, which the morphology of alloyed layer was uniform and compact, with a flat and uniform interface to the matrix. Oxidation kinetics for the Cr-Y alloyed layer approximately followed the parabolic law, with an oxidation weight gain significantly lower than that of Ti2AlNb. The predominant oxides of Cr-Y layer were CrNbO4, Cr2O3, and Y2O3, which effectively hindered oxygen diffusion into the substrate.

Exploiting top ductile B2/β layers to in-situ cold-forging Ti–22Al–25Nb alloy manufactured by laser melting deposition

Ti–22Al–25Nb intermetallic alloy is the latest generation of lightweight aerospace material with superior high-temperature performance. In the present study, a novel hybrid 3D-printing technique, point-forging and laser-deposition (PF-LD), was adopted for demonstrating its possibility in the preparation of near-net-shaping Ti–22Al–25Nb component. We innovatively exploited the top ductile B2/β-phase-zone as a natural protective layer, successfully preparing Ti–22Al–25Nb intermetallic parts with relatively larger build-height without initiating any macro-micro cracks. Three groups of control trials were further performed to ascertain the effect of initial laser parameters on microstructural characteristic and mechanical performance. Among three deposition strategies, the sample with intermediate laser scanning rate reached the best combination of ultimate tensile strength (UTS: ∼ 1280.7 MPa) and elongation after failure (EL: ∼ 5.7 %), while superior tensile strength (UTS: ∼ 1314.8 MPa) could be also achieved at the expense of tensile ductility (EL: ∼ 2.4 %). This study not only reveals a new idea to low-temperature forming Ti–22Al–25Nb alloy, but also provides an insight into the relationship between PF-LD processing parameters and mechanical performance.

Microstructure evolution and property strengthening of Ti2AlNb alloys prepared by multi-wire arc-directed energy deposition

Ti2AlNb alloys are expected to have applications in the aerospace field because of their excellent high-temperature performance and moderate density. Multi-wire arc-directed energy deposition (MWA-DED) technology enables the in-situ formation of Ti2AlNb alloys. However, Ti2AlNb alloys fabricated by MWA-DED face challenges such as compositional segregation and poor mechanical properties. In this study, high-performance Ti2AlNb alloys were efficiently prepared using MWA-DED technology, and their microstructure evolution was systematically analyzed. Hot-wire technology was proposed to assist in melting the TiNb wire to minimize the difference in the physical properties of the two wires. A pre-alloy droplet transfer mode with a large arc length was developed to eliminate composition segregation. The results showed that the Ti2AlNb alloys exhibited a homogeneous composition that matched the target Ti-22Al-23 Nb. Lots of strengthening phases (O phases higher than 90%) were precipitated throughout the sample. Temperature fields calculated from finite element simulation revealed that the precipitated phases were attributed to the “in-situ” heat treatment during deposition. The ultimate tensile strength and elongation reached 1002 MPa and 8% at room temperature, and 756 MPa and 8.3% at high temperature (650 ℃), respectively. The outstanding mechanical properties of Ti2AlNb alloys fabricated by MWA-DED are superior to those of cast and previously reported additively manufactured alloys. This study proposes novel ideas for additive manufacturing of high-performance Ti2AlNb alloys.

Hot pack rolling the Ti2AlNb alloy prepared by SPS: Testing of the high-temperature properties of the alloy directly without the prior heat treatment

Ti2AlNb alloy holds large research significance as a lightweight material for high-temperature structural applications in the next generation of aero-engines. In this work, pre-alloyed Ti2AlNb powders were spark plasma sintered to fabricate the raw compact, which was then hot rolled at different phase fields to fabricate sheets. The high-temperature properties of the sheets were tested directly without the prior heat treatment. Results show that the Ti2AlNb sheets have good high-temperature strengths even without the heat treatment prior to testing. For the sheet rolled at the single B2 phase region, the maximum tensile strength was up to 931.4 MPa at 650 °C. The sheet mainly shows intergranular fracture mode due to the weak bonding at grain boundaries. The sheets rolled at the O + B2 phase region have low tensile strengths at different testing temperatures. For the sheet rolled at α2+O + B2 phase region, the tensile strength gains its maximum strength of 956.6 MPa at 650 °C, and the sheet shows transcrystalline fracture mode. The fracture mechanisms of the sheets rolled at different phase regions are analyzed in detail and proved by experiment. This work shows the potential of fabricating Ti2AlNb sheet by using the spark plasma sintered compact.

Construction of a Triboelectrochemical Setup with Controlled Environment for Biomaterial Testing with a Comparison of Cobalt–Chromium–Molybdenum and Titanium–Aluminium–Niobium Alloys

The present work is focused on the manufacturing of a special self‐developed tribocorrosion setup with a controlled incubated environment. The comparative studies between wrought Co27Cr6Mo and Ti6Al7Nb alloys are performed with the respective tribometer in Ringer's solution at 37 °C. It is found that the CoCrMo alloy demonstrated a noble open circuit potential not only in non‐wear condition but also under wear conditions, in comparison to Ti6Al7Nb. The mass loss rate examined at open circuit potential and at a constant potential of 0.2 V versus Ag|AgCl|3.5 m KCl also suggests a similar superiority of the CoCrMo alloy.

A novel insight of solid–liquid interaction effect during laser hybrid manufacturing Ti2AlNb alloy

Combining interlayer point-forging with laser-deposition (PF-LD) provides a new idea to in-situ modify coarse-grained structure and strong solidification texture during high-thermal additive manufacturing process. In this study, a well-designed step-experiment with one to three-pass PF-LD was conducted on columnar-grained Ti2AlNb substrate to elucidate a novel insight of solid–liquid interaction effect. The results revealed that the combination of localized micro-forging and laser re-heating was capable to produce randomly-distributed equiaxial structure via interlayer recrystallization behavior, at the same time it in turn had a positive effect on solidification grain refinement. The essential contribution of these fine-grained microstructures further created an acceleration effect to interlayer recrystallization behavior and promoted the full-equiaxial grain morphology of PF-LD Ti2AlNb part.

Effect of Preheating and Post-Heating on the Microstructures and Mechanical Properties of TC17-Ti2AlNb Joint with Electron Beam Welding.

To enhance welding quality and performance, preheating and post-heating are usually employed on high-temperature materials, concurrently with welding. This is a novel technique in vacuum chamber electron beam welding (EBW). TC17 and Ti2AlNb alloys are the hot topics in aero-engine parts, and the welding of dissimilar materials is also a broad prospect. To settle welding cracks of Ti2AlNb, EBW with preheating and post-heating was investigated on TC17 and Ti2AlNb dissimilar alloy, which improved the manufacturing technology on high-temperature materials. The dissimilar joint no longer had cracks after preheating, which exhibited excellent welding stability and metallurgical homogeneity, and preheating and annealing had an important effect on mechanical properties. The joint strength after 630 °C annealing is higher than that of TC17 alloy base metal (BM) and other annealing temperatures, reaching 1169 MPa at room temperature and 894 MPa at 450 °C tensile condition. The joint plasticity after 740 °C annealing is equivalent to TC17 BM. EBW with preheating improved the microstructure characteristics and enhanced the plasticity of Ti2AlNb alloy weld and dissimilar joint, which would contribute to the application of Ti2AlNb alloy and Ti2AlNb dissimilar parts.

Formation of heterogeneous interfaces in the TiAl/Ti2AlNb layered composite and its effect on the fracture toughness

TiAl/Ti2AlNb intermetallic-intermetallic laminated (IIL) composites featuring brittle/ductile heterogeneous interfaces were fabricated through vacuum hot-pack rolling. The microstructures and the phase transformation behaviors of the interfaces of the IIL composites before and after annealing at 900 °C/6 h were investigated. The heterogeneous interfaces are composed of four distinct regions, individually I (βo+γ+α2), II (βo/B2+ω) (brittle part), III (O lath), and IV (equiaxed O) (ductile part) regions from TiAl to Ti2AlNb side. Notably, after annealing, an equiaxed O band approximately 50 μm wide was observed in region IV of the interface. In addition, a significant microhardness variation was observed between regions II and IV of the interface, where region II exhibited higher hardness compared to the TiAl alloy, and region IV displayed lower hardness than the Ti2AlNb alloy. The enhanced fracture toughness of the IIL composites, three times that of the TiAl base alloy, is attributed to the formation of the brittle/ductile heterogeneous interfaces and the layered design incorporating the Ti2AlNb alloy. The corresponding toughening mechanism was further discussed. The brittle II region plays a role in increasing crack branching, while the ductile IV region inhibits the propagation of microcracks and prevents the formation of main cracks. This work highlights the crucial role of the brittle/ductile heterogeneous interface in the toughening of laminated composites. Furthermore, the discovery of the O band provides novel insights into the design of TiAl/Ti2AlNb heterostructures.

A Comprehensive Investigation on Nanomechanical, Scratch, and Tribological Characteristics of TaN-Ag Nanocomposite Coating on Ti6Al7Nb Alloy

A Comprehensive Investigation on Nanomechanical, Scratch, and Tribological Characteristics of TaN-Ag Nanocomposite Coating on Ti6Al7Nb Alloy

Synergistic effect of B2 phase and O phase in hot-rolled Ti2AlNb alloy and its influences on mechanical properties

The Ti2AlNb alloy, solution-treated at 1070 °C, underwent hot rolling at 960 °C with different thickness reductions to investigate the synergistic effects of the O phase and B2 phase and their impact on its properties. The results reveal that after solution treatment, the Ti2AlNb alloy consists of nearly spherical O, lath O, and B2 matrix at 30% and 50% thickness reductions during hot rolling. However, at a 70% thickness reduction, the alloy exhibits spherical O, worm-like O, and a continuously distributed B2 phase. The α2 phase formed during solution treatment decomposes during hot rolling. As the thickness reduction increases from 30% to 70%, the O phase content initially rises and then declines, accompanied by an increase in the average dimension of the O phase from 0.25 ± 0.16 μm to 0.36 ± 0.18 μm. Additionally, the B2 phase in the alloy undergoes dynamic recrystallization (DRX) during hot rolling, coinciding with the growth and spheroidization of the O phase. With an increase in the thickness reduction during hot rolling, the elongation of the alloy increases from 5.9% at 30% reduction to 12.47% at 70% reduction. Meanwhile, the ultimate tensile strength reaches its peak value of 1092.2 MPa at 30% reduction, decreases to 936 MPa at 50%, and then increases to 970 MPa at 70%. The tensile strength of the alloy improves due to the interaction and accumulation of dislocations at the phase interface. The continuous distribution of the B2 matrix, dislocation movement, rotation of the O phase, DRX of the B2 phase, and interface slip all contribute to enhanced ductility. Furthermore, the fracture behavior of the Ti2AlNb alloys under various hot rolling conditions was elucidated.

Effect of electric current on microstructure and texture evolution of the Ti2AlNb alloy during hot deformation

In this study, the stress-strain behavior of sintered Ti2AlNb alloy obtained at the temperatures of 980 °C and 1080 °C with a strain rate of 0.5 s−1 was investigated using compression tests under furnace heating and current heating. When deformed at 980 °C, the B2 phase texture orientation all exhibited <001>//ND and <101>//ND during current-assisted hot compression (CAHC) and furnace hot compression (FHC). With the deformation temperature increased to 1080 °C, the texture <001>//ND gradually moved towards the <111> texture direction during CAHC. The results were ascribed to the different microstructure evolution that dynamic globularization and DRX by electric current. It indicated that the current promoted the spheroidization of the O phase which did not change the texture orientation. However, as the temperature increased to 1080 °C, the current promoted dynamic recrystallization which resulted in big changes in B2 phase texture orientation. The current promoted the spheroidization of lath by accelerating the phase transformation of O→B2. The current affected the dynamic recrystallization (DRX) mechanisms by promoting the transformation of low-angle grain boundaries (LAGBs) into high-angle grain boundaries (HAGBs) through continuous absorption of dislocations. The true stain-stress curves indicated the reduction of the deformation resistance and enhancement of the deformability of the Ti2AlNb alloy, which was closely related to the microstructure evolution.

Effects of solid solution and aging treatment on the microstructure evolution of Ti2AlNb alloy

The effects of solid solution temperature, aging temperature and aging cooling rate on the microstructure evolution of forged Ti-22.5Al-24.7Nb (at. %) alloy were investigated. With the increasing solid solution temperature, the number of equiaxed microstructure first increases and then decreases, reaching the maximum at 900 °C. Lamellar microstructure solubilizes in the matrix or gradually becomes coarser and shorter, and transforms into equiaxed microstructure. When the solution temperature is 1000 °C, equiaxed α2 phase gradually changes to be lath-shaped and concave. During the aging process, some α2 phase transforms into O phase, and the aging temperature affects the shape of equiaxed microstructure and the spacing between the needle-like microstructure. With the increasing aging temperature, the number of equiaxed microstructure increases linearly, and the proportion of fine secondary O phase decreases while the thickness increases. The lamellar morphology of O phase can be retained at a faster cooling rate, while a portion of lamellar O phase is converted to the B2 phase after furnace cooling. Through heat treatment, the volume fraction and the size of lamellar O phase could be well controlled.

Microstructure evolution of TC25G/Ti2AlNb structural gradient material fabricated by laser directed energy deposition

Laser directed energy deposition (LDED) is one of the most effective ways to manufacture structural gradient materials. The microstructure changes in transition zone (TZ) and heat-affected zone (HAZ) are often considered to be very important which could affect the mechanical property of the component. In this study, a titanium based gradient material, which is potentially used in high pressure compressor was fabricated by deposition of Ti2AlNb alloy on a forged TC25G alloy substrate. The thickness of the transition zone is around 2000 μm, and the phase transformation from TC25G alloy to Ti2AlNb alloy is followed as: α + β (TC25G alloy) → α + β (Heat affected zone) → α + α2 + B2/β + O (Transition zone) → α2 + B2/β + O (Ti2AlNb alloy). There is no any sudden change of microhardness in the gradient material with the lowest microhardness is found in Ti2AlNb alloy.

Structural and High-Temperature Oxidation Performance of Al-Co-Y Co-deposited Coatings on a TiAl-Nb Alloy at Low Temperatures

Structural and High-Temperature Oxidation Performance of Al-Co-Y Co-deposited Coatings on a TiAl-Nb Alloy at Low Temperatures

First-Principles Investigation on the Adsorption and Diffusion of Oxygen at the B2(110)–O(001) Interface in Ti2AlNb Alloys

The adsorption and diffusion of oxygen at the B2(110)[1¯11]||O(001)[11¯0] interface in Ti2AlNb alloys were investigated via first-principles calculations. Only a 2.6% interfacial mismatch indicates that B2(110)–O(001) is basically a stable coherent interface. The calculated adsorption energies and diffusion energy barriers show that oxygen prefers to occupy the Ti-rich interstitial sites, and once trapped, it hardly diffuses to other interstitial sites, thus promoting the preferential formation of Ti oxides. Under the premise of a Ti-rich environment, a Nb-rich environment is more favorable for oxygen adsorption than an Al-rich environment. The electronic structures suggest that O 2p orbitals mainly occupy the energy region below −5 eV, bonding with its coordinated atoms of Ti, Al, and Nb. However, Al 3p and Nb 4d orbitals near the Fermi level couple with sparsely distributed O 2p orbitals, forming anti-bonding, which is not conducive to oxygen adsorption. Because Nb 4d electrons are more localized than Al 3p electrons are, Nb–O anti-bonding is weaker. O–Ti has almost no contribution to anti-bonding, suggesting good bonding between them. This is consistent with the experimental observations that TiO2 is the main oxidation product.

Investigation on creep behavior and microstructural features of an additively manufactured Ti2AlNb alloy upon isothermal deformation at elevated temperature

In this work, we investigated the creep behavior of a SLM-printed Ti2AlNb alloy and systematically examined the corresponding microstructural features using multi-scale characterization methods. A single β-phase matrix is produced in the alloy due to the extremely fast solidification process. A new O phase transformation is triggered by the applied external stress following the crystallographic relation of (101) B2//(001) O, compared with the aged counterpart in which only the conventional β-to-O phase transformation with a (110) B2//(020) O relation occurs. This phase transformation contributes to improving the creep resistance of printed specimen test applied with creep stress of 150 MPa at 923 K, suggesting a final steady strain rate of ∼5 × 10–8/s. This work further elucidates the mechanisms of the microstructural evolution of SLM-printed Ti2AlNb-based alloys on creep and offers valuable insights for the future development of high creep-resistance alloys.

Effect of sintering temperature on microstructure and mechanical properties of Ti2AlNb-based composites

Ti2AlNb-based composites are a great choice for achieving high-temperature properties by introducing reinforcement to meet engineering application requirements. In this study, Ti–22Al–25Nb (at.%) alloys and nano-Al2O3/Ti–22Al–25Nb composites were prepared by mechanical alloying (MA) and hot pressing (HP). The effects of sintering temperature on the microstructure and mechanical properties of Ti–22Al–25Nb alloys and Ti2AlNb-based composites were investigated. The sintering temperature effectively regulated the morphology and size of the primary O phase. The addition of Al2O3 particles refined the grain size of the matrix and precipitates, and it induced the phase transformation. When the sintering temperature reached 1350 °C, Ti–22Al–25Nb alloys and Ti2AlNb-based composites obtained a fine and uniform equiaxed microstructure. The hardness and ultimate compressive strength of the composite first increased and then decreased with increasing sintering temperature. Since the addition of Al2O3 particles promoted the precipitation of the ultrafine acicular O phase from the B2 phase, the composite sintered at 1350 °C had the optimal mechanical properties. The hardness of the Ti–22Al–25Nb alloy and Ti2AlNb-based composite was 4.12 GPa and 5.1 GPa, respectively. The ultimate compressive strength of the composite at room temperature (RT) and 650 °C was 2642.3 MPa and 2462.5 MPa, which was 25.8% and 9.6% higher than that of the Ti2AlNb alloy. The strengthening mechanism of the composites mainly includes dispersion strengthening and Orowan strengthening of the nano-Al2O3 particles, as well as precipitation strengthening of the acicular O phase. This study provides a theoretical guidance for designing Ti2AlNb-based composites with excellent high-temperature properties.