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Microstructural features of the hydrogenation-dehydrogenation process in Ti alloys
Published online by Cambridge University Press: 31 January 2011
Abstract
Temporary alloying of Ti alloys with hydrogen is used to modify microstructure and hence enhance mechanical properties. In the present work the influence of the thermal history of the Ti–6Al–4V alloy on the final microstructure was studied. Two different kinds of microstructures were investigated: (a) as-hot isostatic pressed (HIP) having an α + β microstructure; (b) β-solution-treated and subsequently quenched (α'-microstructure). After each stage of the hydrogenation-dehydrogenation (HDH) process the material was analyzed by optical, scanning electron and transmission electron microscopy, and by x-ray diffractometry. It was found that fcc (γ) hydrides precipitate in both the α and the α' matrix. The orientation relationships were found to be the same in both cases. Hydrides precipitate from the β-phase when the hydrogen content of the alloy is sufficiently high. The minimum concentration that still led to precipitation was 1.4 wt. % H. The β/γ orientation relationship was determined. The HDH process resulted in either of two structures: (1) a fine, broken-up microstructure containing a fine mixture of α' + (α + β) when the starting microstructure was α', or (2) a modified α + β microstructure containing fine α and β precipitates and a high density of microdefects within the primary α in the as-HIP α + β microstructure specimens.
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