Ultrafast microstructure modification by pulsed electron beam to enhance surface performance

Abstract

Pulsed electron beam surface treatment was used to enhance the microstructure and surface mechanical properties. After treatments with different electron beam energy densities, the microstructure and nano-structure of additively manufactured Al-Mg alloys were evaluated by scanning and transmission electron microscopy. At high Es (15 J/cm2) treatment, there is around 30–35 μm melting layer and the new second phase with complex elemental composition (Mn4.6Fe0.4Si3) in the surface modification layer. Thermal stress within different Es has a different effect on the second phase and dislocations, and the thermal stress in high Es improves the dissolution of submicron-sized inclusions presented in the initial state to form new particles. KAM (Kernel Average Misorientation) maps and calculated values prove that the electron beam irradiation increases the degree of local misorientation and surface stress. As Es is up to 15 J/cm2, the value of KAM and stress, as well as the dislocation, is the maximum. The formation of subgrains and precipitates with complex elemental composition after irradiation has comprehensive effects on the nano-hardness, wear rate and friction coefficient. It reveals that the nano-hardness and the friction coefficient of samples irradiated by 15 J/cm2 have the highest and the lowest values, respectively.