Combining Strength and Ductility in a Precipitation (Γ’) Hardened Fe-Rich Compositionally Complex Alloy Via Recystallisation

Abstract

Fe-rich alloys are the most attractive among the compositionally complex alloys (CCAs) owing to the excellent combinations of mechanical properties combined with low cost. The kinetics of recrystallisation and grain growth of an austenitic Fe-35.5Ni-4Cr-6.3Al-3.2Ti alloy is systematically studied to balance the combination of high strength and good ductility through grain refinement and the precipitation of L12 (γ’) phase. The yield strength of the Fe-35.5Ni-4Cr-6.3Al-3.2Ti alloy can be tuned by thermo-mechanical processing from 294 MPa in the coarse-grained FCC (γ) phase structure to 1142 MPa through inducing a heterogeneous grain structure consisting of fine recrystallised grains, subgrains/deformed grains and precipitates. The fully recrystallised alloy showed a balanced combination of strength (~1.35 GPa) and uniform elongation (~24%). The alloy showed good strengthening by grain refinement (Hall-Petch coefficient of 581 MPa.µm0.5) and displayed an activation energy of 385 kJ/mol for static recrystallisation. The present Fe-rich CCA exhibited similar mechanical properties offered by Ni and Co-rich CCA compositions with a γ+γ’-phase structure, but at a substantially low alloying cost (< 50%).

Keywords: Compositionally complex alloys, Static recrystallisation, Precipitation strengthening, Hall-Petch strengthening, Mechanical properties