Heterostructural nanolamellar oxide-dispersion-strengthened ferritic alloy with exceptional strength and ductility

Abstract

Nanostructured ferritic alloys (NFAs) have demonstrated exceptional mechanical properties (strength and creep resistance) and radiation tolerance. However, the high strength (typically above 1.5 GPa) always comes with a significantly limited ductility. Here, we report a novel heterostructural nanolamellar ferritic alloy (NLFA) with microcrystalline (MC) domains (∼ 35 % of volume fraction) dispersed in an ultrafine-grained (UFG) matrix (∼ 500 nm grain size), enabling the alloy to achieve ultrahigh yield strength of 2 GPa and an excellent tensile elongation of ∼ 13 %. The nanolamellar-shaped grains remarkably strengthen the alloy via grain-boundary strengthening. The soft MC domains can effectively suppress the microcrack initiation and propagation along the oxide-rich preliminary powder boundaries (PPBs) via local plastic deformation. Moreover, linear oxide bands can induce numerous interlayer cracking and trigger delamination toughening, collaboratively ensuring the alloy a large ductility. The present study opens a new frontier toward high tensile ductility for the most cutting-edge ultra-strong NFAs.