Improving the plasticity and strength of Fe–Nb–B ultrafine eutectic composite

• We examine the micro-to-nano-scale deformation mechanism of bimodal eutectic composite.
• Microstructural features play a crucial role in improving the mechanical properties.
• Deformation induced motion and migration release effectively the excessive strain.
• Surface topography analysis elucidates the underlying deformation mechanisms.

In the present study, the microstructural evolution and improving the mechanical properties have been achieved in Fe–Nb binary eutectic alloy via controlling the amount of boron (B) content. The addition of B leads to evolution of a unique microstructure with different length-scale heterogeneities, i.e., formation of bimodal structure, spherical colonies containing length-scale heterogeneity and precipitation of primary NbFeB phase. Following the evolution of microstructure, the mechanical properties including yield strength and plastic strain were significantly enhanced from 1100 MPa to 1660 MPa and from ∼4% to ∼20%, respectively. To elucidate deformation mechanism fracture topography and lateral surface morphology analyses are performed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). From these observations two distinct plastic deformation mechanisms can be suggested by following ways: (1) deformation-induced rotation motion of dendrites/eutectic colonies and (2) deformation-induced interface migration of lamellar structure.

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