微細ラメラ粒組織を有するTiAl基合金の反応焼結法による創製とその機械的性質に及ぼす粒径の効果

Abstract

A fully lamellar structure with the average grain size between 28 and 270 μm was achieved by reactive sintering in Ti-43.4Al-1.6Mn (mol%) alloy with TiB2 particulates. Using the alloy with a fully lamellar structure, the effect of grain size on the strength, ductility and fracture was investigated at both room temperature and 1073 K.At room temperature, the yield strength obeys the Hall-Petch relation, and the Hall-Petch parameter, ky, is found to be larger than that of the single phase γ alloys reported previously. When TiB2 content is lower than 5 vol%, the fracture strength also obeys the Hall-Petch type relation and the elongation increases with a decrease in grain size, suggesting that the critical stage of fracture is associated with the nucleation of the crack based upon a pile-up model.At 1073 K, when the grain size is smaller than 90 μm, the yield strength decreases with a decrease in grain size, and the elongation exhibits a higher value than that at room temperature. The maximum peak of the tensile strength appears at the grain size of about 60 μm.All these results indicate that the suitable grain sizes are in the range from 40 to 90 μm in considering the balance of ambient and elevated tensile properties.