Maco/Micro Studies of Hydrogen Embrittlement Mechanisms in Titanium and Aluminum Alloys.

摘要

Systematic studies of environmental effects on fracture in two alpha/beta titanium alloys, one beta titanium alloy and 7475 aluminum alloys have been accomplished. Ti-6Al-6V-2Sn has been tested for its hydrogen-induced cracking behavior under sustained loads. The influence of frequency and microstructure on fatigue crack growth have also been studied. Fatigue crack growth in Ti-5A1-4Mo, as a function of hydrogen content, temperature and Widmanstatten colony size, was then studied. Mechanical data have been obtained along with TEM and SEM characterizations. Modelling for fatigue thresholds has been attempted to explain dislocation, microstructure and hydrogen effects. Ti-30 Mo has been studied for effects of hydrogen on dislocation dynamics, cleavage fracture stress and fatigue crack propagation. Fractography (SEM) has been used to characterize the fracturing processes and modeling attempted to explain the hydrogen effects. Hydrogen effects in aluminum alloys are not as obvious as those in titanium alloys. Both cathodic and gas-phase charging did not significantly increase the hydrogen content of this material. Mechanical properties did not seem to change decisively after hydrogen charging. But the lack of a macroscopic effect does not preclude a hydrogen mechanism in environmentally assisted events. (Author)