  Intermetallic compounds possess unique atomic arrangements that often lead to
exceptional material properties, but their extreme brittleness usually causes
fracture at a limited strain of less than 1% and prevents their practical use.
Therefore, it is critical for them to exhibit either plasticity or some form of
structural transition to absorb and release a sufficient amount of mechanical
energy before failure occurs. This study reports that the ThCr2Si2-structured
intermetallic compound (CaFe2As2) and a hybrid of its structure (CaKFe4As4)
with 2 {\mu}m in diameter and 6 {\mu}m in height can exhibit superelasticity
with strain up to 17% through a reversible, deformation-induced, lattice
collapse, leading to a modulus of resilience orders of magnitude higher than
that of most engineering materials. Such superelasticity also can enable strain
engineering, which refers to the modification of material properties through
elastic strain. Density Functional Theory calculations and cryogenic
nanomechanical tests predict that superconductivity in CaKFe4As4 could be
turned on/off through the superelasticity process, before fracture occurs, even
under uniaxial compression, which is the favorable switching loading mode in
most engineering applications. Our results suggest that other members with the
same crystal structure (more than 2500 intermetallic compounds), and
substitution series based on them should be examined for the possibility of
manifesting similar superelastic and strain-engineerable functional properties.
