Influence of microstructural heterogeneity on the plastic strain localisation in selective laser melted 18Ni-300 maraging steel

Abstract

Plastic strain localisation in selective laser melted (SLM) 18Ni-300 maraging steel under uniaxial tensile loading was characterised via electron backscatter diffraction (EBSD), in-situ tensile experiments, and digital image correlation under the scanning electron microscope (a methodology known as SEM-DIC). Two sample conditions were investigated, namely the as-built (AB) and solution-aging treatment (SAT) conditions. During plastic deformation, the large quantity of equiaxed grains in the AB sample led to grain boundary strengthening, while the presence of densely distributed Ni-based intermetallics in the SAT sample led to strain hardening. SEM-DIC analysis revealed that plastic strain localisation in AB and SAT samples exhibited significant heterogeneity and was highly localised. Slip was identified as the main deformation mechanism for both AB and SAT samples, and preferentially occurred in grains with increased internal misorientation. Five or more independent slip systems were active in the investigated grains of AB and SAT samples during plastic deformation. The combined kinematics of the active slip systems were reflected in the in-plane deformation behaviour for the investigated grains (i.e. G2 in AB sample and G8 in SAT sample). The findings of the present work would provide fundamental insights into tailoring the material’s microstructure for optimised performance in industrial applications.