Enhanced Strength–Ductility Combination by Introducing Bimodal Grains Structures in High-Density Oxide Dispersion Strengthened Fecral Alloys Fabricated by Spark Plasma Sintering

Oxide dispersion strengthened (ODS) 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 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 illustrated that ultra-high-density nano-oxides (9.61×1022/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.