The formation mechanism of eutectic microstructures in NiAl-Cr composites

• Published in: Physical chemistry chemical physics : PCCP Vol. 18; no. 29; pp. 19773 - 19786
• Main Authors: Tang, Bin, Cogswell, Daniel A, Xu, Guanglong, Milenkovic, Srdjan, Cui, Yuwen
• Format: Journal Article
• Language: English
• Published: England 20.07.2016
• Subjects: Body centered cubic lattice; Eutectic composition; Eutectic temperature; Intermetallics; Microstructure; Nickel aluminides; Nickel base alloys; Nickel compounds
• ISSN: 1463-9076; 1463-9084; 1463-9084
• DOI: 10.1039/c6cp01921h

NiAl-based eutectic alloys, consisting of an ordered bcc matrix (B2) and disordered bcc fibers (A2), have been a subject of intensive efforts aimed at tailoring the properties of many of the currently used nickel-based superalloys. A thermodynamic phase field model was developed on a thermodynamic foundation and fully integrated with a thermo-kinetic database of the Ni-Al-Cr ternary system to elucidate the resulting peculiar eutectic microstructure. Invoking a variation of the liquid/solid interfacial thickness with temperature, we simulated the characteristic sunflower-like eutectic microstructures in the NiAl-Cr composites, consistent with experimental observations. The mechanism that governs the formation of the peculiar eutectic morphology was envisioned from the modeled evolutions associated with six sequential steps. Our calculations show that the conditional spinodal decomposition occurring in sequence could further trim and revise the microstructure of the eutectics by generating fine-domain structures, thereby providing an additional method to explore the novel NiAl-based eutectic composites with tunable properties at elevated temperatures. Based on a thermodynamic foundation, a phase field model is developed for describing eutectic composites. The inherent complexity of NiAl-Cr microstructure is rationalized by modeling eutectic solidification that precedes conditional spinodal decomposition.