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The influence of environment on fatigue crack growth behavior wasinvestigated in duplex titanium aluminides, and the hydrogen evolution kinetics wasanalyzed by thermal desorption spectroscopy. The tensile strength decreases in the order ofthe extent of the water molecule content in the environment. When cathodic charging isapplied, the fatigue crack growth rate becomes higher than in dry air, particularly in thehigher stress intensity factor range. The hydrogen evolution rate is increased by cathodiccharging, with lower temperature peaks and higher ones. The peaks at lower temperaturesare correlated with the decomposition of hydrides and de-trappiing of hydrogen frommicrostructural imperfections such as microvoids. As-received materials also show anevolution peak at a higher temperature, and the evolution rate is almost independent ofcathodic charging. In addition, the evolution rate at a high temperature (above 800°C) isincreased by cathodic charging. The hydrogen is considered to have an important role onfatigue crack growth acceleration.