Role of Microstructural Heterogeneity on Nanoscale Mechanical Properties and Wear Responses of Additively Manufactured CoCrNi Medium Entropy Alloy and 316L Stainless Steel

In the present study, a systematic comparison of additively manufactured CoCrNi medium entropy alloy having face-centered-cubic (FCC) structure with standard FCC materials 316L austenitic stainless steel was carried out. The effect of energy density (71 J/mm²) on microstructural heterogeneity and crystallographic orientation of planes parallel to the build direction (X–Z) and perpendicular to the build direction (X–Y) was recorded. Scanning electron microscopy, x-ray diffraction and electron backscattered diffraction techniques were used to reveal the surface and structural features. The effect of repetitive heating associated with layer-by-layer deposition of the X–Z axis was reflected as the favorable formation of the (1 1 1) plane at the expense of the (2 2 0) plane. The low angle grain boundaries at the X–Z axis have been decreased by ~ 27% compared to the X–Y axis for CoCrNi, while a ~ 17% reduction was recorded for 316L austenitic stainless steel. Furthermore, the decreasing trends in nanomechanical properties and wear resistance were observed, with a low number of low angle grain boundaries at the X–Z axis, by employing a nanoindenter. Significant microcracks in CoCrNi medium entropy alloy manifest the brittle fracture mode, whereas 316L alloy denotes the mixed type of failure mode.