Influence of Material Property on Thickness of Modified Layer Generated by Large-area Electron Beam

In large-area electron beam (EB) irradiation method developed recently, high energy density of EB can be obtained without focusing the beam. Therefore, the wide area of material surface can be melted instantly, and high efficient surface finishing is possible. Moreover, surface functions such as corrosion resistance and water repellency of the metal molds were improved by the large-area EB irradiation, since thin resolidified layer was formed on the metal surface. It is expected that thick modified layer is effective to maintain their surface functions for long-term. Therefore, control and prediction of the modified layer thickness are important in order to obtain appropriate modified layer thickness on metals with different material properties. In this study, variations of modified layer thickness on metals with different material property are experimentally investigated. Furthermore, electron behavior during large-area EB irradiation is simulated by using an electron track analysis, and prediction of the modified layer thickness is tried with temperature distributions by using an unsteady heat conduction analysis. Experimental results show that the modified layer thickness increases with increasing energy density. The thickness with high relative permeability is larger than that with low one. Analytical results of the modified layer thickness in unsteady heat conduction analysis show quantitative agreement with experimental ones. Furthermore, the modified layer thickness on the metals with different thermal property and density is also discussed. Then, the modified layer thickness of metals with different material property can be predicted by using our unsteady heat conduction analysis model.