Thermal behaviour and microstructure evolution of new ternary eutectic alloy in Al-Cu-Si-Ni system

Eutectic alloys were fabricated from the quaternary Al-Cu-Si-Ni system via arc melting and suction casting. An invariant ternary eutectic reaction (alpha-Al+Si+theta-Al2(CuNi)) was found in the quaternary alloy system with a composition of Al67.2Cu24Si8Ni0.8 (wt%). The dissolution of Ni (similar to 1.7 at%) into tetragonal theta-Al2Cu takes place during this ternary eutectic reaction. Density functional theory (DFT) calculations show that the configurational entropy stabilises this level of randomly substituted Ni with Cu sites in the theta-Al2Cu lattice at high temperatures. The as-solidified eutectic microstructure exhibits a lamellar theta-Al2(CuNi) phase showing fragmented lamellar morphology with a lamellar thickness of 130 +/- 30 nm and Si exhibits fibrous mor-phology with a fibre diameter below 100 nm. The thermal stability of the Al-Cu-Si-Ni eutectic alloy after post-solidification annealing was investigated, and the thermal stability of the ternary eutectic micro-structure is better than the corresponding Al33Cu (wt%) binary eutectic microstructure. It was found that Ni solution in theta-Al2(CuNi) phase contributes to the thermal stability of this ternary eutectic microstructure and beta 2-Al3(CuNi)2 (beta 1-(Cu2.9Ni0.1)Al type, Fm-3 m) phase can transform from theta-Al2(CuNi) phase after annealing at different temperatures. The Al-Cu-Si-Ni eutectic alloy has excellent as-cast hardness together with thermal stability. It is potentially valuable for the design of new aluminium alloys for serving at elevated temperatures.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).