Low-Energy High-Current Electron Beam Surface Modification of Hard Metal Cutting Tools With Different Content of Cobalt

Low-Energy (15 - 30 kV) High-Current (up to 25 kA) Electron Beam (LEHCEB) is a vacuum based technique which relies on Electron Explosive Emission inside a Plasma-Filled Diode to produce wide-area (50 cm2) electron discharges. Depending on operating parameters, the delivered energy density ranges from 0.5 to 6 J/cm2, with a pulse duration of 2.5 μs on average and repetition frequency up to 0.2 Hz. Surface treatments by means of LEHCEB allow modifications of a thin layer (0.1 - 10μm) by melting and evaporation of the material followed by rapid solidification. The very short duration of each single EB pulse allows to generate high thermal gradients, up to 109 K/s. In general, after LEHCEB irradiation, grain refinement and formation of non-equilibrium crystalline structures are observed. Moreover, chemical composition is homogenized, and surface impurities or contaminants are removed. LEHCEB irradiation was investigated as a promising surface treatment for WC-Co10 and WC-Co20 to form a surface layer characterized by mixed WC grains and Co matrix, quenched directly from liquid phase. LEHCEB treatment allowed to produce a modified surface layer characterized by increased Vickers microhardness on WC-Co20 and by improved acidic corrosion behaviour on WC-Co10.