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Hydride Precipitation Behavior in α+β Ti-6Al-4V Alloy(Materials, Metallurgy & Weldability)

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An investigation has been made into the hydrogen diffusion and hydrides precipitation behavior of α+β Ti-6Al-4V alloy by means of X-ray diffraction method, internal friction measurement and transmission electron microscopy. The hydrogenation was made by cathodic charging at current densities of 50A/m^2, 500A/m^2 and 4200A/m^2. As the alloy was hydrogen-charged, the peak of α phase by X-ray diffraction line profile was hardly shifted, but that of β phase was shifted to the low angle side. d_<200> spacing of β phase increased with increasing the charging time and then became constant value. It means that hydrogen was mainly diffused to the β phase and then solutionized to the solubility limit. This tendency was corresponded to the peak at about 80 K in the internal friction curves. And the peak at 80 K was clear to be Snoek peak. Before charging, X-ray diffraction line profile showed only α phase and β phase peak. The new peak occurred at 2θ=60.9 (π/180) rad., 92.8 (π/180) rad. so on, as the alloy was cathodically charged. The peak height increased with increasing the hydrogen-charging time, and increasing the charging current density. It means that the peak is due to the hydride precipitation. On the basis of X-ray diffraction line profiles, the volume fraction of α phase decreased with increasing the volume fraction of the hydrides, though that of β phase hardly changed, in the case of low current density of cathodic charging. It was confirmed by transmission electron microscopy. But in the case of high current density, both volume fraction of α phase and that of β phase decreased with increasing that of hydrides. It means that hydrides precipitated both in the α phase at α/β interface, and in the β phase. It was confirmed by transmission electron microscopy.



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