Correlation Between Process Variables And The Coating Feature In Wire Explosion Spraying

Electrical explosion spray technology is inputting the high-voltage pulse on wire material which will explode, then the explosion products spatter to the surrounding in a high speed under the impact, which will be deposited on the matrix surface forming coating. This technology is fit for refractory metals such as tungsten, molybdenum. Especially suitable for coating the inner surface of the workpieceThe quality of the coating and the bond strength are influenced by many process variables such as the voltages of electrical field, spraying distanc, the geometries of the filamentous material, the nature of the matrix . For understanding their relation completely, a series of experiments of electrical explosion was carried out in a segmented wire explosion setup. The wire explosion coatings were obtained with variations of the voltages between electrodes, lengths of segmented wire and spraying distances. The coating features were analyzed by scanning electron microscope.With variations of the voltages of electrical field and distance between electrodes, a series of experimental explosion of segmented metal wire was carried out, then the wire explosion coatings were obtained with variations of spraying distances. Results show that, When the air gap reached about 3 - 5mm, the wire explosion coating is salient. So in a specific distance of electric field, the length of the wire can be determined reasonably. The length of the wire also have relative with the attachment area of the coating , with the reducing of the length of the wire and the distance between electrodes, the coating scope was increasing.Four different types of coating were obtained with variations of parameters such as voltages of electrical field and spraying distances, which were the molten particles coating, solid particle coating, vapor deposition coating and gas accumulated coating. In those coatings, the bonding strength of the molten particles coating and vapor deposition coating were highest which have the industrial application values. By understanding the characters of the coatings, the results show that, with the increasing of the input energy density, the amount of molten drop was decreased in the exploded production, and the vapor-phase was increased. The spraying distance is a vital process variable to determine coating feature. The vapor deposition coating can be obtained only at the short spraying distance, and the range of the spraying distance is larger for obtaining the molten particles coating. With variations of diameter of the metal wire , a series of experiment was carried out. The results show that, with increasing of the wire diameter, the volume and the quality were increasing in a square number and the energy per unit volume become very little. The particle size of the coating increased from 1μm to 5μm, the surface morphology of coating was changed from aggregates -dense- looseThe surface morphology of coating was observed by scanning electron microscopy (SEM). The character of the coating was studied from the porosity rate, bonding, particle deformation. When the energy is low, the coating formed by the molten droplets . When the energy is higher enough, the solid particle would be deposited on the substrate surface and form the coating finally. The coating is high bonding strength and low porosity. There were some defects about 1μm-2μm because of uneven stackingBy calculating the energy density of the four kinds of different coatings, the approximate range of energy density of every coatings was be confirmed. with the increasing of the inputting energy density, the amount of molten drop was decreased in the exploded production, and the vapor-phase was increased. The results also show that, the inputting energy density directly decided the size, the speed and the temperature of the particles in the explosion .The voltage and the current waveforms of the explosion was measured by double voltage dividers and self-integral rogowski coil . From the waveforms, the characters of the voltage and the current as well as the process of the explosion were studied primarily.