Abstract
We report nano-precipitation induced hardening in Ni88.32Zr7.68Al4 ultrafine lamellar eutectic composite (UEC) and enhancement of yield strength from 1010 MPa to 1191 MPa upon annealing upto 120 min at 800 °C. The as-solidified microstructure of (Ni0.92Zr0.08)100−xAlx (x = 0 and 4 at.%) consists of micrometer sized γ-Ni dendrites homogeneously distributed in an eutectic (γ-Ni+Ni5Zr) matrix. High-temperature in-situ x-ray diffraction studies suggests that the coefficient of thermal expansion (CTE) of these eutectic phases are very close and the lamellar morphology is stable even up to 1000 °C without showing any hint of polymorphic transformation or spherodization. Transmission electron microscopic studies revealed addition of Al assists the evolution of ~1 vol% of 2–15 nm size L12–type precipitates in γ-Ni phase upon annealing in x = 4 exhibiting improved yield strength and bulk hardness. The hardening behavior of the UEC has been analyzed using extended Kocks–Mecking-Estrin model to explore the underlying mechanism of dislocation-precipitate interaction.
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