Ti2AlNb Alloy Research Articles

Microstructures and tensile properties of Ti2AlNb and Mo-modified Ti2AlNb alloys fabricated by hot isostatic pressing

The Ti2AlNb and Mo-modified Ti2AlNb alloys were fabricated by hot isostatic pressing, and then underwent annealing treatment at 800 °C for 1, 2 and 3 h respectively. To evaluate the tensile properties of the two kinds of alloys, tensile tests were conducted at ambient temperature and 650 °C in this study. For the Ti2AlNb alloy, the room-temperature ultimate tensile strength (UTS) was 700–900 MPa, and the highest elongation to failure (εf) reached 6.2% after aging for 2 h at 800 °C. Since the Mo addition promoted the precipitation of the coarse B2+O colony structure near the grain boundary, the Mo-modified Ti2AlNb alloy exhibited decreased UTS and εf at room temperature. As for the high-temperature performance of both the Ti2AlNb and Mo-modified Ti2AlNb alloys, the UTS reached approximately 700 MPa and the εf exceeded 3.0%. Meanwhile, the two kinds of alloys presented the same tendency that both the high-temperature UTS and εf increased firstly and then decreased as the aging time increased. Among them the specimens after aging at 800 °C for 2 h for both alloys acquired the highest UTS and εf. Moreover, the Mo-modified alloy exhibited a better high-temperature ductility than that at room temperature, which is associated with the B2↔O phase transformation during the loading at 650 °C. The Mo addition effectively refined the lath of the precipitates in the grain and the grain size of the matrix, and it induced abundant dislocations. Thus, the Mo-modified Ti2AlNb alloy aged for 1 and 3 h exhibited superior high-temperature mechanical properties than those of the Ti2AlNb alloy.

Comparison of Mechanical and Barrier Properties of Al2O3/TiO2/ZrO2 Layers in Oxide-Hydroxyapatite Sandwich Composite Coatings Deposited by Sol-Gel Method on Ti6Al7Nb Alloy.

In this study, coatings of different oxides (TiO2, Al2O3, ZrO2) and hydroxyapatite (HAp) as well as sandwich composite hydroxyapatite with an oxides sublayer (oxide+HAp) were deposited on Ti6Al7Nb alloy using the sol–gel dip-coating method. The coatings were characterized in terms of morphology (optical microscope), surface topography (AFM), thickness (ellipsometry), and crystal structure (XRD/GIXRD). The mechanical properties of the coatings—hardness, Young’s modulus, and adhesion to the substrate—were examined using nanoindentation and scratch tests. The barrier properties of the coatings against the migration of aluminum ions were examined by measuring their concentration after soaking in Hank’s balanced salt solution (HBSS) with the use of optical emission spectrometry of inductively coupled plasma (ICPOES). It was found that all the oxide and HAp coatings reduced the permeation of Al ions from the Ti6Al7Nb alloy substrate. The best features revealed an Al2O3 layer that had excellent barrier properties and the best adhesion to the substrate. Al2O3 as a sublayer significantly improved the properties of the sandwich composite HAp coating.

Development of antibacterial, ciprofloxacin-eluting biodegradable coatings on Ti6Al7Nb implants to prevent peri-implant infections.

Various types of biodegradable polymers containing lactide, glycolide, caprolactone, and trimethylene carbonate units have been used to obtain ciprofloxacin (CFX)-enriched coatings developed on the Ti6Al7Nb alloy, intended for short-term therapy. In the first step, the surface of the Ti6Al7Nb alloy was modified, mostly according to sandblasting and anodic oxidation to obtain the TiO2 layer. Anodizing can be an effective method for preparing TiO2 coatings with osteoconductive properties. The polymer containing CFX molecules was deposited on the modified alloy, and Polymer + CFX/TiO 2 /Ti6Al7Nb systems were developed. CFX-enriched coatings adhered well to the surface of the previously modified alloy. Polymer layers maintain the topography of the alloy due to the development of the surface during the sandblasting method. As polymers intended for the study possess degradation ability, they are capable of releasing the incorporated drug. Antibacterial activity of CFX-enriched coatings was examined to verify the functionality of designed Polymer + CFX/TiO 2 /Ti6Al7Nb systems, and the bactericidal effect was confirmed for all cases. The presented study is an extension of previous, initial research and creates an overview of polyester or polyestercarbonate CFX-eluting coatings.

Experimental investigation of bioceramic (Hydroxyapatite and Yttrium stabilized zirconia) composite on Ti6Al7Nb alloy for medical implants

ABSTRACTIn this experimental work, a mixture of Hydroxyapatite (HAp)+yttrium stabilized zirconia (YSZ) is deposited on a layer of Ti6Al7Nb alloy by electron-beam deposition method, which finds its application in bone and dental implants. Multi-criteria decision making method is adopted (TOPSIS) highlights the close to an ideal solution at the temperature of 160°C (Chamber), 950°C (Furnace), 30 mA (Energy), 90 min (Duration) for achieving the coated layer with optimal thickness. XRD revealed the heat treatment of the samples varying at 450°C and below, tend to shift the sample toward amorphous region due to the inherent nature of electron-beam deposition. To compensate for this, a post-heat treatment has been carried out. From SEM analysis, it is ascertained that coated specimen indicates minimal micro voids and pores, as seen in the cross-sectional area of the HAp/YSZ coated Ti6Al7Nb. The percentage increase from the stoichiometric YSZ and HAp (1.68) to 18.96% (1.99) and 19.20% (1.54) indicates the rise in elemental composition with rise in temperature, attributed to the dissolving nature of P, along with the boundaries of Zr and Ca. In the presence of HAp-YSZ, nano-coated specimen on the substrate would lead to a higher penetration depth along with increase in the strength of the bond formed (adhesive) in the specimen. In the presence of HAp/YSZ powder the corrosion rate falls by 49.34%, attributed to the presence of Zr in YSZ sample creating an addendum for osseointegration.

Effect of Mo, V and Zr on the microstructure and mechanical properties of Ti2AlNb alloys

Small button ingots of Ti2AlNb alloys with different contents of Mo, V and Zr were melted by vacuum non-consumable arc furnace. Due to the rapid cooling rate during melting process, only β grains without precipitation were observed in most of the button ingots and no regular phenomenon was found. However, when the samples were heated to β phase region and then furnace cooled to room temperate, different morphologies and quantities of primary α phase and second O phase formed from the β grains of different samples. It is suggested that the morphology of α phase was changed from lamellar to quadrilateral with increasing V and the lath O increased with increasing Zr. Besides, the residual β/B2 phase increased with increasing Mo and V. The EDS results showed that Al and Zr were enriched in α phase whereas Nb, Mo and V were enriched in β/B2 phase. The micro-hardness of these samples before and after heat treatment was detected and the micro-hardness increased with increasing Zr and decreasing Mo and V.

Deformation Behavior and Dynamic Recrystallization of Ti–22Al–25Nb Alloy at 750–990 °C

Ti–22Al–25Nb is a representative of Ti2AlNb alloys with excellent comprehensive properties, which has great application prospects in the aerospace field. Herein, high‐temperature tensile plastic deformation behavior and dynamic recrystallization process of Ti–22Al–25Nb alloy are researched during 750–990 °C. From 750 to 870 °C, plasticity is gradually improved with temperature increasing, and the fracture mode is crack aggregation. From 900 to 930 °C, the content of B2 phase increases and plasticity is significantly improved because crack along the grain is suppressed by combined precipitation of three phases B2 + O + α2 at grain boundaries with large areas. From 960 to 990 °C, the alloy is mainly composed of B2 phase and has best plastic deformation performance. Fully dynamic recrystallization of B2 phase happens at 990 °C. Texture strength is strengthened by intense plastic deformation, but it is weakened by dynamic recrystallization subsequently.

TEM investigations of active screen plasma nitrided Ti6Al4V and Ti6Al7Nb alloys

Direct current plasma nitriding (DC PN) helped to lower processing temperature as compared gas nitriding (GN) allowing to protect the surface with a layer of TiN compound and preserve the mechanical properties of the core material, which otherwise might lose its fine grain microstructure. However, samples of more complicated shapes are subjected to edge effects resulting in their overheating and uneven coverage. Introduction of active screen plasma nitriding (AS PN) should take care of both of these disadvantages, but the understanding on its effect on the compound and diffusive layers of processed parts is far from being clear. The present experiment was aimed at comparing the microstructure and the phase composition of DC PN and AS PN treated Ti6Al4V and Ti6Al7Nb alloys at temperatures of 680 °C and 740 °C. The microstructure investigations were performed with TEM/EDS methods, while phase analysis relied on electron diffraction indexing. It showed that switching from DC PN to AS PN resulted in covering it with a compact TiN layer backed with α″-Ti(N) martensite and Ti3Al-type layers, i.e. same as in the former case (DC PN) except the missing δ′-Ti2N layer. Additionally, it changes nitriding mechanism from absorption-diffusion of nitrogen ions to adsorption-diffusion of these species, what is a reason of slowing down of the rate of nucleation and growth of both the compound and diffusive layers. The growth of β-Ti(N) layer, which changes on cooling to α″-Ti(N) is controlled by in-diffusion of nitrogen to its front.

Surface Properties of Retrieved Cementless Femoral Hip Endoprostheses Produced from a Ti6Al7Nb Alloy

We have investigated new and retrieved cementless hip endoprostheses that prematurely failed due to (i) aseptic loosening, (ii) infection and (iii) latent infection. The aim was to better understand the physico-chemical phenomena on the surfaces and sub-surfaces of the Ti6Al7Nb alloy implant. The results of our studies should enable us to distinguish the causes of premature failure, optimize the surface modification, achieve optimal osseointegration and extend the useful lifetime of the implants. The surface properties of the Ti6Al7Nb alloys of the hip-stem endoprostheses (30 retrieved and 2 new) were determined by contact-angle measurements and the average surface roughness. The surface chemistry and microstructure were analysed by scanning electron microscopy (SEM) for morphology, energy-dispersive X-ray spectroscopy (EDS) for the chemistry, and electron back-scatter diffraction (EBSD) for the phase analysis; Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) for the surface chemistry; and electrochemical measurements for the corrosion. The improved wettability of the grit-blasted surface of the Ti6Al7Nb stems after autoclaving was measured, as was the super wettability after oxygen-plasma sterilization. The secondary-electron images showed that the morphology and microstructure of the new and retrieved stems (prematurely failed due to aseptic loosening, infection and latent infection) differ slightly, while the EDS analysis revealed corundum contamination of the grit-blasted surface. We found corundum-contaminated Ti6Al7Nb stem surfaces and sub-surfaces for all the investigated new and retrieved implants. These residues are a potential problem, i.e., third-body wear particles, and probably induce the osteolysis and aseptic loosening.

A Comparative Study on Microstructure and Mechanical Properties of Ti‐43/46Al–5Nb–0.1B Alloys Modified by Mo

To improve mechanical properties of TiAl–Nb alloys and obtain effects of Al content on microstructure, Ti‐43/46Al–5Nb–0.1B–xMo alloys are prepared. Phase constitution, macro‐/microstructure volution, and mechanical properties of them are investigated systematically and compared in detail. Results show that the lamellar colony size refines, B2 phase increases and Al‐segregation in interdendritic regions aggravates with the increase in Mo content. The increased B2 phase is attributed to the increased Mo segregated at the grain boundaries during β/α transformation, and the aggravated Al‐segregation is attributed to the increased Al rejected into the interdendritic areas during L/β solidification. Compressive results show that the strength and strain increase about 150 MPa and 6% when the Mo content increases to 0.8 at% for Ti‐43Al–5Nb–0.1B–xMo alloys; they increase about 343 MPa and 4% when Mo content increases to 1.2 at% for Ti‐46Al–5Nb–0.1B–xMo alloys. Both the strength and strain decrease when Mo content further increases. The grain refinement strengthening and solid solution strengthening caused by Mo are contributed to the improved strength and strain. However, excessive B2 phase and severe Al‐segregation deteriorate the mechanical properties of the alloys, which act as the cracking sources.

Effect of laser shock peening on microstructure and residual stress of Ti<sub>2</sub>AlNb alloy

Ti2AlNb-based alloys are developed from conventional titanium aluminides (TiAl-based alloys and Ti3Al-based alloys). Comparing with TiAl and Ti3Al-based alloys, Ti2AlNb-based alloys have better mechanical properties of strength density ratio, high temperature fracture toughness and creep resistance. It is expected to replace traditional high temperature materials such as nickel-based alloys for the manufacture of aero-engine components. Laser shock peening (LSP) is an advanced surface modification technology which induces high amplitude, large depth residual compressive stress on the surface of materials. It can effectively enhance mechanical properties of material such as micro-hardness, fatigue resistance, high temperature oxidation performance. Compared to other surface modification technologies such as shot peening and rolling, LSP can not only induce deeper compress residual stress (1–2 mm), which is about five to ten times deeper than that of shot peening, but it can refine the grain or even form nanocrystals which plays a significant role in enhancing properties of material. For these reasons, this surface treatment technology has been widely used in the aircraft and nuclear energy industries. In this paper, the surface modification of Ti2AlNb alloy was carried out by laser shock peening, and the microstructure evolution, residual stress and the performance at high temperature were investigated. The results show that laser shock peening can significantly reduce the grain size of the surface of Ti2AlNb alloy. Dislocation lines, dislocation tangles and dislocation walls were generated after LSP. The micro-hardness is increased from 350 HV to 395 HV and the effect layer is about 1.2 mm. The residual compressive stress of −337 MPa is generated on the surface of the sample. In addition, residual stress is released obviously at high temperature. The residual stress on the surface of sample reduces to −65 MPa after heat treatment at 720°C for 4 h. The residual stress is almost completely released after heat treatment at 720°C for 10 h. However, the release rate of residual stress is slowed down at 600°C. The effect of laser shock peening is still presence after heat treatment for 100 h.

Experimental equilibria of several β/βo–Ti–Al–Nb alloys containing ωo phase

The phase equilibria of several (6, 8, 10) at% Nb–TiAl alloys are experimentally determined by the morphologic, crystallographic and thermal analysis methods. The thermodynamically determined phase equilibria reveal that ωo phase transforms from α2 phase, having no β/βo phase retained at ambient temperature. While, the β/βo phase are experimentally observed in the samples annealed at 1400 °C followed by a slow cooling rate (∼10 °C min−1). Furthermore, the transformation of βo ↔ ωo, as well as the disorder-order transition of β ↔ βo, is unambiguously detected, within the certain transformation temperatures.

Electrically assisted superplastic forming/diffusion bonding of the Ti2AlNb alloy sheet

Electrically assisted superplastic forming and diffusion bonding (EASPF/DB) is based on the electrically assisted technique in which the electric current is directly and simply introduced into metallic sheets during hot processing. Through the rapidly increasing heat by the Joule effect after several minutes, the advantages of the EASPF/DB process are further strengthened, and the limitations of commercial exploitation (e.g., long processing period) are partly overcome. In this study, an experimental setup of EASPF/DB was assembled for the experimental validation of this concept. The Ti2AlNb alloy sheet, which is regarded as a superior substitute for the nickel-based alloy, was diffusion-bonded and formed, and a double-layer structure was fabricated by means of the EASPF/DB process. The temperature distribution measured by an infrared imaging camera was apparently influenced by detour effects of the electric current. To examine the forming and bonding effects, the height and thickness were measured in different positions. The microstructures of the bonding interface were observed, and no microcavity and crack were found, which indicated the feasibility of the variant of the SPF/DB process. Meanwhile, the large-size grains of B2 phase compose the microstructure of forming zone with some fine needle–like precipitates. Finally, the hardness test showed higher values of Vickers hardness than that of the as-received sheet and the compression test showed three stages of the double-layer structure during continuous loading. The important values and significance for use of this variant are presented by markedly reducing the heating and cooling time and the targeted heating manner for metallic sheets.

Microstructure and mechanical property of SiC whisker coating modified C/C composite/Ti2AlNb alloy dissimilar joints prepared by transient liquid phase diffusion bonding

SiC whisker coating was prepared on the surface of C/C composite successfully by CVD, and transient liquid phase (TLP) diffusion bonding was employed to realize the joining of SiC whisker coating modified C/C composite and Ti2AlNb alloy using Ti–Ni–Nb foils as interlayer. The microstructure, shear strength and fracture behavior were investigated by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD) and universal testing machine. The results show that SiC has good compatibility with C/C composite, and gradient interface formed between SiC-modified C/C composite and Ti2AlNb alloy. When the bonding experiment was carried out under bonding temperature of 1040 °C and holding time of 30min with 5 MPa pressure in vacuum, the joints formed well and no obvious defects can be observed. The typical microstructure of joints is C/C composite/SiC + TiC/Ti–Ni compounds + Ti–Ni–Nb solid solutions/residual Nb/diffusion reaction layer/Ti2AlNb alloy. With the increasing of bonding temperature, the thickness of joining area increased due to sufficient element diffusion. However, when bonding temperature is elevated to 1060 °C, some defects such as cracks and slag inclusions exist in the interface layer between interlayer and Ti2AlNb. The joints with maximum average shear strength of 32.06 MPa are bonded at 1040 °C for 30min. C, SiC and TiC can be found on the fracture surface of joints bonded at 1040 °C which indicated that fracture occurred at the interface layer adjacent SiC layer.

First-principles investigation on stability and oxygen adsorption behavior of a O/B2 interface in Ti2AlNb alloys

This work studied the stability and oxygen adsorption properties of interface between the O and B2 phases in Ti2AlNb alloys by first principles calculations. In term of their crystal structures, the connection between O(11‾0) and B2(211‾) slabs owns the minimum lattice mismatch, which was therefore built up as the O/B2 interface. Through a serious examination including the influences of terminal elements and relative positions on the stability of the interface, a HCP stacking, that the interfacial atoms of O phase are located at the top of the atoms in the second layer of B2 phase, was clarified as the most coherent interface between O(11‾0) and B2(211‾) slabs. Adsorption of oxygen atom in the interface was studied and the estimated adsorption energies show that this process is thermodynamically stable, but less stable than that on the O(010) surface, illustrating that the O/B2 coherent interface without defects has limited influence on the oxidation of Ti2AlNb alloys.

Fabrication of nano-TiC reinforced high Nb-TiAl nanocomposites by electron beam melting

Electron beam melting (EBM) has been successfully applied to fabricate TiC reinforced high Nb-containing TiAl matrix (TiC/Nb-TiAl) nanocomposite. The optimised combination of focus offset and line energy in the melt stage have been developed to achieve a uniformly distributed nano-TiC particles within the TiAl matrix. The EBM TiC/Nb-TiAl nanocomposite has a microhardness of 393 ± 31 HV0.2, that is 24% higher than that for high Nb-TiAl alloy alone. It is interesting to note that the uniformly distributed nano-TiC particles lead to the formation of equiaxed α2-phase in TiAl matrix, instead of those commonly observed γ-phase in previous EBM γ-TiAl work.

First-principles investigation on the atomic structure, stability and electronic property of O(001)/B2(110) interface in Ti2AlNb alloys

In the present work, first-principles calculation is employed to investigate the adhesion, stability and electronic property of Ti2AlNb O(001)/B2(110) interface. It is found that the Ti2AlNb O(001) surface slab and B2(110) surface slab can reach bulk-like characteristics when the atomic layers are larger than seven. Four kinds of Ti2AlNb O(001)/B2(110) interfacial models are investigated in consideration of different interfacial atom stacking sites. The adhesive work, interfacial energy and electronic structure of these four interface models are calculated. The results show that the Ti2AlNb O(001)/B2(110) interface with the bridge-stacking site 1, i.e. the interfacial atoms of O phase are located either between Al and Nb atoms or between two Ti atoms on the first atomic layer of B2(110) surface slab, shows the smallest interface distance (2.34 Å), the largest adhesion work (3.38 J/m2) and the lowest interface energy (0.41 J/m2), which indicates that this interfacial configuration is the most thermodynamically stable and is preferred equilibrium structure for the Ti2AlNb O(001)/B2(110) interface. The calculated electronic properties reveal that the maximum thermodynamic stability of Ti2AlNb O(001)/B2(110) interface with the bridge-stacking site 1 is mainly contributed from Ti–Nb covalent and Ti–Al covalent interactions.

Synthesis, structure, and properties of the high Nb–TiAl alloy after Ni coatings by plasma surface alloying technique

Ni coatings were prepared on the high Nb–TiAl alloy by the plasma surface alloying technique. The results found that surface morphology and microstructure exhibited a strong dependence on the deposited temperature. The elements diffusion during the metalizing stage leaded to the high hardness value and adhesion force between the Ni coating and substrate. The corrosion resistance of the Ni-coated specimens depended on the fabrication temperature related to the deposition and diffusion layers. For the oxidation, the weight gain rate was involved in the chemical reaction in the initial oxidation stage. The inter-diffusion among elements such as the nickel, titanium, and aluminum resulted in the high adhesion force after the oxidation, improving the bonding force between the Ni coating and substrate.

Features of In Vitro Interaction of Osteoblast-Like MG-63 Cells with the Surface of Ti-Zr-Nb Shape Memory Alloys

The effect of the surface of Ti-Zr-Nb (TZN) shape memory alloys (SMA) on adhesion, proliferation, viability, and organization of the actin cytoskeleton of osteoblast-like MG-63 cells has been studied. The studied SMA have a unique combination of mechanical properties, making them promising in fabrication of bone implants with high biomechanical compatibility (due to low Young’s modulus and superelastic behavior similar to that of bone tissue). Thin sheets of the experimental TZN alloy and Ti-Al-Nb (TAN) medical alloy (as a control) are used in the study. Growth dynamics of MG-63 cell culture is assessed by the MTT assay and counting the number of nuclei per unit area. It is found that the number of cells cultured on TZN alloy is higher than on TAN alloy on the fourth and seventh days. This may be due to the influence of the qualitative and quantitative composition of the materials on the microstructure and chemistry of the surface. The cell viability during the cell culturing on both alloys is close to 100%. Image-based actin cytoskeleton analysis has shown the predominance of fibrillar actin on the TZN samples and has also revealed the cytoskeletal organization or structure typical of polygonal-shaped fibroblast-like cells.

Influence of the Surface Roughness of Ti6Al7Nb Alloy on Its Behavior in Biotribological Systems

The paper presents the results of studies of Ti6Al7Nb alloy properties used in biotribological systems. The following physicochemical treatments of the alloy were compared: polishing, sandblasting, etching as well as sandblasting and etching. Element identification was performed using a scanning electron microscope equipped with an EDS microanalyser. Scanning and confocal microscopy was used to observe surface morphology and topography. Frictional tests were carried out using a ball-disk coupling in reciprocating motion in technically dry friction and friction with lubrication with Ringer’s solution. An optical tensiometer was used to determine the contact angle. As a result of the applied physicochemical treatments, surfaces of different morphology and geometric surface structure were obtained. The polished and etched sample had the most homogeneous surface. It was found that surface roughness significantly influences tribological properties. For the samples characterized by micro roughness of the surface, the best characteristics were obtained under conditions of technically dry friction. However, under the conditions of lubrication with Ringer's solution, the properties were the best for the samples characterized by nanoroughness. Ringer's solution reduced resistance to motion by approximately 20%. A negative influence of surface development on wetting was also found.

Study on Microstructure Evolution and Mechanical Properties of Ti2AlNb-Based Alloy under Canning Compression and Annealing

The influence of height reduction on the microstructure evolution and mechanical properties of the Ti2AlNb-based alloy was investigated during canning compression and subsequent annealing. After the annealing treatment, the spheroidized B2 phase grains occurred because of partial recrystallization. Meanwhile, the texture evolution of the B2 phase and O phase were analyzed under the deformation degree, ranging from 25% to 75%. The results show that the mechanical properties of the post-annealed alloys were co-affected by the grain size and Schmid factor of the B2 phase. When the height reduction was less than 25%, the compression strength was mainly affected by the grain size. When the height reduction was higher than 50%, it was mainly dominated by the Schmid factor. When the deformation degree reached 75%, the recrystallized grain size decreased to 0.9 μm. Meanwhile, the Schmid factor of a {110}<001> slip system in B2 phase reduced to 0.34. Therefore, the yield strength of the Ti2AlNb alloy at room temperature increased from 892 MPa in the as-rolled condition to 935 MPa after the canning compression and annealing.