Ti2AlNb Alloy Research Articles

Thermodynamic Study on Initial Oxidation Behavior of TiAl-Nb Alloys at High Temperature

The initial oxidation behavior of TiAl-Nb alloys was systematically investigated against the composition, temperature, and partial pressure of O2 with the CALculation of PHAse Diagrams (CALPHAD) technique. The mole fraction of each oxidation product at the initial oxidation stage of the alloys at the corresponding temperatures was predicted. The initial oxidation products of the alloys are oxides of Al, Ti, and Nb, with the oxidation order of Al, Ti, and Nb. As P(O2) increases, the Ti and Nb oxidation products move towards a high oxygen content, and the mole fractions of the Al and Ti oxides gradually decrease and increase, respectively. It was found that the temperature and partial pressure of O2 determined the types of the oxides and the oxidation order, while the concentration of Nb and Al determined the mole fraction of the oxides. The CALPHAD results are in good agreement with the experiments.

Effect of Laser Treatment on Surface and Interface of Silicon Nitride Coated Ti6Al7Nb Alloy – A Statistical Analysis

Effect of Laser Treatment on Surface and Interface of Silicon Nitride Coated Ti6Al7Nb Alloy – A Statistical Analysis

Surface modification of Ti6Al7Nb alloy by Al2O3 nanofilms and calcium phosphate coatings

Here we have modified Ti6Al7Nb alloy by Al2O3 using Atomic Layer Deposition (ALD) and apatite coating electrodeposited and by Simulated Body Fluid method. X-Ray Fluorescence (FRX), Energy Scattering X-Ray Spectroscopy (EDS), Scanning Electron Microscopy (SEM), X-Ray Diffraction Spectroscopy (XRD), Raman Spectroscopy and Force Microscopy Atomic (AFM) revealed the chemical and crystallographic composition of Ti6Al7Nb before and after surface modifications. A laminar apatite crystal in the form of plates and irregular crystals, with the appearance of flakes growing from the center to the edge and resembling flowers were produced closed to synthetic apatite's. In vitro biological tests showed that surface modifications in the titanium alloy Ti6Al7Nb improved the bioactivity attributed to the formation of microporosity favorable to the greater production of total proteins and, also, influenced the nucleation of apatite's at the nanoscale. The results presented here confirmed the non-cytotoxicity, strongly supporting the application of these nanofilms in tissue engineering.

Microstructural Evolution and Mechanical Properties of Ti2AlNb/GH99 Superalloy Brazed Joints Using TiZrCuNi Amorphous Filler Alloy

Dissimilar materials brazing of Ti2AlNb alloy to GH99 superalloy is of great pragmatic importance in the aerospace field, especially the lightweight space aircraft components manufacturing. In this work, TiZrCuNi amorphous filler alloy was used as brazing filler, and experiments were carried out at different brazing temperatures and times to investigate the changes in interfacial structures and properties of the joints. The typical interfacial microstructure was Ti2AlNb alloy/B2/β/Ti2Ni (Al, Nb) + B2/β + (Ti, Zr)2(Ni, Cu) + (Ti, Zr)(Ni, Cu)/(Cr, Ni, Ti) solid solution + (Ni, Cr) solid solution/GH99 superalloy when being brazed at 1000 °C for 8 min. The interfacial microstructure of the joints was influenced by diffusion and reaction between the filler alloy and the parent metal. The prolongation of brazing process parameters accelerated the diffusion and reaction of the liquid brazing alloy into both parent metals, which eventually led to the aggregation of (Ti, Zr)2(Ni, Cu) brittle phase and increased thickness of Ti2Ni (Al, Nb) layer. According to fracture analyses, cracks began in the Ti2Ni (Al, Nb) phase and spread with it as well as the (Ti, Zr)2(Ni, Cu) phase. The joints that were brazed at 1000 °C for 8 min had a maximum shear strength of ~216.2 MPa. Furthermore, increasing the brazing temperature or extending the holding time decreased the shear strength due to the coarse Ti2Ni (Al, Nb) phase and the continuous (Ti, Zr)2(Ni, Cu) phase.

Crystal Plasticity Finite Element Modeling on High Temperature Low Cycle Fatigue of Ti2AlNb Alloy

Ti2AlNb alloy is a three-phase alloy, which consists of O phase, β phase and α2 phase. Because of the difference in the mechanical characteristics between phases, Ti2AlNb alloy often exhibits deformation heterogeneity. Based on EBSD images of the Ti2AlNb alloy, a crystal plasticity finite element model (CPFEM) was built to study the effects of O phase and β phase (dominant phases) on stress and strain distribution. Four types of fatigue experiments, and the Chaboche model with 1.2%~1.6% total strain range were conducted to verify the CPFEM. The simulation results showed that the phase boundary was the important position of stress concentration. The main reason for the stress concentration was the inconsistency deformation of grains which resulted from the different deformation abilities of the O and β phases.

Mechanism of grain refinement and mechanical property enhancement of Ti-45Al-8Nb alloy by directed laser deposition

Directed laser deposition (DLD) as an important additive manufacturing process, has a good application prospect for the fabricating of complex high Nb-TiAl alloy parts in aerospace and energy industries. The mechanical properties of parts manufactured by DLD are affected by the interlamellar spacing of precipitated phases. In this paper, Ti-45Al-8Nb alloy specimens were manufactured by DLD, and the interactions between the semi-coherent interfaces, deformation twins, and dislocations were analyzed by transmission electron microscopy (TEM), it revealed the strengthening mechanism of interlamellar spacing on mechanical properties of Ti-45Al-8Nb alloy. The results indicate that the laser power is one of the important factors affecting the interlamellar spacing, and the microstructures of the specimens are composed of α2 phase, γ phase, and B2 phase. By the laser power adjusting, the interlamellar spacing λ decreases by 40.1%, the microhardness of the alloy was increased by 15.9%, and the tensile strength increased by 14.8%. Also, the relationship between the tensile strength σb and the interlamellar spacing λ satisfies the Hall-Petch relationship: σb=161.4+3204λ−1/2. The obstruction and absorption of dislocation motion by the lamellar interface and deformation twins are the main reasons for the improved mechanical properties of the alloy.

Corrosion Characteristic and Surface Effect of a Novel Tial-Nb Alloy in Liquid Zinc

Corrosion Characteristic and Surface Effect of a Novel Tial-Nb Alloy in Liquid Zinc

Numerical Simulation of Low Cycle Fatigue Behavior of Ti2AlNb Alloy Subcomponents

Many titanium alloy subcomponents are subjected to fatigue loading in aerospace engineering, resulting in fatigue failure. The fatigue behavior of Ti2AlNb alloy subcomponents was investigated based on the Seeger fatigue life theory and the improved Lemaitre damage evolution theory. Firstly, the finite element models of the standard openhole specimen and Y-section subcomponents have been established by ABAQUS. The damage model parameters were determined by fatigue tests, and the reliability of fatigue life simulation results of the Ti2AlNb alloy standard open-hole specimen was verified. Meanwhile, the fatigue life of Ti2AlNb alloy Y-section subcomponents was predicted. Under the same initial conditions, the average error of fatigue life predicted by two different models was 20.6%. Finally, the effects of loading amplitude, temperature, and Y-interface angle on fatigue properties of Ti2AlNb Y-section subcomponents were investigated. These results provide a new idea for evaluating the fatigue life of various Ti2AlNb alloy subcomponents.

Experimental investigation and optimization of hybrid turning of Ti6Al7Nb alloy under nanofluid based MQL by TOPSIS method

Experimental investigation and optimization of hybrid turning of Ti6Al7Nb alloy under nanofluid based MQL by TOPSIS method

Semi-Quantitative Method of Assessing the Thrombogenicity of Biomaterials Intended for Long-Term Blood Contact

Biomaterials used in cardiosurgical implants and artificial valves that have long-term contact with blood pose a great challenge for researchers due to the induction of thrombogenicity. So far, the assessment of the thrombogenicity of biomaterials has been performed with the use of highly subjective descriptive methods, which has made it impossible to compare the results of various experiments. The aim of this paper was to present a new semi-quantitative method of thrombogenicity assessment based on scanning electron microscope (SEM) images of an adhered biological material deposited on the surfaces of prepared samples. The following biomaterials were used to develop the proposed method: Bionate 55D polyurethane, polyether-ether ketone, Ti6Al7Nb alloy, sintered yttria-stabilized zirconium oxide (ZrO2 + Y2O3), collagen-coated glass, and bacterial cellulose. The samples were prepared by incubating the biomaterials with platelet-rich plasma. In order to quantify the thrombogenic properties of the biomaterials, a TR parameter based on the fractal dimension was applied. The obtained results confirmed that the use of the fractal dimension enables the quantitative assessment of thrombogenicity and the proper qualification of samples in line with an expert's judgment. The polyurethanes showed the best thrombogenic properties of the tested samples: Bionate 55D (TR = 0.051) and PET-DLA 65% (average TR = 0.711). The ceramics showed the worst thrombogenic properties (TR = 1.846). All the tested materials were much less thrombogenic than the positive control (TR = 5.639).

Investigation on Ultrasonic Vibration Effects on the Plastic Flow Behavior of Ti2AlNb Alloy: Johnson–Cook Model

Investigation on Ultrasonic Vibration Effects on the Plastic Flow Behavior of Ti2AlNb Alloy: Johnson–Cook Model

Gradient microstructure response in different phases of Ti2AlNb alloy with laser shock peening

Ti2AlNb alloy is a new type of lightweight and heat-resistant structural material that has been an active research topic with multi-phases due to its improved mechanical properties. However, the phase response under severe plastic deformation (SPD) at high strain rates is unclear, which limits the understanding of its strengthening mechanism. Here, laser shock peening (LSP) was employed to investigate the microstructure response of α2, O, and B2/β phases in Ti2AlNb alloy. After LSP, the highest density dislocations were generated in the B2/β phases, followed by the O phases, and the least dislocations were observed in the α2 phases. In the B2/β phases, only dislocation tangles (DTs) were observed. Dislocation lines (DLs) and DTs were mainly distributed in the O phases. As for the α2 phases, DLs were generated while a small number of DTs were piled up at the grain boundaries. In addition, parallel dislocations (PDs) with a spacing of about 135 nm can be observed on the surface of the α2 phases, and the dislocations interspersed between PDs were composed of screw dislocations with long segments. In addition to dislocation structures, stacking faults (SFs) were observed in both α2 phases and O phases, and mechanical twins were formed in the O phases, which were generated to coordinate the SPD induced on the surface. These dislocation structures formed dislocation cells (DCs) and sub-grain boundaries which further developed into high-angle grain boundaries (HAGBs) together with mechanical twins, dividing the coarse grains and refining the microstructure. As the depth increased, the responses of the three kinds of phases decreased. The PDs in the α2 phases have widened spacing and could not penetrate the grains. The mechanical twins were gradually reduced until no obvious twin structure could be observed. Finally, dislocations, grain size, microhardness, and residual stress presented a gradient distribution. The improved microhardness (maximum 470 HV) and compressive residual stress (maximum −600 MPa) which were consistent with the refined grains and high-density dislocations gradually decreased to that of the base metal (BM).

Tensile behavior, microstructural evolution, and deformation mechanisms of a high Nb-TiAl alloy additively manufactured by electron beam melting

To evaluate the tensile behavior, microstructural evolution, and deformation mechanisms of Ti-45Al-8Nb alloy additively manufactured by electron beam melting, uniaxial tensile experiments were performed at a constant strain rate of 2.5 × 10−4 s−1 at various temperatures. The experimental results indicated that the tensile behavior and flow stress are sensitive to temperature. The brittle to ductile transition temperature of Ti-45Al-8Nb alloy additively manufactured by electron beam melting is between 700 and 750 ℃. Below this temperature, the fracture was predominantly trans-granular, resulting in brittle failure. In addition, the brittle failure behavior is related to the localization of deformation within the grains and stress concentrations owing to plastic incompatibility at the interface of the α2+γ phases. However, above this temperature, the fracture transformed from the trans-granular type to the mixed mode of trans-granular and ductile dimples. Dynamic recovery and recrystallization are the primary processes leading to softening behavior. The flow behavior at elevated temperatures results from the competition between work hardening and softening. Furthermore, the Chaboche model was used to describe the tensile inelastic behavior at different temperatures.

Research on high temperature deformation behavior and constitutive relation of Ti2AlNb alloy

A high-temperature plastic deformation is a failure form of Ti2AlNb alloy that deserves attention in the service process of aero-turbine engines. In this study, the deformation behavior of Ti2AlNb alloy has been studied through compression at 900 ~1100 °C and strain rates of 0.1 s−1, 0.01 s−1, and 0.001s−1. Then, the constitutive model of Ti2AlNb alloy has been established based on the true stress-strain curve. The results show that Ti2AlNb alloy has a high sensitivity to strain rate and temperature at the experimental condition. Ti2AlNb alloy still maintains good resistance to deformation at 900 °C, and the microstructure at the core region is basically unchanged after compression. In the boundary region, the microstructure changes significantly under the influence of stress. However, the yield strength of Ti2AlNb alloy decreases to about 5 MPa at 1100 °C, 0.001s−1, and the microstructure of the alloy has significant transformation which the O-phase structure decomposes and forms the α2 strip structure.

The preparation of gradient titanium alloy through laser deposition

Functionally gradient materials (FGMs) with continuous variation in composition or microstructure can realize gradient properties in different positions of the same component. The layer-by-layer laser deposition additive manufacturing is one of the most promising technologies that prepare FGMs with gradient properties. The present study is focused on the preparation of gradient titanium alloy by laser depositing Ti2AlNb powders on the substrate of a near-α high temperature titanium alloy. The microstructure, composition, and micro-hardness of prepared gradient titanium alloy with and without transition layer were compared and analyzed. Results show that an obvious bonding interface with variant microstructure morphology and element contents formed during directly deposited Ti2AlNb powders on near-α titanium alloy substrate and the bonding interface exhibits higher micro-hardness than the substrate and the deposited zone. However, the microstructure and the element exhibit gradient distribution characteristics along the deposition direction after adding the mixed powders of both two alloys as intermediate transition layers between the near-α titanium alloy and the Ti2AlNb alloy. The gradient distributed micro-hardness from the substrate to the top deposited zone sufficiently demonstrates the feasibility of obtaining gradient properties of gradient titanium alloy with composition transition layer during laser depositing.

Enhancement of tensile properties of Ti2AlNb alloy added with Ta element

• The Ta addition improved the tensile properties by solution strengthening. • The optimum heat treatment route was 970℃/1h/WQ+800℃/24h/AC. • After optimum heat treatment, the alloy has good tensile properties at 650℃. • The fracture mode is transgranular fracture with ductile dimples. Nb was replaced partially by Ta in Ti 2 AlNb alloy, resulting in elevated tensile strengths at high temperatures. The yield and tensile strength are up to 985 MPa and 1080 MPa at 650℃, respectively. Meanwhile, the elongation maintained a high level and the value reached 13%. The microstructure and deformation mechanism at high temperatures were investigated. The results revealed that the Ta addition improved the tensile properties by solution strengthening. Our findings provided new insights into designing the Ti 2 AlNb alloy with high strength and toughness.

Effect of cyclic DHT on microstructural evolution and mechanical properties of Ti44Al6Nb1Cr2V alloy

To clarify effects of microstructure on tensile properties of high Nb-TiAl alloys after cyclic directional heat treatment (DHT), Ti44Al6Nb1Cr2V alloys are conducted DHT for 1, 2 and 3 cycles (DHT-1, DHT-2 and DHT-3) at 1730 K, respectively. The pulling rate is set as 4.17 µm/s. Results show the phase component mainly consists of γ, α2 and B2 phases for Ti44Al6Nb1Cr2V alloy after cyclic DHT. Directional microstructure is obtained. Lamellar clusters are columnar and B2 phases present banded morphology. They are distributed alternately. As DHT cycles increase, the radial size of lamellar clusters enlarges as well. Blocky γ phases grow up and coarsen. At room temperature, good tensile properties are obtained in Ti44Al6Nb1Cr2V alloys after cyclic DHT. Tensile strength is about 609 MPa for DHT-1 alloy. Their fractures show that cleavage microstructure is mainly formed for cracks propagation during tensile test. Both DHT-1 and DHT-3 alloys present good tensile properties stability at 900 °C. Their yield strength, ultimate tensile strength and elongation are about 355–487 MPa-3.3% and 355–421 MPa-1.5%, respectively. Combining their microstructures with fractures, it concludes for their tensile properties difference that many blocky γ phases precipitate and coarsen during cyclic DHT, which decreases deformation coordination between lamellar clusters and banded B2 phases. Some microcracks form easily near B2 phases. Consequently, tensile properties of DHT-3 alloy decrease. This study will provide basic experimental data and theoretical support for high Nb-TiAl alloys to further optimize DHT parameters and improve their mechanical properties.

Biofunctional impact of textured coatings in the application of heart assist therapy

Due to a lack of organs, cardiac support systems are being implanted in patients with severe congestive heart failure. One of the solutions to overcome complications such as inflow obstruction or pump thrombosis, which may occur in the case of ventricular assist devices, is to modify the surface of cannulas for the controlled blood clotting process. The results obtained up till now for developed surface coatings clearly show the influence of topographical and mechanical parameters of the coatings on cell viability and protein adsorption mechanism. The new coatings should enable the controlled growth of scar tissue, resulting in the limitation of thromboembolic events, and the reduction of cystic tissue growth into the flow lumen. The aim of this study is to evaluate the correlation between surface topography parameters on the susceptibility of cells to grow and adhere to the substrate as a solution with potential for use in MCS (mechanical circulatory support) devices. Research on surfaces used in MCS devices and on inflow cannulas has been carried out for many years, while the novelty of the present solution makes it a milestone within that type of application simultaneously allowing for appropriate selection of process parameters. Surface modification of titanium alloy Ti6Al7Nb was carried out using vacuum powder sintering of CP-Ti (commercially pure titanium) powder with two morphologies (regular spheres and irregular grains). The characterization of coatings obtained with the proposed method and the influence of measured topographic parameters (applying scanning electron microscopy, contact angle measurement and contact profilometry) on the cytotoxicity and susceptibility to protein adsorption were presented. Advanced albumin adsorption studies have fully confirmed the dependence of surface complexity on protein adsorption. The obtained results show a high potential of the produced coatings toward enabling permanent integration at the implant with the soft tissue.

Research on Cracked Conditions in Nickel Chrome Alloy Ni50Cr33W4.5Mo2.8TiAlNb, Obtained by Direct Laser Deposition

Nowadays, additive manufacturing (AM) is a powerful way to make complex-shaped components for airspace engineering from nickel-based superalloys. So, while nickel-based superalloys could easily be we L-DED in sheet-metal thicknesses, they suffered from strain-age cracking and solidification during AM or in the post-weld aging treatment. This is attributed to the fact that besides the limitation of γ′- phase forming elements (Al and Ti), as they form by AM very rapidly and reduce ductility, the majority of the superalloys contain carbide-forming elements such as Cr, Mo, and W. The precipitation of carbides, which is very effective in strengthening, develops cracks in the heat-affected zone (HAZ) during AM. The difference in isochoric heat capacities and the thermal expansion coefficient (TEC) at the phase boundary leads to the appearance of dangerous local destruction energy. If the area of the interfacial interface is sufficiently extended, then the accumulation of this energy reaches a level sufficient for a crack formation. We have proposed a crack initiation criterion (CIC) for assessing the dangerous level of fracture energy. The CIC was derived from an estimate of the local energy balance from the heat transfer equation for the two-phase area. Practical approbation of the criterion was carried out after L-DED of samples from Ni50Cr33W4.5Mo2.8TiAlNb (EP648) alloy powder with an increased carbon content based on the study of the chemical composition near the crack formed during solidification. Using the proposed criterion provides an opportunity to give the rank to carbide-forming elements according to the degree of their influence on the fracture energy. Thus, the release of aluminum carbide turned out to be 5.48 times more dangerous than the release of titanium carbide and more than 5 times more dangerous than the release of tungsten carbide and molybdenum.

Microstructure and biocorrosion studies of spark plasma sintered yttria stabilized zirconia reinforced Ti6Al7Nb alloy in Hanks' solution

A study of spark plasma sintered Ti6Al7Nb alloy reinforced with yttria stabilized zirconia (YSZ) has been carried out to assess the biocorrosion response in Hank's solution. The results indicate that the microstructural changes resulting from YSZ addition to Ti6Al7Nb were considerably different from pure Ti6Al7Nb. All the Ti6Al7Nb + YSZ composites showed a higher Vickers microhardness value with Ti6Al7Nb + 10%YSZ exhibiting the most enhanced hardness value of 955.3 HV0.1. Furthermore, all Ti6Al7Nb + YSZ present higher corrosion resistance in Hank's solution than Ti6Al7Nb alloy except Ti6Al7Nb + 1YSZ which shows a significant drop in Ecorr and Icorr values. This could be due to grain refinement with less stable oxide film growth kinetics. The combination of mechanical property and corrosion resistance of the fabricated Ti6Al7Nb + YSZ alloy could make it a suitable material for dental implant in the nearest future.