Filtern
Dokumenttyp
Sprache
- Englisch (10)
Referierte Publikation
- nein (10) (entfernen)
Schlagworte
- Beta-21S (3)
- Hydrogen desorption (3)
- Titanium alloys (3)
- Thermal Desorption Spectroscopy (TDS) (2)
- AZ31B (1)
- Corrosion behavior (1)
- Hydrogen embrittlement (1)
- Microstructure (1)
- TIG welded (1)
- Ti-6Al-4V (1)
Gas tungsten arc welds made on wrought magnesium AZ31 plate have
been characterized for corrosion in saline solution (3.5% NaCl). Microstructural
changes induced by the welding process resulted in different
environmental behaviour of each zone (BM-base metal, HAZ-heat affected
zone and FZ-fusion zone). The faster kinetics of corrosion in FZ and especially
HAZ are attributed to (a) the coarse microstructure, consisting of
large grains, and (b) very small amounts of ß-phase in the grain boundaries.
Also, hardness traverses have shown that these zones are weaker
than the base metal. Based on the significant effect of grain size on strength
in magnesium alloys, the weld metal grains have been systematically refined
using controlled oscillation during welding, and by adding a grain
refiner to the weld pool. Detailed microstructure analyses have been carried
out and the relationships between corrosion behaviour, mechanical
properties and microstructure (grain refinement and second-phases formation)
are highlighted.
Hydrogen-assisted cracking (HAC) or hydrogen embrittlement (HE) are the most commonly used terms to describe a time-dependant failure process, characterized by mechanical properties degradation, mainly ductility reduction, and a change in the fracture mode. With almost no direct techniques for observing atomic-scale events at crack tips in bulk specimens, HE/HAC mechanisms are deduced mainly from fractography, microscopic investigation of microstructure changes, surface-science observations, and atomistic or continuum modeling. This paper addresses to HE/HAC mechanisms into two different systems; hydride-forming and non-hydride forming materials. As a representative example of the hydride-forming systems, the discussion focuses on the hydrogen-induced second phase formation (e.g. hydrides) phenomena in titanium based alloys. Due to the large differences in the behavior of hydrogen in α and β phases of titanium, the susceptibility of titanium-based alloys to the various forms and conditions of hydrogen embrittlement can vary markedly. The microstructural changes and hydrogen-induced second phase formation due to exposure at various charging conditions, as well as the difference in hydrogen absorption/desorption behavior as a function of the prior microstructure of titanium alloys, are highlighted. In non-hydride forming materials, where as representative examples stainless steels are chosen, the paper concentrates on the qualitatively same phenomena of hydrogen-induced second phase embrittlement. The phase transitions related to hydrogen-induced cracking, the hydrogen related failure sequences and fracture modes in austenitic and supermartensitic stainless steels and a potential modeling of hydrogen-assisted cracking in these structural metallic materials are discussed.