  Oxide dispersion strengthened FeCrAl alloys dispersed high-density
nano-oxides in the matrix show outstanding corrosion resistance and mechanical
properties. However, ODS FeCrAl alloys achieve the high strength generally at
the expense of ductility in some way. Here, a method by introducing a bimodal
grain structure was designed to overcome the strength-ductility tradeoff. In
this work, ODS FeCrAl alloys were successfully fabricated through various
mechanical alloying time, combined with spark plasma sintering under the vacuum
of less than 4Pa. Microstructural characterization showed that the average
grains size and nano-oxides size decrease gradually, and the density of
nano-oxides increases, as the milling time increases. Mechanical properties
revealed that both the strength and ductility were significantly synergistic
enhanced with increasing milling time. The bimodal grain distribution
characterized by electron backscatter diffraction (EBSD) (vacuum degree was
less than 5E-5pa) was beneficial for the activation of the back stress
strengthening and the annihilation of these microcracks, thus achieving the
excellent ductility (27.65%). In addition, transmission electron microscope
(TEM) characterization under the vacuum degree of less than 10-6pa illustrated
that ultra-high-density nano-oxides (9.61E22/m3) was crucial for enhancing the
strength of ODS FeCrAl alloys (993MPa). The strengthening mechanism
superposition, based on the model of nano-oxides interrelated with the
dislocation, illustrated an excellent agreement with experimental results from
yield strength strengthening mechanisms. To our best knowledge, H40 (milled for
40h, and sintered at 1100C) alloy presents the outstanding strength with the
exceptional ductility among all studied ODS FeCrAl alloys, which makes it the
promising cladding materials for the accident tolerant fuel cladding.
