The formation process of surface crater is affected by the different time and space distribution of the thermal flux and pressure on the cathode in the action of vacuum metal vapor arc. After taking the influence of surface tension and Marangoni into account

a transient 2 D axially symmetric melting model has been developed to describe the thermodynamic behavior of molten metal on cathode surface and the formation of a crater. Moreover

the surface structure and initial time of metal vapor injection from the crater are obtained. In the process of metal phase transition

the deformation and temperature gradient in the center of molten metal pool are remarkable. Due to the Marangoni effect and the surface tension

the energy from the center of the molten metal on the cathode surface

is transferred to the edge of the crater. At the edge of crater

the surface tension of the driving force is significant. As the temperature increases to the critical temperature

the new jet explosion point appears. The overburden layer of metal vapor density of 10

25

m

-3

on the surface of the crater is formed

in which distribution is related to the shape of the crater. By increasing the heat flux

reducing the external pressure and increasing the specified radius

the covering layer on the crater appears in advance. When the energy injected to the cathode is excessively low

the bottom of the crater is thick and the radius of the crater is small. Therefore

a dense metal vapor layer cannot be generated near the crater.