Abstract
Bulk metallic glasses (BMGs) and nanocrystalline metals (NMs) have been extensively investigated due to their superior strengths and elastic limits. Despite these excellent mechanical properties, low ductility at room temperature and poor microstructural stability at elevated temperatures often limit their practical applications. Thus, there is a need for a metallic material system that can overcome these performance limits of BMGs and NMs. Here, we present novel Cu-based metal-intermetallic nanostructured composites (MINCs), which exhibit high ultimate compressive strengths (over 2 GPa), high compressive failure strain (over 20%), and superior microstructural stability even at temperatures above the glass transition temperature of Cu-based BMGs. Rapid solidification produces a unique ultra-fine microstructure that contains a large volume fraction of Cu5Zr superlattice intermetallic compound; this contributes to the high strength and superior thermal stability. Mechanical and microstructural characterizations reveal that substantial accumulation of phase boundary sliding at metal/intermetallic interfaces accounts for the extensive ductility observed.
Highlights
Selecting the two major alloying components, Cu-Zr compositions located at the narrow eutectic region between ductile metal (Cu) and strong intermetallic compounds were considered (The three possible phase diagrams are available in Supplementary Information)[20,21,22]
It is interesting to observe that the Cu85Zr10Ti5 system features only two phases (Fig. 1(e)): a Cu phase (Fig. 1(f)) as well as the Cu-Zr superlattice intermetallic phase (Fig. 1(g))
From high-angle annular dark-field (HAADF) analysis, we confirmed that the Cu phase is supersaturated with Ti
Summary
Selecting the two major alloying components, Cu-Zr compositions located at the narrow eutectic region between ductile metal (Cu) and strong intermetallic compounds were considered (The three possible phase diagrams are available in Supplementary Information)[20,21,22]. This narrow compositional window in the eutectic region allows us to achieve a composite having a large volume fraction (~60%) of intermetallic compounds with minimal use of Zr, an expensive secondary alloying element, according to Gibbs phase rule. The addition of a third element (Ti or Al) was chosen to further enhance the composite by influencing the production of a strong, supersaturated Cu phase or a NC intermetallic phase, respectively, which makes an additional contribution to the high strength of the MINCs23–25
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