Abstract: An oxide-dispersion-strengthened (ODS) Fe-10Cr-6.1Al-0.3Zr-0.1Y alloy with a bimodal grain size distribution was developed via a simple process of internal oxidation and powder forging. The intentionally promoted heterogeneous microstructure consists of coarse-grained “core” regions enclosed by mutually connected fine-grained “shell” zones, facilitated by unevenly distributed oxide particles. The sample sintered and then forged at 1150 °C exhibited a yield strength of 598 MPa, a tensile strength of 734 MPa, and a fracture elongation of 25.1 %. Such simultaneously enhanced strength and ductility are significantly above those of cast or previous powder-consolidated counterparts. During tensile deformation, a strain gradient is built up across the inhomogeneous grains and a high density of geometrically necessary dislocations was observed near the interfaces of matrix/oxide particles, both contributing to heterogeneous deformation-induced strengthening. This elevates the work hardening rate and consequently the tensile elongation. Quantitative analysis indicates that the dislocation build-up during forging makes the dominant contribution to the high yield strength of Ox-1150. The present study offers a new route to the preparation of heterogeneously structured ODS Fe-Cr-Al alloys and provides guidance for optimizing the mechanical properties of such alloys in terms of strength-ductility synergy.

Key words: Fe-Cr-Al alloy, Powder metallurgy, Oxide particle, Heterostructure, Mechanical property