  Homogeneous face-centered cubic (fcc) polycrystalline CoCrFeNi films were
deposited at room temperature on (0001)alpha-Al2O3 (c-sapphire). Phase and
morphological stability of 200 to 670 nm thick films were investigated between
973 K and 1423 K. The fcc-phase persists while the original <111> texture of
30-100 nm wide columnar grains evolves into ~10 or ~1000 micron wide grains.
Only the grains having specific orientation relationships to the sapphire grow;
as in the case of pure fcc metal (M) films 4 orientation relationships (OR) are
found: OR1 (M(111)[1-10]//alpha-Al2O3 (0001)[1-100]) and OR2
(M(111)[1-10]//alpha-Al2O3 (0001)[11-20]) and their twin-related variants (OR1t
and OR2t). Below 1000 K, the film microstructure stabilizes into 10 micron wide
OR1 and OR1t twin grains independent of film thickness. Above 1000 K, the OR2
and OR2t grains expand to sizes exceeding more than a 1000 times the film
thickness. Upon annealing, the films either retain their integrity or break-up
depending on the competing kinetics of grain growth and grain boundary
grooving. Triple junctions of the grain boundaries, the major actors in film
stability, were tracked. Thinner films and higher temperatures favor film
break-up by dewetting from the holes grooved at the triple junctions down to
the substrate. The grain boundaries of the OR2 and OR2t grains migrate fast
enough to overcome the nucleation of holes from which break-up could initiate.
The growth of the OR2 and OR2t grains in this complex alloy is faster than in
pure fcc metals at equivalent homologous annealing temperatures.
