Large-Area Electron Beam Melting: Frequency Analysis and Critical Frequency Prediction

During large-area electron beam irradiation, high energy flux pulses of electrons melt a thin layer of material. The objective of this work is to analyze the spatial frequencies of a turned, S7 tool steel surface before and after electron beam melting. It was observed that high frequency features are significantly reduced following melting, but lower frequency features were created and increased the unfiltered areal average roughness. Previous work on laser remelting-based polishing derived a critical frequency that defines the frequency above which higher frequency features are dampened. As the critical frequency depends on the melt duration that the surface experiences, a one-dimensional, transient temperature prediction model was created for this work to estimate the melt time for a single electron beam pulse. This model allowed for the calculation of a critical frequency that showed good ability to predict the frequencies that are dampened.