Design of ultrafine eutectic-dendrite composites with enhanced mechanical properties in Fe-based alloy

The effect of Mn content on the evolution of microstructure and the enhancement of mechanical properties in Fe-Nb-Mn hierarchical composites consisted of ultrafine eutectic and primary dendrite has been studied by using X-ray diffractometry, scanning electron microscopy, transmission electron microcopy and compression test. Fe-11Nb-5Mn hierarchical composite consisted of α′-Fe dendrite and urtrafine α′-Fe + Fe2Nb eutectic, and exhibited a reasonably good combination of mechanical properties, i.e. yield strength of 1283 ± 10 MPa and compressive plastic strain of 7.75 ± 5%, while Fe-11Nb-15Mn composite consisted of ɛ-Fe dendrite and ɛ-Fe + Fe2Nb eutectic structure with some retained γ phase, and exhibited a far better combination of mechanical properties, i.e. higher yield strength of 1462 ± 10 MPa and larger compressive plastic strain of 11.28 ± 2%. The origin for the simultaneous enhancement of high strength and large plastic strain is attributed to ɛ-Fe martensite formation and strain-induced martensitic transformation from ɛ to α′ during deformation.