β rich α-β型チタン合金 Ti-6Al-2Sn-4Zr-6Mo の組織と機械的性質(<特集>チタンおよびチタン合金)

概要

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The Effect of microstructures in mechanical properties of β rich α-β titanium alloy Ti-6Al-2Sn-4Zr-6Mo was investigated. The β phase formed at the solution temperature above 900℃ transformed into the α" (orthorhombic martensite) phase with retained β phase by quenching treatment, but transformed into the acicular α phase with the retained β phase after slow cooling. Solution treatment in the temperature range between 825℃ and β transus temperature (952℃) and aging (STA) improved the tensile properties. But STA materials showed the lower fracture toughness than 80 kgf/mm^<3/2> on account of the presence of the fine acicular α grains between primary α grains. Double solution treatment and aging (STSTA) improved the fracture toughness. The volume fraction of primary α grains was optimized by first solution treatment and second solution treatment controlled the shape of the secondary acicular α grains. The higher fracture toughness in the STSTA materials appeared to be dependent upon the morphology of the secondary acicular α grains. The materials which were double solution treated at 940℃ for 1 h oil quenching (OQ) and at 830℃ for 2 h air cooling (AC) and aged at 590℃ for 6 h AC, possessed the following properties. Tensile strength : 121 kgf/mm^2 Tensile elongation : 14.4% Fracture toughness : 113 kgf/mm^<3/2>
社団法人日本鉄鋼協会の論文
1986-04-01