Rapid precipitation in an Al_0.5CrFeCoNiCu high entropy alloy

Abstract

The effect of cooling rate on the microstructural evolution of Al_0.5CrFeCoNiCu has been studied using differential scanning calorimetry and scanning electron microscopy. As cast Al_0.5CrFeCoNiCu 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 Al_0.5CrFeCoNiCu is not, as previously suggested, sluggish.

Keywords:

• High entropy alloys
• Phase transitions
• Kinetics
• Precipitation