Strengthening ultrafine lamellar Ni-Zr-(Al) eutectic by precipitation hardening

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 degrees C. The as-solidified microstructure of (Ni0.92Zr0.08)(100-x)Al-x (x = 0 and 4 at.%) consists of micrometer sized gamma-Ni dendrites homogeneously distributed in an eutectic (gamma-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 degrees C without showing any hint of polymorphic transformation or spherodization. Transmission electron microscopic studies revealed addition of Al assists the evolution of similar to 1 vol% of 2-15 nm size L1(2)-type precipitates in gamma-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. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Hardening was observed in Ni-Zr-Al ultrafine lamellar eutectic composite via nano-precipitation, with significant enhancement of strength upon annealing and stable lamellar morphology up to high temperatures. Addition of Al facilitates the formation of small precipitates in the matrix, leading to improved material performance.