From simple binary to complex multicomponent eutectic alloys

Qing Cai,Isaac Chang

doi:10.1016/j.pmatsci.2021.100779

Abstract

The eutectic solidification of almost all binary and majority of key ternary alloy systems have been studied and modelled extensively. The development of eutectic microstructure in ternary, multicomponent and high entropy alloys have generated potential engineering alloys with superior mechanical/magnetic properties that outperform their traditional binary eutectic counterparts due to refined microstructure and/or the presence of dual hard/soft phase mixture. Currently, our understanding of the eutectic solidification is mainly restricted to alloy systems having upto 3 constituents (eg. ternary eutectic). There exists a knowledge gap in our understanding of the solidification behaviour of high order multicomponent eutectic alloys. This review article gives a brief background of the development of eutectic alloys from binary to senary multicomponent systems, together with an overview of recent development of complex microstructures of aluminium based multicomponent alloys with five or more constituents at/near eutectic compositions. Although the number of crystalline phases coexisted in the Al-based eutectic alloys increases with increasing number of constituents. The solidification of a melt at near eutectic composition of 13-element alloy system has led to the development of seven crystalline phases with predominantly non-cooperative growth, leading to a microstructure free of lamellar feature, as compared to their low-order constituent alloy counterparts. Finally, the hardness of Al-based eutectic alloy increases significantly as the number of constituents in excess of ten. This opens up a new opportunity to develop ultrahigh strength alloys based on high-order multicomponent eutectic alloy systems.

Highlights

Eutectic alloys refer to a unique class of material system comprised of more than one constituent and they exhibit the lowest temperature of melting/freezing as compared to the melting point of any of the constituents
When the alloy systems become more complex and are based on a large number of constituents, our knowledge of eutectic solidification is limited and it is restricted mainly to two-phase eutectic microstructure. This is partly due to the difficulty of finding eutectic compositions in high order constituent alloy systems without any prior knowledge of co-existed eutectic phases
Our recent attempt to search for eutectic compositions in alloy systems beyond five constituents have led to the following conclusions:

Summary

Introduction

Eutectic alloys refer to a unique class of material system comprised of more than one constituent and they exhibit the lowest temperature of melting/freezing as compared to the melting point of any of the constituents. Other multiphase eutectic microstructure beyond two-phase mixture have been observed in ternary (e.g. Al-Cu-Si41,19,42, Al-Cu-Ag42,43, Al-Ni-Mg44, NbAl-Ni45,46,Al-Cu-Ni47, Fe-Mo-Si48, Fe-B-Cu49) and quaternary (e.g. Al-Cu-Si-Mg50) eutectic alloys.

Results

Conclusion