E. Tal-Gutelmacher

Absorption/desorption behavior of hydrogen and deuterium in a Pd-coated Zr-based amorphous alloy

Palladium (Pd) coating was found to enhance significantly the absorption/desorption behavior of hydrogen in amorphous Zr69.5Cu12Ni11Al7.5, thereby improving the applicability of this alloy to hydrogen storage systems. This paper demonstrates the different characteristics of deuterium/hydrogen absorption/desorption in this Pd-coated metallic glass. Pd-coated amorphous ribbons were electrochemically charged with hydrogen or deuterium to various concentrations. Absorption and desorption characteristics were determined by means of a hydrogen determinator and thermal desorption spectroscopy (TDS), respectively. Hydrogen effects on the thermal stability and crystallization characteristics were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The hydrogen uptake was found to be twice faster than that of deuterium. Hydrogen-induced phase transformations, however, might prevent the use of this alloy for hydrogen storage applications.

Irreversible Hydrogen Trapping in Welded Beta-21S Titanium Alloy

β - 21S titanium alloy is ranked among the most important advanced materials for a variety of technological applications, due to its combination of a high strength/weight ratio, good corrosion behavior and oxidation resistance. However, in many of these technological applications, this alloy is exposed to environments which can act as sources of hydrogen, and consequently, hydrogen-induced cracking and property degradation, hydrogen-induced ductile-to-brittle transition associated with a change in the fracture mode from ductile, micro-void coalescence to brittle, cleavage have to be considered[1, 2, 3, 4]. In the aged β-21S alloy, the susceptibility to hydrogen induced cracking and the decrease in the alloy’s strength has been attributed to the -phase precipitated during the aging and the hydrogen-induced stabilization of the β-phase[1, 2, 5]. Hydrogen-induced intergranular cracking in the cathodically pre-charged β-21S alloy was significantly influenced by the preferential α precipitation at β grain boundaries[5]. Even without hydriding, the α-β interfaces could provide trapping sites and the accumulation of hydrogen at these interfaces could result in fracture. Pound[6] revealed that in aged β-Ti alloys the relationships among the trapping constants, resistance to hydrogen embrittlement and grain boundary are critical in determining the role of trapping in hydrogen embrittlement of these alloys.

Hydrogen Behavior in GTA Welded Ti-6Al-4V and Beta-21S Aerospace Applicative Titanium Alloys

Ti-6Al-4V and β-21S (Ti-15Mo-3Al-3Nb-0.3Si, wt%) titanium alloys were exposed to a hydrogen-containing environment, introduced by Gas-Tungsten Arc welding via a mixed Ar + 5% H2 shielding gas. The different characteristics of hydrogen absortion/desorption behavior and trapping in the welded Ti-6Al-4V and β-21S alloys were studied by means of thermal desorption spectroscopy (TDS). Thermal spectra analysis is supported by data from a variety of other experimental techniques, e.g., Leco hydrogen determinator and microstructure investigations. In the specimens welded in hydrogen-containing environment, no cracking was observed. However, the complex process of hydrogen desorption was found to be significantly affected by the microstructure developed in the alloys after welding. The unique microstructural morphology, the presence of potential irreversible trapping sites and phase transitions (oxide dissociation) were considered to be the potential parameters affecting the hydrogen desorption behavior from the alloys.

Hydrogen's Absorption/Desorption Behavior in Gaseous-Phase Charged Duplex-Annealed Ti-6Al-4V Alloy

Ti-6Al-4V alloy has proven to be technically superior and cost-effective materials for a wide variety of aerospace, industrial, marine and commercial applications. The mechanical properties of Ti-6Al-4V are very sensitive to the microstructure obtained after the thermo-mechanical treatment. The duplex structures provide good tensile ductility, fatigue strength, resistance to microcrack growth and crack initiation, and are often used in demanding fatigue critical tasks. However, although Ti-6A-4V is considered to be reasonably resistance to chemical attack, severe problems can arise when it comes in contact with hydrogen-containing environments due to its susceptibility to hydrogen embrittlement. The objective of this paper is to investigate the absorption and desorption behavior of external hydrogen on a duplex-annealed Ti-6Al-4V alloy. While investigating the desorption profile, we seek to better understand the thermodynamics and the kinetic nature of the interaction between traps and hydrogen atoms, with specific emphasis on the investigation of the impact of these interactions on the microstructure of the studied aerospace applicative titanium alloy. In order to achieve these goals, thermal desorption spectroscopy (TDS) was applied and the data obtained from this analysis was supported by a variety of other experimental techniques, such as LECO hydrogen determinator, XRD and microstructure investigations by means of optic and electronic microscopy. Hydrogen was found to influence significantly the microstructure of the alloy. The process of hydrogen evolution was found to be a very complex process, being affected mainly by the phase transformations that may occur during the thermal analysis.

High Fugacity Hydrogen Effects in Beta-21S Titanium Alloy

Beta-21S titanium alloy is ranked among the most important advanced materials for a variety of technological applications, due to its combination of a high strength/weight ratio, good corrosion behavior and oxidation resistance. However, in many of these technological applications, this alloy is exposed to environments which can act as sources of hydrogen, and consequently, severe problems may arise. The objective of this paper is to investigate the influence of high fugacity hydrogen on Beta-21S alloy in as-received (mill-annealed and hot-rolled) condition. Hydrogen effects on the microstructure are studied using X-ray diffraction and electron microscopy, while the absorption and desorption characteristics are determined respectively by means of a hydrogen determinator and thermal desorption spectroscopy. Preliminary results at room temperature revealed hydrogen-induced straining and expansion of the lattice parameters. However, neither second phases formation (hydrides), nor hydrogen-induced cracking, were observed after hydrogenation. The main characteristics of hydrogen absorption/desorption behavior, as well as hydrogen-induced microstructural changes in both microstructures are discussed in detail.