Influence of cathode materials (Ti, Al, Cu, TiN), ambient gases (Ar, Nz, p = 0.1-1 Pa) and the arc current itself on the motion and the velocity of cathode spots in an arc coating process have been investigated with the help of a new high speed framing camera. It was found, that the cathode material causes different spot currents but in general the spot arrangement and the motion on the surface are similar. Surface contaminations due to ambient gases affect this dynamics in several ways. Insulating layers like AlN can drastically increase the instantaneous spot velocity, for example from <5 m/s on A1 up to 170 m/s on AIN contaminated areas. TIN layers with a high conductivity increase the spot mobility at first. But at nearly completely contaminated surfaces (simulated by a TIN cathode), the mobility is strongly decreased. The values change from an average velocity of 6.3 m/s with a diffusion constant of 54 cm2/s (Ti, 0.01 Pa) to 2 m/s and 6.4 cm2/s at TiN.The course of the instantaneous spot velocity during the spot splitting phase was investigated too. The instantaneous spot velocity of each of the two new spots originated from the starting spot is relatively high (30-40 m/s) within the first 50 p. The cathode material and the ambient gases are of slight influence in this phase. The movement is directed. In the further development the instantaneous spot velocity is decreasing to values under 5-10 m/s. The motion is now more and more random. Additionally it could be proved, that the lower stability limit for a stable discharge is strongly connected with the spot current, which depends on discharge conditions.
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