Hydrogen In Titanium Alloys Research Articles

Hydrogenation Behavior of Ti6Al4V Alloy

Abstract The hydrogenation behavior of Ti6Al4V alloy was investigated at different hydrogenation temperatures, holding time and hydrogen pressures. The distribution of hydrogen in titanium alloy was studied by OM. Results show that the hydrogen content of Ti6Al4V alloy is controlled by hydrogenation temperature, hydrogen pressure and holding time. Hydrogen content increases first and then decreases with the increasing of hydrogenation temperature. Hydrogen content increases linearly with the increasing of hydrogen pressure. The process of hydrogenation is diffusion of hydrogen into titanium alloy, and the distribution of hydrogen becomes uniform with the increase of holding time.

Effect of a High-Temperature Hydrogen Treatment on a Microstructure and Surface Fracture in Titanium Ti-6Al-4V Alloy

Influence of hydrogen on the structure of titanium alloys is a complex phenomenon, depending on the circumstances, may be negative or positive [1,2]. The presence of hydrogen in titanium alloys usually results in degradation of their microstructure and properties, as well promote some undesirable effects such as hydrogen corrosion and hydrogen embrittlement [3]. Positive nature of the effects of hydrogen on the properties of titanium alloys is manifested in the high temperature hydrogen treatment (HTM - Hydrogen Treatment of Materials), where hydrogen is temporary alloying component [4-9]. This is possible because of the high values of diffusion coefficients can be easily introduced into the titanium and it just as easily removed. Titanium and its alloys show the absorbability of almost 60 at. % of hydrogen at 600°C. The limit hydrogen of solubility in Tiα is very low and does not exceed 0.05 at. % at room temperature. The limit hydrogen of solubility in Tiβ is much higher and its maximum value is 48 at. %. Since the beginning of the titanium industry, a great deal of attention has been paid to control the hydrogen content at titanium products – above 0.2 ppm. The paper presents the results of the possibilities of hydrogen using as a temporary alloying element in Ti-6Al-4V alloy. Treatment of hydrogen alloy consisted of three stages: hydrogenation in hydrogen gas atmosphere at 650 °C, a cyclic hydrogen-treatment (3 cycles 650 °C to 250 °C) and a dehydrogenation in vacuum (550 °C). It was shown that hydrogen affects appreciably changes the microstructure of surface layer of the tested titanium alloy. The aim of this study is thus to determine the effect of hydrogen on the two-phase microstructure, hardness, and surface fracture of the titanium alloy Ti-6Al-4V due to high-temperature hydrogen treatment.

Positive Effect of Hydrogen Treatment in Titanium Ti-6Al-4V Alloy

Positive nature of the effects of hydrogen on the properties of titanium alloys is manifested in the high temperature hydrogen treatment (HTM - Hydrogen Treatment of Materials), where hydrogen is temporary alloying component. This is possible because of the high values ​​of diffusion coefficients can be easily introduced into the titanium and it just as easily removed. Titanium and its alloys exhibit a high affinity for hydrogen absorption capacity, about 60% at. hydrogen at 600 °C. The hydrogen in titanium alloy is present in the form – an interstitial solution or titanium hydride. Since the specific volume of titanium hydride is about 13 ÷ 17% higher compared to α phase, it is high stress in the crystal lattice of this phase leads to local plastic deformation and large deformation phase. The paper presents the results of the possibilities of hydrogen using as a temporary alloying element in Ti-6Al-4V alloy. Treatment of hydrogen alloy consisted of three stages: hydrogenation in hydrogen gas atmosphere at 650 °C, a cyclic hydrogen-treatment (3 cycles 650 °C or 950 °C to 250 °C) and a dehydrogenation in vacuum (550 °C). It was shown that hydrogen affects appreciably changes the microstructure of surface layer of the tested titanium alloy. The aim of this study is thus to determine the effect of hydrogen on the two-phase microstructure, hardness, and corrosion resistance of the titanium alloy Ti-6Al-4V due to high-temperature hydrogen treatment.

Sources of uncertainties in prompt gamma activation analysis

Two prompt gamma-ray activation analysis (PGAA) facilities at the NIST Center for Neutron Research have been used routinely to perform elemental analyses of a variety of materials. Results from these analyses are usually expressed as mass fraction values with expanded uncertainties. The expanded uncertainty consists of the combined uncertainty multiplied by the appropriate coverage factor (k) required to achieve a 95% confidence interval. The combined uncertainty includes the uncertainties associated with preparation, irradiation, and γ-ray spectrometry of samples and standards, and corrections for γ-rays from the background or blanks where necessary. To determine the combined uncertainty, each component of uncertainty associated with each variable and constant in the basic measurement equation is evaluated. In this paper we present the PGAA measurement equation, a description of the potential sources of uncertainty for each component of the equation, and three examples of uncertainty evaluation. The examples are for determination of H in standard reference material (SRM) 2454, hydrogen in titanium alloy using the cold neutron PGAA facility, Cd in SRM 2702 Inorganics in Marine Sediment using the original thermal neutron PGAA facility, and N in SRM 3244 Ephedra-Containing Protein Powder using the recently designed thermal neutron PGAA facility.

Distribution and thermal desorption behavior of hydrogen in titanium alloys immersed in acidic fluoride solutions

The distribution and thermal desorption behavior of hydrogen in alpha titanium (commercial pure titanium) and beta titanium alloy (Ti–11.3Mo–6.6Zr–4.3Sn) immersed in acidic fluoride solutions (pH 5.0, 25 ± 2 °C) have been investigated. For alpha titanium, most of the hydrogen absorbed in the fluoride solution existed as titanium hydride within approximately 50 μm from the surface of the specimen. The local hydrogen concentration in the vicinity of the surface was evaluated above 5000 mass ppm. Hydrogen thermal desorption was observed in the temperature range from 200 to 700 °C. It is likely that the desorption at a low temperature resulted from the dissociation of the hydride, whereas that at a high temperature was caused by hydrogen strongly trapped in matrix defects induced by hydride formation. For the beta titanium alloy, the absorbed hydrogen diffused toward the center of the specimen without hydride forming. Hydrogen was almost uniformly distributed over the whole cross-section of the specimen, although hydrogen content was high at the surface layer of the specimen. Hydrogen desorption appeared in the range from 400 to 600 °C, implying that the absorbed hydrogen was mostly hydrogen in solution. The corrosion product (TiF 3) on the surface of the specimen caused the desorption temperature to rise more than 100 °C, suggesting the origin of the scatter of desorption behavior.

A method for determination of the diffusion coefficient of hydrogen in titanium alloys by chemical etching

We propose a model of absorption of hydrogen by titanium alloys in the process of chemical etching. We obtained a solution that describes the amount of absorbed hydrogen and its distribution in the metal as a function of the rate and time of etching. On the basis of the equations obtained, we developed a method for determination of the diffusion coefficient of hydrogen in a metal. The essence of the method is a sequential etching of a specimen in hydrogenated and nonhydrogenated solutions and determination of the amount of hydrogen which remains in the metal. The effective diffusion coefficients of hydrogen in titanium alloys with various structures are found.

Standards for Hydrogen in Titanium Alloy

ABSTRACTMass-fraction standards of dilute hydrogen in titanium alloy are prepared by direct reaction of the elements, and verified by cold-neutron prompt-gamma activation analysis. The procedure is applied to the production and characterization of Standard Reference Materials.

Determination of Hydrogen in Metals, Semiconductors, and Other Materials by Cold Neutron Prompt Gamma-Ray Activation Analysis

ABSTRACTCold neutron prompt gamma-ray activation analysis has proven useful for nondestructive measurement of trace hydrogen. The sample is irradiated in a beam of neutrons; the presence of hydrogen is confirmed by the emission of a 2223 keV gamma-ray. Detection limits for hydrogen are 3 mg/kg in quartz and 8 mg/kg in titanium. We have used the technique to measure hydrogen in titanium alloys, germanium, quartz, fullerenes and their derivatives, and other materials.

Determination of hydrogen in titanium alloys by cold neutron prompt gamma activation analysis

Cold neutron prompt gamma-ray activation analysis (CNPGAA) has proven useful for the analysis of hydrogen in titanium alloys. The analysis is nondestructive, measures the entire sample, and the results are independent of the chemical form of hydrogen present. We have used the technique to measure H mass fractions as low as 50 mg/kg in titanium-alloy jet-engine compressor blades and to measure hydrogen in standards for neutron tomography.

Redistribution of hydrogen in titanium alloys in deformation by compression

In their evaluation of titanium as a hydrogen storage medium the authors tested the effects of deformation and compression on hydrogen content, diffusion, and redistribution in alloys VT1-0 and VT14 following chemisorption of hydrogen. Distribution was studied before and after loading by laser-mass spectroscopy involving the fusion and evaporation in vacuum of microvolumes of metal by laser radiation. Results are tabulated.

Solubility of Hydrogen in Titanium Alloys. II. Blocking Models and Hole Size Considerations

AbstractAssuming a geometrical model with mutual (H‐H) blocking, for hydrogen dissolved in titanium and titanium alloys experimental data are compared. It is found that interstitial sites with pure titanium coordination only host hydrogen atoms. In alloys with bcc crystal lattices only tetrahedral interstitial sites are occupied, whereas in hep alloys both tetrahedral and octahedral interstitials host hydrogen. A linear relation is found which connects the partial molar absorption enthalpy ΔHOH and the partial molar excess absorption entropy ΔSE, OH at infinite dilution of dissolved hydrogen. The enthalpy of absorption ΔHOH can be rationalized as a function of interstitial hole size and an optimum hole radius of 47 pm is found for titanium and titanium alloys.

Solubility of Hydrogen in Titanium Alloys. I. The Solubility of Hydrogen in the System Ti1‐xGax, 0 ≦ x ≦ 0.25

AbstractApplying the manometric method, the solubility of hydrogen in alloys Ti1‐xGax was studied in the range 0 ≦ x ≦ 25; 5 · 10−5 ≦ pH2/bar ≦ 1; 773 ≦ T/K ≦ 1298. Within the given range of p and T the phase diagram of Ti1‐xGaxHr was investigated for 9 compositions x. In the range of solid solutions, 0 ≦ x ≦ 0.11, with increasing x the range Δr of the hcp phase α‐Ti1‐xGaxHr increases slightly, whereas the range of the bcc phase β‐Ti1‐xGaxHr, narrows strongly with increasing x. The width Δr of the two phase region α + β is nearly independent of x and the phase boundary between β‐phase and (β + γ) region shifts with decreasing Δr of the β‐phase to smaller r. In α‐T1‐xGaxHr the enthalpy of hydrogen solution ΔHH is practically independent of r but depends slightly on x, decreasing from ‐46.0 kJ mol−1 (x = 0) to ‐46.5 kJ mol−1 (x = 0.10). In the bcc phase β‐Ti1‐xGaxHr, ΔHH decreases markedly from ‐57 kJ mol−1 (r → 0) to ‐70 kJ mol−1 (r ⇌ 1). ΔHH is independent of the gallium content x within the limits of error. — Assuming a plausible blocking model for the occupancy of interstitial sites in the metal matrix by hydrogen, the excess entropies of dissolved hydrogen were evaluated. In α‐Ti1‐xGaxHr an increase of ΔSEH is found with increasing r from ‐55 JK−1 mol−1 (r→0) to ‐53 JK−1 mol−1 (r = 0.1). ΔSEH depends much stronger on r in β‐Ti1‐xGaxHr: ΔSEH = ‐70 JK−1 mol−1 (r→0); ΔSEH = ‐66.5 JK−1 mol−1 (r = 0.8). There is negligible influence of x on ΔSEH in both phases. — In the ordered hcp phase α2‐Ti3GaHr there is an increase of exothermicity compared to α‐Ti1‐xGaxHr. ΔHH (r → 0) is ‐51.3 kJ mol−1 for the ordered phase and it depends on r, increasing to ‐50 kJ mol−1 at r ⇌ 0.1. ΔSEH for this phase is independent of r, ΔSEH = ‐53 JK−1 mol−1. — Additional data on the hydrogen solubility in α‐Ti3Sb are given, resulting on more accurate thermodynamic data ΔHH, ΔSH, and ΔSEH.

Metrological characteristics of standard specimens for computeraided spectral determination of hydrogen in titanium alloys

Metrological characteristics of standard specimens for computeraided spectral determination of hydrogen in titanium alloys

Effects of hydrogen in titanium alloys on subcritical crack growth under sustained load

The susceptibility of three titanium alloys to subcritical crack growth in air under sustained load was determined as a function of hydrogen content. The alloys examined contained from 7 to 76 p.p.m. and included Ti6Al4V, Ti8Al1Mo1V and Ti4Al3Mo1V. Tests were conducted with 0.25-inch-thick, fatigue-precracked compact tension specimens. Crack-growth behavior was quite sensitive to hydrogen content; time to failure increased as hydrogen content was decreased, while the threshold stress intensity — defined as the highest initial stress intensity leading to failure within 1 month — appeared to attain a minimum value at an intermediate hydrogen content. Hydrogen content also was shown to have a significant effect on fracture toughness; dramatic improvements in toughness accompanied reductions in hydrogen content to low levels. The effects of hydrogen on toughness were independent of loading rates varying between 60 and 4600 k.s.i.-inch 1 2 per minute.

Diffusion of hydrogen in titanium alloys due to composition, temperature, and stress graduates

Diffusion of hydrogen in titanium alloys due to composition, temperature, and stress graduates

Diffusion of hydrogen in titanium alloys due to composition, temperature, and stress gradients

A theoretical and experimental study was conducted to determine the combined effects on interstitial diffusion in metals of gradients in interstitial concentration, in solvent composition, in stress, and in temperature. The theory consolidates relationships, some of which have been previously published. It is based on macroscopic irreversible thermodynamics, and is applicable to anisotropic or Isotropic materials. Experiments were conducted and literature analyzed to determine the numerical quantities required to predict the change in hydrogen distribution with time for pure and alloy titanium, where the solvent gradient, stress gradient, and temperature gradient are constant with time. The diffusion driving forces for solute gradient, solvent gradient, and stress gradient are related to the effect of each factor on hydrogen activity. In addition, the material property which determines the diffusion driving force of a stress gradient for anisotropic material is a matter tensor analogous to the scalar partial molal volume used for isotropic material. The experiments, conducted with commercially pure titanium and titanium alloy, 6A1-4V, consist of measuring the effect of alloy additions and stress on the hydrogen activity in solid solution and the dilatation effect of hydrogen. Stress states tested were tension, compression, and torsion. The measurements were made by exposing titanium and the alloy to hydrogen at temperatures from 600° to 800° C, and measuring the equilibrium hydrogen gas pressure at various solid solution hydrogen contents. Both materials were tested with and without stress. Tension decreased the activity, compression increased it, and torsion had no effect. This is consistent with the stress effect theory of Li, Oriani, and Darken. The stress effect corresponds to an apparent partial molal volume of 1.7 to 2.2 cm3/mol, depending on the alloy and hydrogen content.

Standard samples for the spectral determination of hydrogen in titanium alloys

Standard samples for the spectral determination of hydrogen in titanium alloys