In situ martensitic phase reinforced Fe–Nb–Ni–Mn ultrafine composite with enhanced mechanical properties

An in situ formed martensitic dendrite reinforced Fe–11Nb–10Ni–5Mn ultrafine composite was developed by copper mold casting. This new class of ultrafine composite composed of micrometer-scale martensitic α′-Fe dendrites and ultrafine-scale alternating eutectics exhibits a high fracture strength of 1.6 GPa and a large compressive plasticity up to 10.5%. These excellent mechanical properties originate from the precipitation of the martensitic α′-Fe dendrites containing numerous nanometer-scale laths which are effective to generate multiple shear banding and restrict the rapid propagation of localized shear bands.

► Fe–Nb–Ni–Mn alloy with martensite dendrite embedded in ultrafine eutectic composite.
► Ultrafine eutectic matrix consisting of α′-Fe and Fe2Nb phases, together retained γ-Fe.
► Strain-induced phase transformation of retained γ-Fe to α′-Fe martensite in eutectic region.