Al-CuAl<SUB>2</SUB>層状共晶と繊維状共晶とを組合わせた3元共晶合金の一方向凝固組織

Abstract

Ternary eutectic alloys, Al-CuAl2-NiCu3Al6, Al-CuAl2-FeCu2Al7 and Al-CuAl2-Si, consisting of Al-CuAl2 lamellar eutectics and Al-Al3Ni, Al-Al3Fe or Al-Si fibrous eutectics, were solidified unidirectionally over a wide range of rates. These microstructures are compared with those of concomitant binary eutectics and are discussed with reference to the term of entropy of fusion of each phases. In Al-CuAl2-Si ternary eutectics, Si grows with prefered 〈100〉 fiber texture as in Al-Si binary eutectics, though Al-CuAl2 lamellar are degenerated thoroughly. This is considered to come from the difference of entropy of fusion between Si and CuAl2, because the entropy of fusion of Si is higher than that of CuAl2. On the other hand, in Al-CuAl2-NiCu3Al6 ternary eutectics, Al-CuAl2 lamellae are maintained because the difference in the entropy of fusion between NiCu3Al6 and CuAl2 is smaller than that of Si and CuAl2. It may be concluded that with increasing entropy of fusion of the third phase, the influence of Al-CuAl2 on the Al-CuAl2 lamellae becomes greater.