Unidirectional solidification of ternary eutectic Al-Ni-Si alloys

Abstract

Two monovariant alloys — type I (Al/6%Ni/0–2.5%Si) and type II (Al/12%Si/0–1.5%Ni) — and the ternary (Al-Ni-Si) eutectic have been studied. For the type I alloys particular attention was given to the effect of silicon concentration on the microstructural stability of the binary eutectic Al-Al 3Ni. Three distinct morphologies were observed, according to the solidification parameters. These were: well-aligned; aligned/cellular transitional; and cellular. The morphology of the silicon phase in the type II alloys was found to be very sensitive to any change in the solidification rate. The presence of very small amounts of nickel resulted in the formation of Al 3Ni; its growth was influenced by the kinetics and growth of the silicon phase. In the ternary eutectic, two of the three phases — Al 3Ni and Si — developed rod-like morphologies at the lowest solidification rates, with almost planar solid/liquid interfaces. As in the type II alloys, the silicon phase was sensitive to the solidification rate and it affected the growth of the Al 3Ni.