On the Formation of Eutectics in Variations of the Al 10 Co 25 Cr 8 Fe 15 Ni 36 Ti 6 Compositionally Complex Alloy
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INTRODUCTION
AFTER two decades of research on high entropy alloys (HEA) and compositionally complex alloys (CCA), several procedures have been cornered as being essential for a good understanding of the material inherent properties. One of the most important ones in cast alloys is probably the adequate homogenization of the alloy.[1] Removing the compositional variances that are induced by the type of casting and parameters such as cast size, cooling rate, contact to the crucible and many others allows for a reproducibility of the material by other research groups and for pushing the alloy closer to the, alas, hardly reachable thermodynamic equilibrium. This procedure has been used for centuries
A.M. MANZONI is with the Bundesanstalt fu¨r Materialforschung und -pru¨fung, Unter den Eichen 87, 12203 Berlin, Germany and also with the Helmholtz-Zentrum Berlin fu¨r Materialien und Energie GmbH, HahnMeitner-Platz 1, 14109 Berlin, Germany. Contact e-mail: anna_ [email protected] F. DUBOIS, C. VON SCHLIPPENBACH, and D.M. TO¨BBENS are with the Helmholtz-Zentrum Berlin fu¨r Materialien und Energie GmbH; M.S. MOUSA is with the Department of Physics, Mu’tah University, Al-Karak 61710, Jordan. Y. YESILCICEK and R. HESSE are with the Bundesanstalt fu¨r Materialforschung und -pru¨fung; E. ZAISER is with the Helmholtz-Zentrum Berlin fu¨r Materialien und Energie GmbH and also with the Technical University Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany. S. HAAS and U. GLATZEL are with the Metals and Alloys, University Bayreuth, Prof.-Ru¨diger-Bormann-Str. 1, 95447 Bayreuth, Germany. Manuscript submitted July 3, 2020; accepted October 29, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
in all types of alloys and is just as valid in single-phase HEA and multi-phase CCA, which add a challenge to the finding of the correct homogenization parameters by their high number of elements. During the last few years, the authors’ group has found the Al10Co25Cr8Fe15Ni36Ti6 CCA to be of high interest for a potential application at around 700 C.[2–5] Optimizing parameters have been predicted by ThermoCalc[6] using the TTNI7 database,[7] tested in numerous casting and heat treatment experiments until the best parameters had been found to be 1220 C 20 hours for homogenization. Once the alloy reached its best microstructural and mechanical properties, another path for further improvement was chosen, i.e. by the addition of trace elements that would push the properties beyond the base alloy’s. Besides the expected change in mechanical properties, a change in optimizing parameters was expected as well. It was quickly found that the homogenization temperature of 1220 C, which was used for the base alloy, was not adequate for many alloy variations because of a eutectic formation of two or three phases, subsequently called the eutectic or the eutectic phases for simplicity, both at the grain boundaries and inside the grains. Unlike in alloys designed for consisting entirely of eutectic phases,[8] which can provide good combinations of strength a
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