Surface Modification Study Based On The Pseudospark Electron Beam Discharge

Electron beam surface modification plays an important role in the modern industry,especially in the field of material processing.The primary characteristics of the pulse-type source is the energy compression on the time scale,which is characterized by the fast energy storage and emitting processes to obtain high power density in a nanosecond time scale.The pulsed electron beam in our work is generated by a ‘pseudospark' discharge device,which is characterized by high current(hundreds of amperes to thousands amperes),short pulse duration(hundreds of nanoseconds to thousands nanoseconds),high frequency(hundreds Hz to thousands Hz)and self-focused beam diameter(typically 0.5-5 mm).The fast pulsed electron beam is a dynamic heat source with extremely high heating rate and cooling rate,which is capable of modulating the surface modification processes for different kinds of materials.A micro-scale model based on Monte Carlo simulation is established to simulate the micro-scale particle-material interactions during the irradiation process of the electron beam on varying material layers.The simulation is based on the trajectories of numerous electrons and matter atoms in a diversity of collision and scattering processes,taking into account the element composition,workpiece density,electron beam acceleration voltage,energy distribution and other parameters.The objective of the Monte Carlo simulation is to better understand the physical mechanism and present quantitative analysis of the influences of machining parameters on the electron beam surface treatment performances.The energy distributions along the radius and beam incident directions are testified to obey Gaussian distribution.A “Double-Gaussian” thermal model based on Monte Carlo simulation is carried out.In the process of electron beam surface modification,proper electron beam parameters and beam scan path are critical to optimize the distribution of the dynamic temperature field.A hybrid particle-thermodynamic model is present in our work to simulate the temperature disctribution during the electron beam surface modification process.The simulations model can be used to predict the treatment performances and thus optimize the design of the pseudospark electron beam processing system.Based on above simulation and theoretical analysis,the experimental platform for the pulsed electron beam material processing is designed and constructed.And the experiments of the pseudospark-based electron beam metal surface modification is conducted.The results validated that the corrosion resistance can be effectively enhanced after given pseudospark electron beam treatment processes.The improvement of corrosion resistance is mainly due to a variety of effects,including the formation of austenite which is characterized of excellent corrosion resistance,the removal of the impurities during the electron beam surface treatment process and the formation of the amorphous phase which act as a homogeneous passive film.In summary,in this study,the pseudospark electron beam surface modification experimental platform is designed and constructed.A hybrid particle-thermodynamic model is developed to calculate the transient temperature distributions of the electron beam irradiated metal surface and thus to validate the performances of the metal surface topography and quality of the metal after irradiation treatment.Finally,the mechanism of improvement of surface amorphous,grain refinement and corrosion resistance are analysed and summarized.