Heterogeneous Lamella Design to Tune the Mechanical Behaviour of a New Cost-Effective Compositionally Complicated Alloy

Abstract

A novel heterogeneous lamella (HL) design strategy was proposed to improve mechanical properties of a new cost-effective Fe 35 Ni 35 Cr 25 Mo 5 compositionally complicated alloy (CCA). A HL structure was produced by single-step heat treatment (800 °C for 1h) after cold rolling. This HL structure consists of alternative lamellae regions of coarse-grained FCC matrix (5∼20 μm), and regions containing ultra-fine grains or subgrains (200∼500 nm) together with nanoprecipitates (20-500 nm) and annealing twins. The 800 °C annealed sample with HL structure demonstrated a superior tensile property, with yield strength over 1.0 GPa and ductility of ~13%. Formation of the annealing twins and nanoprecipitates decorated HL structure was a result of the concurrent partial recrystallization and precipitation of σ phase at the shear bands with a high density of lattice defects (e.g. high-density dislocation walls and deformation twins). The latter restricted the growth of recrystallized grains, leading to the formation of ultrafine subgrains within the HL structure. The high yield strength resulted from the multistage hetero-deformation induced (HDI) strengthening and precipitation strengthening associated with heterogeneous lamella structures containing nanoprecipitates. The ductility was originated from the coexistence of multiple deformation mechanisms, which started with dislocation slip and formation of stacking faults at the initial stage, followed by nano-twinning at the higher strain level. This HL design strategy, comprising of composition and thermomechanical process designs, and the resultant microstructure tuning, open a broader window for development of cost-effective CCAs with enhanced performance.