High-entropy alloys (HEAs) present a complex and fascinating case in the realm of materials science due to their unique features, including high configurational entropy, sluggish diffusion, and potential for the formation of various solid-solution and intermetallic phases.

Many factors, such as temperature, pressure, cooling rate, and composition, influence HEAs' phase evolution. Indeed, in many cases, HEAs have been found to retain the high-temperature phase structure upon cooling to room temperature, contrary to what might be predicted by the phase diagrams. This phenomenon has often been attributed to the so-called "sluggish diffusion" effect, whereby the high configurational entropy of HEAs leads to slower atomic diffusion rates, inhibiting phase transformations during cooling.

However, as you mentioned, there is an ongoing debate about the extent and impact of the sluggish diffusion effect in HEAs. Some researchers, like Murty et. al. (2020), have challenged the idea that diffusion in HEAs is universally sluggish. They argue that the diffusion behaviour in HEAs is much more complex and can be influenced by various factors, such as the specific alloy composition and the local atomic environment.

Now, addressing your query about cases where the expected room temperature phases are achieved in HEAs, there are such instances.

Several factors can influence phase transformation in HEAs:

Although HEAs are often described as single-phase materials, the reality is that many HEAs exhibit multiphase microstructures, especially when alloying elements are added or subtracted, or when they are subjected to different processing conditions. Hence, understanding the phase behaviour in HEAs is a complex task that requires consideration of the specific alloy composition and the thermomechanical history of the material.

Joshua Depiver Thank you so much for your input(s). Please would it be possible for you to back up your composition (AlCoCrFeNi) claim with a reference? In terms of slow cooling rates, how do you compare HEA slow cooling to slow cooling in conventional alloys? How can slow cooling be achieved during vacuum arc melting to ensure the required transformation?