Al Nb Research Articles

Investigation on double TiN/Al(Nb,Ta)2 protective layers of TiAl-Ta alloy after high-temperature oxidation

The formation process of the double continuous TiN/AlNb2 protective oxide layers of TiAl-Ta alloy after high-temperature oxidation is investigated by experiment and first-principle calculation in this study. It is found that Ta promotes the formation of a double continuous protective barrier consisting of 2.5 μm TiN/0.5–1 μm Al(Nb,Ta)2 layers during high temperature oxidation. And the lowest energy of twenty different AlNb2(1‾10)/TiN(110) terminations are identified by the first-principle calculation, which is significantly influenced by the distance of Nb-N bonding. Based on this, the location of Ta is studied which is preferred to be doped at Nb position of AlNb2 for the formation of Al(Nb,Ta)2 phase, thereby minimizing the total energy of the system. The formation of Al(Nb,Ta)2 phase can facilitate the precipitation of a continuous TiN layer to form a strong interface with low energy. Finally, the formation mechanism of Al(Nb,Ta)2(1‾10)/TiN(110) is discussed in detail. The results provide new insights into the development of oxidation-resistant TiAl alloys.

Structural-phase state and properties of heat and wear resistant cast irons of Cr–Mn–Ni–Ti system additionally alloyed with Al and Nb

The paper presents the data on phase composition and structure forming for the alloys, on distribution of elements among the alloy structural components, on variation of wear resistance, scale resistance, growing stability and mechanical properties of cast iron of Cr–Mn–Ni–Ti–Al–Nb system depending on different aluminium and niobium content and thermal ac-cumulating capacity of a casting mould. Complex carbides (Nb, Ti)C are forming in white cast iron during niobium alloying. Quantitative metallographic analysis of (Nb, Ti)C carbides and (Cr, Fe, Mn)7C3 complex carbides was carried out on the samples with examined composition. Aluminium provides favourable influence on forming of the thin protective spinel-type films with minimal amount of defects; diffusion through such oxide film is very difficult. Joint alloying by aluminium and niobium leads to simultaneous increase of heat resistance and wear resistance. Wear resistance increased as a result of enlargement of the part of primary carbides (Nb, Ti)C with high hardness in the structure of cast iron. Composition of oxide films includes aluminium, which strengthens their protective properties and rises of the alloy scale resistance. It is found for the first time that niobium doping leads to secondary solidification during cooling in the casting mold. Dispersion particles of М7С3 carbides are forming in solid state, thereby no structure degradation occurs during testing at increased temperatures, and growing stability rises. On the basis of the complex of the conducted researches the rational composition of heat and wear resistant cast iron is offered at the following ratio of components, wt. %: 2.1–2.2 C; 4.5–5.0 Mn; 18.0–19.0 Cr; 1.0–1.2 Ni; 0.4–0.6 Ti, 2.0 Nb; 2.0 Al. Wear resistance increased 1.2 times compared to cast irons before the introduction of aluminum and niobium, and scale resistance – 2.4–4.5 times depending on the type of casting mold, the index of growth resistance is equal to zero for cast irons cast in dry SLM

Microstructure and mechanical properties of non-heat-treated Al–8Si-0.2Mg-0.5Mn alloy inoculated by Al–Nb–B refiner

Al–Nb–B refiner has been considered as an alternative to Al–Ti–B refiner for hypoeutectic Al–Si alloys due to Si-poisoning effect. In this paper, the effects of Al–Nb–B and Al–Ti–B refiner on the microstructure and mechanical properties in indirect squeeze casting Al–8Si-0.2Mg-0.5Mn alloy were compared. Results show that the grain sizes in the edge chilling layer, segregation band, and the center region of the Al–Nb–B refined alloys were refined by 13.9%, 12.5%, and 17.6% compared to Al–Ti–B refined alloys, respectively. The yield strength, tensile strength, and elongation of Al–Nb–B inoculated alloys were superior to those of the unrefined alloys and Al–Ti–B inoculated alloys. The coexistence of NbAl3 and NbB2 particles in the Al–Nb–B refiner exhibited excellent anti Si-poisoning capability. They significantly decreased the grain size and uniformly distributed the eutectic Si particles and Fe-rich phases, resulting in an increase in the yield strength of the alloy by 16.1% compared to the Al–Ti–B inoculated alloy. The distribution of iron-rich phases in the segregation band was affected by the inoculation. The size of α-Al15(Fe, Mn)3Si2 phase in Al–Ti–B inoculated alloys was refined, and the number significantly increased, resulting in a decrease in tensile strength of 12.82 MPa. In the Al–Nb–B inoculated alloys, the size and number of α-Al15(Fe, Mn)3Si2 phase decreased, and the δ-Al4FeSi2 phase increased, which effectively improved the fracture toughness and ductility. In addition, with the increase in grain refinement (from unrefined to Al–Ti–B to Al–Nb–B inoculated alloy), the fracture behavior changed from trans-granular fracture to intergranular fracture, improving the fracture toughness.

Diffusion coefficients and atomic mobilities in the BCC phase of the Al–Nb–V system

Diffusion coefficients in the BCC phase of the Al–Nb–V ternary system are studied for the first time, including an assessment of the atomic mobilities. Ternary interdiffusion coefficients are obtained from the intersecting diffusion paths of several sets of diffusion couples that are annealed at both 1100 °C and 1200 °C. Existing experimental data from the pertinent binary systems are also employed for the assessments of atomic mobilities using the 1-parameter Z-Z-Z binary diffusion coefficient model developed by Zhong et al [1]. Interdiffusion coefficients in the BCC region of the Al–V system are also extracted through a forward-simulation analysis and incorporated into the mobility modeling. A complete description of diffusion in the BCC phase of the Al–Nb–V system is presented following the Binary and Cross-Binary Parameters Only (BCBPO) model developed by Zhong and Zhao [2]. Our data will be valuable input to diffusion-related simulation of refractory high entropy alloys containing aluminum.

The Effect of Refined Coherent Grain Boundaries on High-Temperature Oxidation Behavior of TiAl-Based Alloys through Cyclic Heat Treatment

The grain size of the full lamellae TiAl-based alloy changes from ~400 μm to ~40 μm through the precipitation of metastable structures by cyclic heat treatment. Based on this, two kinds of variant selection processes—coherent metastable γ variants precipitated during the air-cooling process and αs variants precipitated during the holding at a single α phase region process—are identified to promote the formation of refined Type I and Type II coherent grain boundaries. The oxidation tests at 1000 °C for 100 h show that the formation of refined coherent grain boundaries can greatly improve oxidation resistance by inducing the continuous multi-layer protective barrier consisting of (Ti, (Nb, Ta))O2, TiN, and Al(Nb,Ta)2. This protective barrier inhibits the inward diffusion of oxygen and nitrogen.

Strengthening behavior and model of ultra-high strength Ti–15Mo–2.7Nb–3Al–0.2Si titanium alloy

The microstructure evolution and strengthening behavior of the ultra-high strength Ti–15Mo–2.7Nb– 3Al–0.2Si titanium alloy were studied utilizing XRD, OM, SEM, and TEM analyses. The results show that the dislocation-strengthening and precipitation-strengthening effects could mostly affect the yield strength of this alloy. The highest yield strength of 1518 MPa was obtained under a combined process of cold rolling + recrystallization + cold rolling + duplex aging. This trend is mainly due to the high density of remaining dislocations, as well as dense and thin secondary α phases in microstructures. A theoretical composite-strengthening model was built, and the prediction error is within 16.6%. Furthermore, it is found that increasing the content of the secondary α phase can continuously strengthen the intragrain zone. This feature causes the intergranular fracture to appear and gradually dominate the fracture surface.

Electrochemical and Tribological Performance of Ti–Al with xNb Addition Synthesized via Laser In situ Alloying

Additive manufacturing is a growing technique of producing 3D parts directly using metal powders or wires melted with a high-powered intensity beam or laser. It is still a challenging process as to how laser processing parameters such as gas flow rate and powder flow rate can profitably be adopted to significantly produce Ti–Al-based materials from elemental powders to synthesize alloys that are defect-free and have good mechanical properties. The density of titanium aluminide (Ti–Al) intermetallic alloys makes it gain lots of interests due to its potential ability to substitute nickel-based superalloys in gas turbine engines. This work aims to investigate the effects of Niobium (Nb) additions on Ti–Al–xNb ternary alloys created via the use of 3D printing technology, specifically looking at microstructural evolution, microhardness, electrochemical behavior, and tribological properties. Ti–Al–Nb alloy was synthesized at scan speed of 26 in/min and laser power of 450 W. The structural morphology of the alloys produced was investigated using scanning electron microscopy equipped with energy dispersive spectroscopy and the electrochemical studies of the in situ alloyed Ti–Al–xNb were studied using potentiodynamic techniques. Using an Emco microhardness tester, the microhardness characteristics of the produced TiAl–xNb alloys were examined. From the results obtained, it was observed that the microstructure showed not much substantial cracking or crack initiation. The micrographs are evident of refined microstructure associated to increase in Nb feed rate with α-Ti3Al, γ-TiAl and precipitates of β-TiAl phases as the distinctively identified in the microstructure. The highest recorded microhardness value of 679.1 HV0.5 was achieved at Nb feed of 0.5 rpm and gas carrier of 2 L/min. The fabricated Ti–Al–Nb alloys showed good corrosion resistance behavior in HCl and appreciable wear characteristics with coefficient of friction of 0.412, 0.401, and 0.414 µ at B1, B3, and B5, respectively.

Al–Cr/Y–Al–O Layer Coating Oxidation on Ti–Al–Nb Intermetallic Alloy During Heating and Thermal Cycles

Al–Cr/Y–Al–O Layer Coating Oxidation on Ti–Al–Nb Intermetallic Alloy During Heating and Thermal Cycles

Compactability Regularities Observed during Cold Uniaxial Pressing of Layered Powder Green Samples Based on Ti-Al-Nb-Mo-B and Ti-B

We determined the compactability regularities observed during the cold uniaxial pressing of layered powder green samples, taking into account factors such as composition, height, and number of Ti–B (TiB) and Ti–Al–Nb–Mo–B (TNM) layers. The following composition was chosen for the TNM layer at %: 51.85Ti–43Al–4Nb–1Mo–0.15B, while for the Ti-B layer we selected the composition wt %: Ti-B-(20, 30, 40) Ti. Green samples were made containing both 100 vol % TiB and TNM, and those taken in the following proportions, vol %: 70TiB/30TNM, 50TiB/50TNM, 30TiB/70TNM; multilayer green samples were studied in the following proportions, vol %: 35TiB/30TNM/35TiB, 25TiB/25TNM/25TiB/25TNM, 35TNM/30TiB/35TNM. Based on the obtained rheological data, we determined the rheological characteristics of the layered green samples, including compressibility modulus, compressibility coefficient, relaxation time, and limiting value of linear section deformation. These characteristics were found to vary depending on the composition, height, and number of layers. Our findings revealed that reducing the TNM content in the charge billet composition improves the compaction of powder materials under the given technological parameters of uniaxial cold pressing. Moreover, we observed that increasing the boron content and decreasing the amount of titanium in the Ti–B composition enhances the compactability of powder materials. We also established a relationship between the compaction pressure interval and the density of the layered powder green sample.

Composite Material with a Ti–Al–Nb Matrix Reinforced with Sapphire Fibers

Composite Material with a Ti–Al–Nb Matrix Reinforced with Sapphire Fibers

Experimental investigation of phase equilibrium in the Al–Nb–Hf ternary system at 600 °C and 400 °C

The phase equilibria in the Al–Nb–Hf ternary system at 600 °C and 400 °C were experimentally investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and electron probe microanalysis (EPMA/WDS). In each isothermal sections, 13 three-phase regions were measured. And their phase region boundaries were precisely determined. Among the actually measured binary compounds, only Al3Nb, AlNb2 and AlNb3 have a large range of solid solubility. In addition, two stable ternary compounds τ1-Al11Nb4Hf5 and τ2-Al2NbHf2, which had certain solid solubility, were newly discovered. On the basis of the experimental results and reasonable inference, the isothermal sections of ternary system at 600 °C and 400 °C were constructed.

Cold uniaxial deformation of powder materials based on Ti‒B/Ti‒Al‒Nb‒Mo‒B

Cold uniaxial deformation of powder materials based on Ti‒B/Ti‒Al‒Nb‒Mo‒B

Microstructure and Mechanical Properties of a Precipitation‐Strengthened Fe–Al–Nb Alloy

Fe–Al alloys provide an attractive property profile for applications at temperatures of up to 700 °C. Herein, a Fe–25Al–2Nb (at%) alloy is, manufactured on an application‐relevant scale. Preforms are cast and subsequently forged into a turbine blade shape. The microstructural evolution and mechanical properties, namely quasistatic strength and creep response, are tested in different manufacturing conditions and are compared to the properties of equilibrated laboratory alloys, as well as to literature results. The cast process leads to coarse‐grained initial nonequilibrium microstructures with lower amounts of Laves phase as compared to thermodynamic equilibrium. Forging at 900 °C leads to the significant formation of subgrains in the Fe–Al matrix and precipitation of the Laves phase. The as‐cast condition of Fe–25Al–2Nb exhibits a complex creep behavior governed by the transient formation of a coherent Heusler phase as well as Laves phase formation and recrystallization in later stages of creep. In the forged condition, the material behaves similarly to long‐term annealed material. Although Fe–25Al–2Nb has slightly lower strength and lower creep resistance over the entire temperature range tested, it performs well compared to Ta‐containing Fe–Al alloys due to its lower cost and density.

Microstructure and properties of Al0.5NbTi3VxZr2 refractory high entropy alloys combined with high strength and ductility

Novel lightweight Al0.5NbTi3VxZr2 (x = 0.5, 1.0, 1.5) refractory high entropy alloys were synthesized by vacuum arc melting. The microstructure evolution and mechanical properties of Al0.5NbTi3VxZr2 alloys were analyzed. All Al0.5NbTi3VxZr2 alloys have a single BCC structure, and the addition of V does not change the microstructure of the alloys. At elevated temperatures, V1.0 alloy shows good phase stability, and the compressive yield strength of V1.0 alloy is 898 MPa at room temperature, 706 MPa at 873 K, and 110 MPa at 1073 K, respectively. Al0.5NbTi3VxZr2 alloys reveal excellent compression deformability, all samples can be compressed to more than 50% strain at room and elevated temperatures without fracture. At room temperature, V1.0 alloy still possesses the best tensile properties, with the yield strength of 694 MPa. The enhancement strength is due to the addition of V element with small atomic radius, which is caused by a variety of strengthening mechanisms, including solid solution strengthening and grain refinement strengthening. Most of the reported Al–Nb–Ti–V–Zr system refractory high entropy alloys have poor deformability at room temperature, and most of the work is focused on their compression properties. The Al0.5NbTi3VxZr2 refractory high entropy alloys prepared in the present work not only have excellent compression deformability, but also excellent tensile properties. Our present study not only promotes the development of toughening Al–Nb–Ti–V–Zr system refractory high entropy alloys to challenge engineering applications, but also provides guidance for the design of lightweight high temperature materials with a variety of strengthening mechanisms.

Композит с матрицей на основе Ti—Al—Nb, армированной волокнами сапфира

The structure of a layered composite material with a Ti—Al—Nb matrix reinforced with sapphire fibers has been studied. The composite was produced by diffusion welding under pressure of a multilayer package of alternating titanium and aluminum foils and unidirectional sapphire fibers, the gaps between which were filled with a suspension of niobium powder in polyethylene glycol. The strength of the prototype composite during the three-point bending test was 460 MPa at 20 °C and 140 MPa at 1100 °C. The deformation curves and developed fracture surfaces indicate the non-brittle nature of the fracture of the composite structure containing brittle components.

New approach to the compound energy formalism (NACEF) Part II. Thermodynamic modelling of the Al–Nb system supported by first-principles calculations

In the present work, a new assessment of the Al–Nb system, using a combined first-principle and CALPHAD approach, is presented. Formation enthalpies of all ordered configurations of the intermetallic phases (σ, D022 and A15) were estimated from ab initio calculations. The liquid, fcc and bcc phases are described by a substitutional solution model. The intermetallic phases D022 and A15 are described with the New Approach to the Compound Energy Formalism (NACEF). To model the σ phase, four descriptions are applied. In first, σ phase is described with the five-sublattice (5SL) model using combined CEF model where a modification was applied which allows to respect the formation enthalpies of end-members obtained from ab initio calculations. Then, a comparison with the results obtained using the NACEF approach applied to the five-sublattice (5SL), three-sublattice (3SL) and two-sublattice (2SL) models is presented. In all cases, assessments derived from the different descriptions of σ phase show very good agreement with the available experimental and ab initio data with a limited number of used parameters. In this sense, self-consistent thermodynamic descriptions of the Al–Nb system is provided. Moreover, this work shows from the example of the σ phase that the NACEF approach, contrary to what is commonly considered, allows the compatibility between different descriptions using different numbers of sublattices. This is particularly interesting for the construction of multi-component databases.

The Reaction Products of the Al-Nb-B2O3-CuO System in an Al 6063 Alloy Melt and Their Influence on the Alloy's Structure and Characteristics.

To meet aero-engine aluminum skirt requirements, an experiment was carried out using Al-Nb-B2O3-CuO as the reaction system and a 6063 aluminum alloy melt as the reaction medium for a contact reaction, and 6063 aluminum matrix composites containing in situ particles were prepared with the near-liquid-phase line-casting method after the reaction was completed. The effects of the reactant molar ratio and the preheating temperature on the in situ reaction process and products were explored in order to determine the influence of in situ-reaction-product features on the organization and the qualities of the composites. Thermodynamic calculations, DSC analysis, and experiments revealed that the reaction could continue when the molar ratio of the reactants of Al-Nb-B2O3-CuO was 6:1:1:1.5. A kinetic study revealed that the Al thermal reaction in the system produced Al2O3 and [B], and the [B] atoms interacted with Nb to generate NbB2. With increasing temperature, the interaction between the Nb and the AlB2 produced hexagonal NbB2 particles with an average longitudinal size of 1 μm and subspherical Al2O3 particles with an average longitudinal size of 0.2 μm. The microstructure of the composites was reasonably fine, with an estimated equiaxed crystal size of around 22 μm, a tensile strength of 170 MPa, a yield strength of 135 MPa, an elongation of 13.4%, and a fracture energy of 17.05 × 105 KJ/m3, with a content of 2.3 wt% complex-phase particles. When compared to the matrix alloy without addition, the NbB2 and Al2O3 particles produced by the in situ reaction had a significant refinement effect on the microstructure of the alloy, and the plasticity of the composite in the as-cast state was improved while maintaining higher strength and better overall mechanical properties, allowing for industrial mass production.

High specific yield strength TiZrAlNbV high-entropy alloys via coherent nanoprecipitation strengthening

Developing lightweight high-entropy alloys (LHEAs) having considerable strength and ductility is a new perspective in the quest of novel lightweight alloys for potential engineering applications. The paper describes that by tailoring the aging treatment, abundant coherent B2 nanoprecipitates can be induced in body-centered-cubic (BCC) Ti–Zr–Al–Nb–V LHEAs. These nanoprecipitates can strengthen the alloys by around 20% based on the dislocation-shearing mechanism. Moreover, due to the effective inhibition of these precipitates on dislocation propagation, frequent cross-slip events appear, which benefit the deformation delocalization. Finally, based on the B2 precipitation strengthening, a LHEA having specific yield strength as high as ∼202 MPa m3/kg and considerable fracture strain of ∼25% is developed. Our results provide a solution to overcome strength-ductility trade-off for the alloy to be suitable for structural applications.

Influences of Al concentration and Nb addition on oxidation behavior of Ti2AlC ceramics at high temperatures

ABSTRACT A titanium aluminum carbide, Ti2AlC, which is classified among MAX phase ceramics, was studied as a potential candidate for various mechanical components used in high-temperature applications. The impact of its chemical composition on its high-temperature oxidation process was determined. Ti2AlC powders with various Al contents and with or without Nb addition were synthesized via a conventional reaction technique followed by 16 h of annealing in vacuum at 1300°C. The synthesized Ti2AlC powders were consolidated by means of 15 min of pulsed electric current sintering at a die temperature of 1300°C in vacuum under a uniaxial pressure of 30 MPa. In the presence of an aluminum reservoir in the form of TiAl3, Ti2AlC has excellent resistance against high-temperature oxidation. The promising results concerning the addition of Nb to TiAl provided the rationale for a similar modification of Ti2AlC. The results of oxidation tests on Nb-doped Ti2AlC likewise showed excellent oxidation resistance. Alloying with Nb can improve the oxidation resistance of Ti2AlC with low Al content, allowing the formation of a protective Al2O3 scale and inhibiting the growth of TiO2.

Elimination of room-temperature brittleness of Fe–Ni–Co–Al–Nb–V alloys by modulating the distribution of Nb through the addition of V

Compared with Ti–Ni-based and Cu–Al-based alloys, Fe–Ni–Co–Al-based superelastic alloys have received great attention in recent years because of their low cost and excellent performance. However, the precipitation of brittle precipitates on grain boundaries in Fe–Ni–Co–Al-based polycrystalline alloys significantly reduces the mechanical properties. In this paper, the effects of V on the formation of brittle precipitates on both grain boundaries and inside grains and mechanical properties in Fe–Ni–Co–Al–Nb alloy were investigated systematically. The results show that γ′(Ni3Al) precipitate with L12 structure precipitate out on grain boundaries and inside grains in the Fe–Ni–Co–Al–Nb alloy during aging without V addition. The γ′ precipitate with L12 structure on the grain boundaries grew to form a heavily-coarsened L12 precipitate (HCLP γ′ precipitate) due to the accumulation of Nb on the grain boundaries, resulting in a significant decrease in elongation. With the addition of V, intragranular Nb and V can combine together with γ′ to form Ni3(Al, Nb, V) (nano-sized γ′ precipitate) composite precipitates, which improves the strength. More important, since the diffusion coefficient of V was larger than that of Nb, V preferentially occupied the lattice positions on grain boundaries, repelling Nb from the grain boundaries to the matrix. Thus, the coarsening of HCLP γ′ precipitate on the grain boundaries was reduced, and the elongation of Fe–Ni–Co–Al–Nb–V alloy was significantly improved.