**4. General conclusion**

The failure of coating during processing was observed for the entire range of pulse parameters that were employed. In order to save already deposited layer, it is necessary to limit the processing time by the beginning of its failure.

As mentioned previously, when chemical composition of the substrate surface becomes as same as that of treating electrode after some deposition, the mass transfer from treating electrode to substrate ceases down. This is a limitation on coating thickness in ESA technology. Therefore, pulse energy was increased in order to increase the mass loss of treating electrode and its transfer to the substrate. However, it was experimentally found out that the other limitation of mass transfer, in turn limitation on layer thickness is the destruction of already deposited layer during processing. This was due to local evaporation of materials underneath the outer surface of deposit. Evaporation was due to the heat provided locally by spark discharges of high energy pulses.

Most of the molten material at the tip of the treating electrode could not be ejected out. Part of the ejected molten mass could be transferred to substrate and the rest is wasted. The ejected mass, so the transferred mass, could be increased by the employment of pulse groups instead of employing individual pulses (Rybalko et al., 1998; Ribalko et al., 2006, 2008). Mass transferred to the substrate could also be increased by the choice of an optimum scanning rate of the treating electrode. Because cross-section of a single deposit has very big difference in thickness (if the mass transfer time is long), the spot has higher thickness in center. For a continuous coating, the subsequent spot should partially overlap with previous spot. But, continuity of coating essentially depends on the experience of the operator. Thus, a continuous coating with uniform thickness demands compulsory automated spot deposition system with pre-determined rate of speed to provide necessary level of spot overlapping. Consequently, the non uniformity in coating thickness could be lowered and average coating thickness, that is mass transfer, would essentially be increased.
