Abstract
The effect of cooling rate on the microstructural evolution of Al0.5CrFeCoNiCu has been studied using differential scanning calorimetry and scanning electron microscopy. As cast Al0.5CrFeCoNiCu contained three phases; Cr–Fe–Co–Ni solid solution dendrites, Cu rich interdendritic material and L12 precipitates. During cooling at rates between 10 and 50°C min−1, an additional exothermic event, at ∼1010°C, was observed in the heat flow curves. Microstructural examination after cooling revealed the presence of two distinct populations of intragranular precipitates not present in the as cast material. Energy dispersive X-ray spectroscopy indicated that Cu rich precipitates formed within the dendrites, while a Cr–Fe–Co rich phase formed in the interdendritic constituent. Precipitation during cooling at rates approaching 1°C s−1 indicates that the diffusion kinetics of Al0.5CrFeCoNiCu is not, as previously suggested, sluggish.
Highlights
Multiprincipal element high entropy alloys (HEAs), where each of the major constituents has a concentration between 5 and 35 at-%,1 offer a new approach in materials development with practically limitless potential combinations
Ng et al.[15] suggested that the diffusion kinetics of this alloy were sufficiently slow that no microstructural evolution occurred when furnace cooled from elevated heat treatment temperatures
The sigmoidal deviation has been associated with the dissolution of the L12 precipitates back into solution, while the two large endothermic peaks correspond to the melting of the interdendritic material and the dendrites respectively.[16,17]
Summary
Multiprincipal element high entropy alloys (HEAs), where each of the major constituents has a concentration between 5 and 35 at-%,1 offer a new approach in materials development with practically limitless potential combinations. It was suggested that this high entropy of mixing extended the mutual solubility of different elemental species, stabilising simple structured solid solutions with respect to the formation of intermetallic compounds.[1] Studies of alloys of this type have identified a number of promising properties, including high strength,[1,2,3,4,5] good wear characteristics[6,7,8,9,10] and excellent corrosion resistance.[11,12,13] while over 1400 scientific manuscripts have been published in this area to date, much of the underlying science of these materials remains under debate. It was proposed that the timescales required to enable a phase transformation were such that the slow cooling rates employed were equivalent to quenching a conventional alloy
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