Nanoindentation creep mechanism of gradient ultrafine lamellar γ+Ni5Zr eutectic using electromagnetic levitation coupled with fall casting

A quaternary Ni₅₀Fe₂₀Cr₂₀Zr₁₀ eutectic alloy was designed based on the Ni–Fe–Cr alloy, and the gradient ultrafine lamellar γ+Ni₅Zr eutectic was achieved by means of electromagnetic levitation coupled with fall casting (EML-FC). The temperature field, the process of interface migration, microstructural characteristics and the nanoindentation creep property of the alloy were systematically analyzed. During the rapid solidification, since the conical surface served as the main heat dissipation channel, the solid-liquid interface moved from the conical surface towards the top of the cone axis. The gradual decrease in cooling rate from 10⁵ to 10³ K s⁻¹ along this direction led to the formation of the gradient ultrafine lamellar γ + Ni₅Zr eutectic with the size from 59 ± 12 to 140 ± 36 nm. The nanoindentation creep behavior and mechanism were analyzed by estimating the strain rate sensitivity and activation volume. As the interlamellar spacing of the eutectic decreased, the nanohardness and creep resistance of the alloy gradually increased owing to an increase in grain boundary density and the enhancement of coupling effect between dislocation and grain boundary. In addition, the creep behavior of alloy was sensitive to the loading rate. Increasing the loading rate led to an increase in strain rate sensitivity from 7.69 × 10⁻³ to 18.89 × 10⁻³ and a decrease in activation volume from 29 to 12 b³. This special eutectic structure and its improved nanohardness and creep resistance properties offered a potential opportunity to explore a new generation of alloys for the hot-end components of 972 K ultra-supercritical fossil-fired power plants.