# Development of an Alternative Alloying Concept for Additive Manufacturing Using PVD Coating
## 3 Results
### Influence on the Arc
The conductivity of the outer layer is of relevance in the contact point of the current contact tube, since with constant power in the system and a variable electrical conductivity, the voltage dropping in the contact resistance varies and, accordingly, the voltage in the arc is changed relatively. The measurement of the resistance is measured by means of a test rig that determines the resistance at electrode caps for spot welding. For this purpose, the wire is positioned between the two electrode caps and pressed together with a test force of 100 N. The resistance of the wire is then measured. The resistance of the wire is then determined in the current contact tube. There are no contact forces in a current contact tube, but the test force is set at 100 N to reduce the measurement inaccuracy when determining the resistance. In the theory of variable electrical conductivity in the current contact tube, an aluminium oxide layer must be assumed on the weld filler coated with aluminium, which considerably reduces the conductivity of aluminium. However, this behaviour could not be proven after measurements of the conductivity of the individual layers. However, a force of 100 N was applied to the wire to obtain a higher accuracy for the measurement. Under certain circumstances, this force may have been sufficient to break up the oxide layer. However, it is noticeable in the set-up of a welding device that the wire in the wire conveyor unit is subject to similar forces, which break up a possible oxide layer, analogous to the test set-up. From the investigations, an influence on the ionisation in the arc results. According to [PERSON] (1977), the element with the lowest ionisation energy decisively takes over the ionisation state in an arc. Even traces of metal vapour have a major influence. The ionisation state refers to the electrical conductivity and the temperature in the arc. The ionisation energies of aluminium and titanium have a lower necessary energy than iron in the different ionisation states. Figure 6 shows the arc temperature plotted against the ionisation potential. The line in the diagram includes the theoretically calculated values and the crosses represent the experimentally determined values for a MIG process. It can be seen that aluminium and titanium each have a lower ionisation potential than iron. A lower ionisation potential means a higher ionisation of the gas, which in turn causes an increase in ions and electrons in the arc. A higher number of electrons means that more current can be transported. As a result, the conductivity of the arc increases and the voltage does not increase with a longer arc length. Furthermore, due to the lower ionisation potential, less energy is needed to obtain more electrons in the arc. This energy is then, in turn, available to the arc to keep the extension stable. In this study, aluminium is the element with the lowest ionisation potential but does not have the longest arc length. The diagram in Figure 6 shows that aluminium lowers the temperature in the arc. A reduction in the arc temperature results in a reduction in the electrons available in the arc, as thermal ionisation accounts for a large proportion of the ionisation in the arc. Furthermore, aluminium has a lower ionisation potential only in the first ionisation stage. The further ionisation stages require a higher energy input than is the case with titanium. It can be deduced that aluminium has a longer arc length compared to the base wire, as the ionisation energy of aluminium is lower. Furthermore, it can be deduced that titanium, however, has the longest arc length because titanium, in contrast to aluminium, does not reduce the arc temperature. The investigations have shown that the arc length varies depending on the ionisation energy and the change in temperature of the arc plasma. The lower the ionisation energy, the higher the electrical conductivity in the arc, which increases the arc length.