화학공학소재연구정보센터
Journal of Materials Science, Vol.33, No.17, 4365-4374, 1998
Effects of composition on microstructures of rapidly solidified Ni-Al alloys
Microstructures of melt-spun NI-AI alloys with compositions from 61-85 at % Ni were studied by means of transmission electron microscopy, X-ray diffraction analysis and optical microscopy. The microstructures of as-quenched ribbons exposed to cooling rates of the order of 10(6) Ks(-1) reflect the transition from primary beta-NiAl to gamma-Ni solidification with increasing nickel content. In 70 at % Ni alloy ribbons, martensitic NiAl grains were detected near the wheel-side surface contrasting with anomalous and lamellar eutectic microstructure in the top part. Directly ordered Ni3Al grains with single (or large) antiphase domains (APDs) and a minor eutectic fraction were observed in 75 at % Ni alloy ribbons. Samples containing 80 at % Ni exhibit mainly single-phase Ni3Al grains with 10-20 nm sized APDs indicating sequential ordering. Weak L1(2) ordering was even detected in 85 at% Ni ribbons which displayed ordered antiphase zones of 1 nm size. Disordered gamma-(Ni) films on grain boundaries can be discounted for 80 at % Ni ribbons, but occurred near the top of 85 at % Ni samples. The results are explained in terms of the reassessed Ni-Al phase diagram employing recent corrections near to the Ni3Al composition and new results on phase formation in undercooled Ni-Al melts.