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

• Plastic strain localisation in the grains of selective laser melted (SLM) 18Ni-300 maraging steel was characterised for the first time using scanning electron microscope-based digital image correlation (SEM-DIC). • The occurrence of slip was directly influenced by the presence of internal misorientations within individual grains. Slip preferentially occurred in grains with increased internal misorientation, and the slip bands intersected regions that exhibited increased kernel average misorientation (KAM). • Plastic deformation resulted in the simultaneous activation of 5 or more independent slip systems in selected grains, i.e. G2 from the as-built sample and G8 from the solution-aging treatment sample. • The primary slip system in G2 and G8 were identified as ( 2 ¯ 1 3 ¯ ) [ 1 ¯ 11 ] and ( 0 1 ¯ 1 ) [ 111 ] respectively (Schmid factor of 0.46 and 0.47, respectively). The combined kinematics of the active slip systems were reflected in the in-plane deformation behaviour for both grains. 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.