The Different Roles of Entropy and Solubility in High Entropy Alloy Stability

Multiprincipal element high entropy
alloys stabilized as a single
alloy phase represent a new material system with promising properties,
such as high corrosion and creep resistance, sluggish diffusion, and
high temperature tensile strength. However, the mechanism of stabilization
to form single phase alloys is controversial. Early studies hypothesized
that a large entropy of mixing was responsible for stabilizing the
single phase; more recent work has proposed that the single-phase
solid solution is the result of mutual solubility of the principal
elements. Here, we demonstrate the first self-consistent study of
the relative importance of these two proposed mechanisms. In situ
high-throughput synchrotron diffraction studies were used to monitor
the stability of the single phase alloy in thin-film (Al1–x–yCuxMoy)­FeNiTiVZr composition spread
samples. Our results indicate that a metastable solid solution can
be captured via the rapid quenching typical of physical vapor deposition
processes, but upon annealing the solid-solution phase stability is
primarily governed by mutual miscibility.