水素吸蔵・時効・脱水素処理によるα+β型チタン合金の等軸超細粒化

Abstract

Titanium alloys can be hydrogenated with large amounts of hydrogen and dehydrogenated in vacuum at elevated temperatures. This paper aims at the equiaxed grain refinement of titanium alloys utilizing this phenomenon. Particular attention has been drawn to the control of two different types of dislocation structures introduced by the following treatments:(1) Precipitation of hydrides: On aging at relatively low temperature after solution treatment of hydrogenated titanium alloys, high density dislocations are introduced in the interior of hydrides and also in the surrounding region.(2) Martensitic transformation: On cooling from the β-phase or the α+β two phase region of hydrogenated titanium alloys, high density dislocations with uniform distribution are introduced in acicular martensites.The factor (1) gives rise to the localized dislocation structure which provides with heterogeneous nucleation sites for recrystallization, leading to the grain refinement. The factor (2) causes the subdivision of the, β-phase grain into fine martensite leaves with different variants, in each of which uniformly distributed dislocations of high density are introduced that may serve for the precipitation of hydrides.The combination of the two factors described above results in the grain refinement of the Ti-6Al-4V alloy containing large amounts of hydrogen, very different from the case simply utilizing the eutectoid trandormation. Specimens thus treated, exhibit ultra-fine equiaxed grains of about 1 μm diameter.