Microstructural evolution and hardness enhancement in a novel Cr-Mn-Fe-Co-Ni high entropy alloy processed by laser surface remelting

Besides solid solution strengthening, microstructural refinement is another approach that can enhance the mechanical strength of high entropy alloys. This can be achieved using the high cooling rates inherent to the laser surface remelting process. In this work, the surface of a novel arc-melted Cr35Mn5Fe5Co5Ni50 (%at.) alloy was modified by laser surface remelting. Two laser powers were used in this work, 200 W and 300 W, to study the influence of heat input on the resulting microstructure. A fixed laser scanning velocity of 11.6 mm/s was used. Microstructural characterization was performed using X-ray diffraction, optical microscopy, and scanning electron microscopy. Electron backscattered diffraction analysis was also used to evaluate grain size and crystallographic orientation in the remelted surfaces. The laser tracks showed significant grain size refinement in comparison to the substrate. The laser track processed with the lower laser power (200 W) had the most refined microstructure, with an average grain size of 23 mu m. The laser track processed with the higher laser power (300 W) showed an average grain size of 54 mu m. The substrate displayed an average grain size larger than 200 mu m. A significant increase in microhardness, from 160 +/- 5 HV (substrate) to 189 +/- 10 HV (200 W) and 196 +/- 4 HV (300 W), was observed in the laser track areas, which is attributed to the significant microstructural refinement obtained in the remelted areas.