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On the high-temperature stability of the Al8Cu3Ce intermetallic in an additively manufactured Al-Cu-Ce-Zr alloy...

by Felix Theska, Ying Yang, Kevin D Sisco, Alexander J Plotkowski, Sophie Primig
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Materials Characterization
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High-temperature resistant eutectic Al alloys are crucial materials for lightweight and energy efficient design in the automotive and aviation industries. Additive manufacturing offers a pathway to refine eutectic microstructures and develop novel alloys with superior high-temperature strength. High-volume fraction intermetallic Al-Cu-Ce alloys have been developed to deliver high-temperature strength in combination with reduced hot-tearing susceptibility. Zr is added to provide additional strengthening via nanoscale Al3Zr precipitation, and to stabilize and avoid coarsening of the Al8Cu3Ce phase. However, the detailed interaction between Zr and Al8Cu3Ce remains unexplored. In this work, we show with synchrotron X-ray diffraction that laser powder bed fusion fabricated Al-Cu-Ce and Al-Cu-Ce-Zr alloys contain predominantly the Al8Cu3Ce intermetallic in the as-fabricated condition. Heat treatment of the Al-Cu-Ce alloy results in the Al8Cu3Ce → Al8Cu4Ce phase transformation. In the Al-Cu-Ce-Zr alloy, minor fractions of (Al,Cu,Si)4Ce and Al2Cu-θ are found in the as-fabricated condition, while Al8Cu3Ce remains stable during heat treatment. Atom probe microscopy quantifies intermetallic stoichiometries and reveals how Zr is enriched at the Al-matrix/Al8Cu3Ce interface acting as a diffusion barrier against solute exchange. Calibrated thermodynamic modeling underpins this as a kinetic effect. A qualitative microstructural model summarizes, how Zr stabilizes Al8Cu3Ce against phase transformations and coarsening.