Ti Al Zr Alloy Research Articles

Ternary Diffusion and Thermodynamic Interaction in the β Solid Solutions of Ti–Al–Zr Alloys at 1473 K

Interdiffusion in Ti-rich β solid solutions in Ti–Al–Zr alloys was investigated at 1473 K. In the β Ti–Al–Zr alloys, the main interdiffusion coefficients (i.e., and , respectively) and the cross interdiffusion coefficients, (i.e., and , respectively) have positive values, as well as a slight concentration dependence. The values of are larger than those of . In Ti–Al–X (= V, Cr, Fe, Co, Zr) alloys, the values of the main coefficients are at 1473 K. Repulsive interactions occur between Al and X (= V, Cr, Fe, Co, Zr) atoms in the Ti–Al–X alloys, because the ratio values of the cross coefficients to the main ones are positive in sign. On the other hand, the interactions between Ti (solvent) and X (= V, Cr, Fe, Co, Zr) (or Al) atoms are attractive in the present alloys because the ratio of the converted interdiffusion coefficients is negative values.

Investigations of cathodic reactions using cyclic voltammetry and electrochemical behavior of Ti–Al–Zr alloy in nitric acid using electrochemical impedance spectroscopy

Investigations of cathodic reactions using cyclic voltammetry and electrochemical behavior of Ti–Al–Zr alloy in nitric acid using electrochemical impedance spectroscopy

Oxidation resistance of SiO2 bonded coating formed on Ti–Al–Zr alloy

Methyl hydrogen silicone converted SiO2 bonded composite coatings with high infrared emissivity additives of Cr2O3 and Al2O3 were prepared on Ti–6Al–2Zr–1Mo–1V titanium alloy by a dipping and then pyrolysing process. The phase composition and microstructure of the coating were characterised by X-ray diffraction and scanning electron microscopy. The results show that after exposing the samples to an oxidative atmosphere at 600°C for 100 h, the coated samples pyrolysed at 600 and 800°C exhibit a significantly lower weight gain (0·11 mg cm−2) compared with that of the titanium substrate (0·54 mg cm−2). The weight gain for both coated samples oxidised at 800°C increases up to 1·4 mg cm−2, while the titanium substrate damages by oxide scale peeling. The coating pyrolysed at 800°C has a high infrared emissivity value of above 0·85, which is slightly higher than that of the coating pyrolysed at 600°C.

Corrosion behavior of anodized TiAlZr alloy in a hybrid electrolyte at different voltages

Corrosion behavior of anodic oxide layers on the surface of TiAlZr alloys formed using glycerol + 15 vol% H2O + 0.2 M NH4F under variable anodizing voltage (15 V, 30 V) was investigated and compared with corrosion of the native films. Electrochemical behavior analysis of all samples was composed of linear polarization, potentiodynamic polarization and electrochemical impedance and was correlated with the morphology data obtained from scanning electron microscopy and atomic force microscopy. Nanotubular structures appeared on the surface of the TiAlZr sample anodized at 15 V while on the TiAlZr sample anodized at 30 V a porous oxide layer was observed, denoting a transition from nanotubes to nanopores at higher voltage. All tests indicate that TiAlZr anodized at 30 V has greater resistance against corrosion compared to TiAlZr anodized at 15 V or bare TiAlZr sample.

Merit and demerit effects of silver nanoparticles in the bioperformance of an electrodeposited hydroxyapatite: nanosilver composite coating

For this research, TiAlZr specimens were covered with a hydroxyapatite–silver nanoparticles composite coatings (nAg-HA) prepared by pulse electrodeposition. The morphological texture of the nAg-HA nanoparticles on TiAlZr surface was investigated with scanning electron microscopy and energy dispersive X-ray spectroscopy. Electrochemical parameters from dynamic polarization tests performed in Ringer’s solution indicate better anticorrosive properties for the TiAlZr alloy after nAg-HA electrodeposition. Bacteriological experiments performed in vitro demonstrate the efficacy of TiAlZr implants coated with nAg-HA against the growth of Escherichia coli bacteria quantified in a 98 % inhibition of Escherichia coli growth. The biocompatibility tests regarding cell adherence, proliferation, and viability of coating (also by means of Reverse Transcription Polymerase Chain Reaction—RT-PCR) completed the characterization of the coating, enabling us to discuss the merit and demerit effects of Ag nanoparticles (nAg) effects on bioperformance. Based on experimental and literature data, the coating could be considered a passive–active structure.

Role of aluminum ion implantation on microstructure, microhardness and corrosion properties of titanium alloy

Ti–Al–Zr alloy was implanted with Al at cumulative doses between 1 × 10 17 and 1 × 10 18 ions/cm 2. The results indicate that the Al-implanted layers are ∼0.1 μm thick and are composed almost entirely of an amorphous layer. Implanted layer hardness is dose dependent and is increased by more than a factor of 4 for the high-dose implanted specimen when compared with that of the substrate material. The corrosion resistance of the sample was markedly improved after aluminum implantation.

Fabrication of Ti–Al–Zr alloy oxide nanotube arrays in organic electrolytes by anodization

We report the formation of self-organized Ti–Al–Zr alloy oxide nanotube arrays at different fluoride concentrations in formamide and glycerol electrolytes. The nanotube morphology is strongly influenced by the fluoride concentration, applied potential and reaction time. Titanium alloy (Ti–Al–Zr) oxide nanotube arrays with a length of about 6.13 μm, a pore diameter of 116 nm and wall thickness of 55 nm were prepared at 50 V for 24 h in formamide and glycerol mixtures (volume ratio 1:1) with addition of 1.0 wt% NH4F. The as-prepared nanotubes were amorphous and alloy oxide crystals appeared after annealing in air at 400 and 600 °C for 3 h.

Role of tantalum and nickel ion implantation on corrosion resistance properties of a Ti–Al–Zr alloy

Electrochemical behavior of Ti–Al–Zr implanted with nickel and tantalum ions and a co-implantation of them was investigated as a function of fluences. The polarization curves of the un-implanted and implanted Ti–Al–Zr were potentiodynamically measured in a hydrochloric acid solution. Electrochemical measurements revealed that nickel ion implantation significantly promoted the passivation of Ti–Al–Zr with an increase of fluence and the corrosion potentials resided in the passive region at fluences above 1 × 10 16 ions/cm 2. Tantalum ion implantation was effective in reducing the anodic current densities in the active and passive regions as fluences increased. On the other hand, the polarization curves of the co-implanted Ti–Al–Zr exhibited more stable passive behavior with low current densities. It was concluded that an excellent corrosion resistance of Ti–Al–Zr was achieved by complementary effects of nickel and tantalum ions co-implantation.

Surface modification of a Ti–Al–Zr alloy by niobium ion implantation

Surface modification of a Ti–Al–Zr alloy with niobium ion implantation is considered as a method to improve its tribological properties, particularly wear resistance and hardness. The ion implantation was carried out at fluences of 8×1016 and 4×1017 ions/cm2 with energy 108 keV. The tribological tests for the friction coefficients and wear rate were performed using a pin-on-disk tribotester with the load 60 mN. Glancing angle X-ray diffraction (GAXRD) and X-ray photoelectron spectroscopy (XPS) analyses were used to characterize the surface modification of the implanted samples. A significant improvement in the hardness and decrease in the friction coefficient have been found with increasing implantation fluences. In addition, the wear rates of the implanted samples exhibited a great reduction as compared with unimplanted samples. The effects of surface modification upon niobium ion implantation on the tribological properties of Ti–Al–Zr alloys were discussed in detail.

Surface characteristics and corrosion behavior of Ti–Al–Zr alloy implanted with Al and Nb

Ti–Al–Zr alloys were implanted with Al and Nb to doses ranging from 1 × 10 17 to 1 × 10 18 ions cm −2. The valence states of element on the sample surfaces were analyzed by X-ray photoelectron spectroscopy (XPS). Glancing angle X-ray diffraction (GAXRD) was employed on the as-implanted specimens to understand phase formation. X-ray diffraction (XRD) measurement revealed α-Ti on Al-implanted samples and (α + β)-Ti on Nb-implanted samples. The tendency was observed in increasing corrosion resistance from α- toward (α + β)-phase. In deaerated 5 M HCl, the ion-implanted Ti–Al–Zr surface containing Nb-stabilized β-phase was spontaneously passive, while Al-implanted surface displaying an active/passive behavior. In the aerated solution with pH = 10, all the implanted surfaces are passive. Enhanced reoxidation was confirmed on implanted surfaces by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analysis. The corrosion in the solution with pH = 10 was governed by a predominantly TiO 2 surface film. The cathodic kinetics was seen to affect the corrosion behavior in 5 M HCl.

Improvement of tribological behavior of a Ti–Al–Zr alloy by nitrogen ion implantation

Surface modification of a Ti–Al–Zr alloy with nitrogen implantation is considered as a method to improve its tribological properties especially wear and hardness. The implantation was carried out at fluences range from 1 × 10 16 to 1 × 10 17 ions/cm 2 and energy 65 keV. The tribological tests for the friction coefficients and wear were made on a pin-on-disk tribotester with the load 60 mN. Glancing angle X-ray diffraction (GAXRD) and X-ray photoelectron spectroscopy (XPS) analyses were performed to obtain surface characterization of the implanted sample. The unimplanted and implanted samples were also annealed at 500 °C in order to understand the influence of annealing on the tribological properties of Ti–Al–Zr. The hardness showed significant improvement at the higher fluence. After annealing at 500 °C, the friction coefficient exhibited a relative decrease for the nitrogen-implanted samples. In addition, the wear rates of the implanted samples exhibited a great decrease after annealing at 500 °C. Nature of the surface and reason for the variation and improvement in wear resistance were discussed in detail.

Surface characterization and corrosion resistance of Ti–Al–Zr alloy by niobium ion implantation

The aim of this paper is to study the effect of niobium ion implantation on corrosion resistance and phase formation on the implanted surfaces of Ti–Al–Zr alloy. Niobium ion was implanted into Ti–Al–Zr alloy at energy of 60 keV using a 150 keV accelerator at different fluences ranging from 5 × 10 16 to 4 × 10 17 ions/cm 2, respectively. Electrochemical studies have been conducted in a simulated reactor environment with pH = 10 in order to determine the optimum fluence that can give good corrosion resistance. X-ray photoemission spectroscopy (XPS) and glancing angle X-ray diffraction (GAXRD) were employed to examine the phase formation of niobium ion implanted samples. Niobium implantation into the alloy resulted in precipitation of NbTi 4 and Nb precipitates. Microhardness measurements revealed an increase after niobium implantation into the samples. It was found that niobium implantation increases the corrosion resistance. Nature of the surface and reason for the variation and improvement in corrosion resistance are discussed in detail.

Phase formation in nitrogen ion implanted Ti–Al–Zr alloy and modification of corrosion property

In the present investigation, surface modification of Ti–Al–Zr alloy with nitrogen ions is considered as a method to improve its performance with respect to corrosion. Nitrogen ions were implanted on Ti–Al–Zr alloy at an energy of 65 keV at different doses between 1 × 10 16 and 1 × 10 17 ions/cm 2. The valence states of nitrogen, titanium and carbon on the sample surfaces were analyzed by X-ray photoemission spectroscopy (XPS). Glancing angle X-ray diffraction (GAXRD) was employed on the as-implanted and annealed specimens to understand phase formation with increasing doses and annealing temperatures. The implanted samples were subjected to electrochemical study in a solution with pH = 10 in order to determine the optimum dose that can give good corrosion resistance in a simulated nuclear reactor condition. The passive current density and area of the repassivation loop were found to decrease as the doses increased. Nitrogen ions implantation enhanced the passivation and reduced the corrosion kinetics of the alloy surface with increasing tendency for repassivation. The corrosion resistance of as-implanted and annealed samples was better than that of as-implanted samples. Nature of the surface and reason for the variation and improvement in corrosion resistance were discussed in detail.

Hydrogen embrittlement of a TiAlZr alloy evaluated by impact test method

Abstract The characteristics of hydriding and hydrogen embrittlement of a Ti Al Zr alloy were evaluated by the impact test method. The results indicated that the hydrides in Ti Al Zr alloy formed as platelets and were identified as face-centered cubic δ-hydride. At room temperature, the specimen showed great sensitivity to embrittlement in ductility by hydrogen. The hydrides formed promoted the crack propagation in the presence of stress, leading to the cleavage failure mode. The impact toughness decreased dramatically with increasing hydrogen concentrations, indicated that the critical hydrogen concentration required to embrittle the alloy might be lower than 300 ppm.

TEM observation of oxide scale formed on a Ti–Al–Zr alloy oxidized at 360°C in alkaline steam

Ti–Al–Zr alloy has been oxidized at 360°C in alkaline steam at a pressure of 10.3 ± 0.7 MPa. Cross-sectional transmission electron microscopy (TEM) observations indicated that the oxide scale of Ti–Al–Zr alloy was composed of outer and inner subscales, in which the outer layer consists of anatase-TiO2 and the inner layer a mixture of TiO and Ti2O. The thickness of the Ti2O, TiO and anatase-TiO2 were approximately 50, 100 and 400 nm, respectively. These results were confirmed by X-ray energy dispersive spectrometry (EDS) measurements. The enhanced corrosion of titanium alloys in LiOH solution is attributed to a high hexagonal Ti2O to tetragonal TiO2 phase transformation rate induced by the substitution of Li+ for Ti4+ in the oxide layer.

Synthesis of ternary L10 compounds of Ti–Al–Zr system and their mechanical properties

Abstract A number of ternary Ti–Al–Zr alloys with different compositions around the binary γ-TiAl (L1 0 structure) were prepared and annealed at 1273 K for 10 h followed by quenching. Almost single γ-phase is produced in a rather wide composition region of Al 50 (Ti 50− x − y Al x Zr y ) with 0 ≤ x ≤ 15 and 0 ≤ y ≤ 15. Both lattice parameters, a and c increase with increasing Zr concentration due to larger atomic radius of Zr than those of Al and Ti. The c / a ratio of Al 50 Ti 50− x Zr x decreases towards unity as x increases. The Vickers hardness value increases rapidly with increasing Zr substitution. Compression tests at high temperatures for Al 50 Ti 50− x Zr x and Al 55 Ti 45− x Zr x with x = 5, 10 or 15 showed that except for Al 50 Ti 45 Zr 5 , specimens underwent brittle fracture below 1000 K; only the Al 50 Ti 45 Zr 5 specimens exhibited a considerable plastic strain at all the test temperatures, and the temperature dependence of the yield stress showed a peak at 973 K with the peak yield stress as high as 1000 MPa, indicating a possible application of this ternary alloy.

Effects of hydrogen on the mechanical properties of Ti–Al–Zr alloy

The distribution and structure of hydrides in the alloy and the effects of hydrogen on the mechanical properties of the alloy have been studied using electron microscope and mechanical test systems. The results indicated that the hydrides in Ti–Al–Zr alloy formed as platelets and had the fcc δ-structure with lattice parameter a = 0.438nm. The alloy showed different sensitivities to the hydrogen embrittlement in tensile tests and impact tests. Hydrogen and formed hydrides induced hardening and caused slight loss in the ductility examined in the tensile tests. However, the impact toughness decreased dramatically with increasing hydrogen concentrations, indicated that the critical hydrogen concentration required to embrittle the alloy might be lower than 700wppm. The difference in ductility measured in the two test methods were thought being resulted from the stress assisted hydrogen diffusion and the hydride formation in the impact specimen and in the necking area of a tensile specimen. The results have been discussed extensively.

Characteristics of hydriding and hydrogen embrittlement of the Ti–Al–Zr alloy

The characteristics of hydriding and hydrogen embrittlement of the Ti–Al–Zr alloy were evaluated. The amount of hydrogen absorbed into the alloy at 500 °C was continuously monitored using a hydrogen pressure measurement. The rate of decrease in hydrogen pressure indicated a high absorption rate of hydrogen into the alloy, following a linear rate law. X-ray diffraction studies showed the formation of δ-phase titanium hydride (TiH 1.97) after hydriding. At room temperature, the alloy showed much sensitivity to embrittlement in ductility by hydrogen. The δ-hydrides in the grain boundaries promoted the crack propagation in the presence of stress, leading to the cleavage failure mode. However, the tensile strengths were almost independent of the hydrogen content up to 1174 ppm. It is thus concluded that the δ-hydride acts to decrease the ductility without affecting tensile strengths.

Effects of annealing on tensile property and corrosion behavior of Ti–Al–Zr alloy

The effects of annealing on the tensile property and corrosion behavior of Ti–Al–Zr alloy were evaluated. The annealing in the temperature range from 500 to 800 °C for 1 h induced the growth of the grain and the precipitate sizes. The results of tensile tests at room temperature showed that the strengths and the ductility were almost independent of the annealing temperature. However, the results of corrosion test in an ammonia aqueous solution of pH 9.98 at 360 °C showed that the corrosion resistance depended on the annealing temperature, and the corrosion rate was accelerated with increasing annealing temperature. Hydrogen contents absorbed during the corrosion test of 220 days also increased with the annealing temperature. It could be attributed to the growth of Fe-rich precipitates by annealing. It is thus suggested that the lower annealing temperatures provide the better corrosion properties without degrading the tensile properties.

Hydrogen-Induced Amorphization in Ti-Al-Zr Compounds with D0<SUB>19</SUB>, B2 and FCC Structures

Structural changes and the hydrogen content in pseudobinary Ti3Al–Zr3Al, i.e., Ti1−x−yAlyZrx alloys (y=0.25, 0.30 and 0.35) by hydrogenation were examined with a powder X-ray diffractometer (XRD) and a hydrogen analyzer. Single-phases with the D019 and the B2 structures were formed in the homogenized alloys, while an fcc phase coexisted with the B2 phase. These D019, B2 and fcc phases changed into an amorphous phase by hydrogenation below 573 K. This is the first report of hydrogen-induced amorphization (HIA) by hydrogenation of a single-phase bcc type (B2) alloy. Furthermore, crystallization behavior of the hydrogen-induced amorphous Ti–Al–Zr alloys was investigated by a differential scanning calorimeter (DSC) and XRD.