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A high-strength precipitation hardened cobalt-free high-entropy alloy



Matthew Luebbe, Jiaqi Duan, Fan Zhang, Jonathan Poplawsky, Hans Pommeranke, Maalavan Arivu, Andrew Hoffman, Haiming Wen


Recent studies on precipitation-hardened high-entropy alloys (HEAs) demonstrate their high strength and thermal stability, making them promising materials for high-temperature structural applications such as nuclear reactors. However, many existing HEAs contain cobalt (Co), which is unsuitable for nuclear applications because of the long-term activation issue of Co. Co is also expensive and considered a critical material for other applications. Therefore, it is desired to exclude Co from the composition. A Co-free (Fe0.3Ni0.3Mn0.3Cr0.1)88Ti4Al8 HEA was developed and studied in this work. In contrast to previous Co-free HEAs, this alloy is close to equiatomic in its composition and promises a more pronounced high-entropy effect. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and synchrotron-based, high-energy X-ray diffraction were used to characterize this alloy and revealed a complex four-phase structure with an FCC matrix, γ′ precipitates, and a network of B2 and χ phase particles. This structure granted 2151 MPa compressive strength and good thermal stability, but with limited ductility and slow precipitation kinetics. A strengthening analysis of the alloy shows that the small γ′ precipitates provided the most significant strengthening contribution (1244 GPa). The strengthening effect from the B2 and χ networks is also considerable, adding 312 MPa and 788 MPa for B2 and χ, respectively. This study lays the foundation for the continued development of high-strength Co-free HEAs with improved and satisfactory ductility.
Materials Science and Engineering A


alloy development, high entropy alloy, heat treatment, microstructure, mechanical properties


Luebbe, M. , Duan, J. , Zhang, F. , Poplawsky, J. , Pommeranke, H. , Arivu, M. , Hoffman, A. and Wen, H. (2023), A high-strength precipitation hardened cobalt-free high-entropy alloy, Materials Science and Engineering A, [online],, (Accessed June 24, 2024)


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Created April 12, 2023, Updated March 2, 2023