  Multi-principle element alloys have enormous potential, but their exploration
suffers from the tremendously large range of configurations. In the last decade
such alloys have been designed with a focus on random solid solutions. Here we
apply an experimentally verified, combined thermodynamic and first-principles
design strategy to reverse the traditional approach and to generate a new type
of hcp Al-Hf-Sc-Ti-Zr high entropy alloy with a hitherto unique structure. A
phase diagram analysis narrows down the large compositional space to a
well-defined set of candidates. First-principles calculations demonstrate the
energetic preference of an ordered superstructure over the competing disordered
solid solutions. The chief ingredient is the Al concentration, which can be
tuned to achieve a D019 ordering of the hexagonal lattice. The computationally
designed D019 superstructure is experimentally confirmed by transmission
electron microscopy and X-ray studies. Our scheme enables the exploration of a
new class of high entropy alloys.
