Enhanced strength-ductility combination by introducing bimodal grains structures in high-density oxide dispersion strengthened FeCrAl alloys fabricated by spark plasma sintering technology

TL;DR

This study introduces a bimodal grain structure in oxide dispersion strengthened FeCrAl alloys, fabricated via spark plasma sintering, to enhance both strength and ductility, overcoming traditional trade-offs in these materials.

Contribution

The paper presents a novel approach of combining bimodal grains with nano-oxide dispersion to improve mechanical properties of FeCrAl alloys.

Findings

Both strength and ductility are significantly improved with increased milling time.

Ultra-high-density nano-oxides are crucial for strength enhancement.

H40 alloy exhibits outstanding strength and ductility, suitable for fuel cladding.

Abstract

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.