Depth-dependent energy absorption control of large pulsed electron beam (LPEB) irradiations for defect-free surface modification of metallic alloys

Electron beam surface finishing offers the ability to treat various materials and shapes while enhancing surface properties such as wear and corrosion resistance. However, its industrial application is limited by the formation of crater-like defects' pulse count, irradiation angle, and energy density, were optimized to achieve defect-free surfaces. By systematically investigating the synergistic effects of previously studied parameters (irradiation angle and energy density), the optimal conditions were established through strategic combination of these parameters, demonstrating enhanced surface quality and reduced defect formation. These were compared to previously optimized conditions that focused solely on increasing pulse counts. The new conditions significantly reduced the density of crater-like defects and produced smoother surfaces. This improvement is attributed to concentrated energy absorption near the surface and the creation of a high-temperature gradient, which prevents the introduction of non-metallic inclusions. Unlike conventional methods, where accumulated heat leads to phase transformations and reduces hardness and corrosion resistance, the new approach maintains a rapid cooling rate. This allows the surface to retain a fully martensitic phase even at 45 pulses, resulting in higher surface hardness. These findings highlight that the newly developed conditions not only produce defect-free surfaces but also impart enhanced mechanical properties. This approach suggests that future improvements in surface quality for electron beam-based processes can be achieved by considering adjustments to the irradiation angle and energy density.