α型チタン合金Ti-5Al-2.5Snのβ処理組織におよぼす冷却速度の影響

概要

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Effect of cooling rates after β treatment on microstructures in an a titanium alloy, Ti-5Al-2.5Sn, is examined. At the cooling rate of 300℃/s, no grain boundary α phase is observed and lath type of plate structure is formed throughout the specimen. In the lath plates, highly dense dislocations are included, and Fe-enriched β phase is retained between lath plates, which indicates that both shear and diffusional components of transformation operate during cooling. At the lower cooling rate (≦4℃/s), structural dislocations other than β phase are observed between α plates. It is considered to be due to the coalescence of two adjacent a plates which have slightly different crystallographical orientations each other. At the cooling rate of 0.1℃/s, ring-like diffuse streaks and extra spots which are related to ω phase are detected in the diffraction pattern of Fe-enriched β phase. Furthermore, aging treatment at 550℃ for 24 h after cooled from β region at the cooling rate of 300℃/s produces the refined equiaxed structure containing sub-grains, recrystallized grains and β phase at the triple points of α (sub-) grain boundaries.
社団法人日本鉄鋼協会の論文
1991-12-01