Ultrafast microstructure modification by pulsed electron beam to enhance surface performance

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 E s (15 J/cm 2 ) treatment, there is around 30–35 μm melting layer and the new second phase with complex elemental composition (Mn 4.6 Fe 0.4 Si 3 ) in the surface modification layer. Thermal stress within different E s has a different effect on the second phase and dislocations, and the thermal stress in high E s 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 E s is up to 15 J/cm 2 , 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/cm 2 have the highest and the lowest values, respectively. • Irradiation less than 10 J/cm 2 generates “ heating mode”, while at irradiation greater than 15 J/cm 2 , “melting mode” happens. • Metastable precipitates have formed due to the dissolution of submicron-sized inclusions under melting mode. • Along with the E s increasing, it leads to the increase of stress on the irradiated layer. • The decreasing friction coefficient and increasing the nano-hardness is associated with the rising E s .