α+β型チタン合金の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 two α+β titanium alloys, Ti-6Al-4V and Ti-6Al-6V-2Sn, is examined. From the microstructural examinations and hardness measurements, cooling rates are classified into three regions. In the first region (lower than 10℃/s in Ti-6Al-4V and 4℃/s in Ti-6Al-6V-2Sn), dependence of hardness on cooling rates is relatively small and a few dislocations are involved inside the transformed plates. In the second region (10∿300℃/s or higher cooling rates in Ti-6Al-4V, 4∿20℃/s in Ti-6Al-6V-2Sn), hardness strongly increase with the increase of cooling rates, and highly dense dislocations are included in the plates, although diffusion of solute atoms are expected. In the third region (higher than 20℃/s in Ti-6Al-6V-2Sn), hardness shows a constant and high value which is independent of cooling rates. In Ti-6Al-6V-2Sn cooled at the cooling rate of 300℃/s, there are quite many micro-twins or stacking faults in the acicular type of plates and little amount of diffusion is detected. It is considered that diffusional component and shear one of transformation mainly operate at the cooling rates in the first and third regions, respectively. At the cooling rates in the second region, both components operate competitively during cooling.
社団法人日本鉄鋼協会の論文
1991-09-01