Surface modification processes by hypervelocity plasma pulses

Abstract The Institute of Astronautics of the Technische Universitat Munchen works in the field of electrothermal and electromagnetic particle launchers. Capacitor-driven arc discharges generated within these accelerators eject very fast and dense plasma pulses that can be used to modify surfaces of metals and alloys. During the last years, a completely new facility for surface modification purposes was designed, built, and put into operation. In preparation for the industrial application of the plasma-pulse-technique, further modifications and optimizations of the facility were performed. Fast and reliable feeding of seeding and/or reaction products to the plasma was realized with a specially designed and built gas injection system. Very short opening times for the injection valves could be realized. It is now possible to supply a substantial amount of gas to the process. The pressure pulse from the gas injection allows uniformly and finely distributed feeding of pulverized additives to the plasma as well. For the first time, we generated a carbon–nickel plasma that was used for steel-hardening. In contrast to our former experiments, a hard surface but largely free of fissures could be generated. This is a necessary and important step towards an industrial application of the plasma-pulse-technique. A different application is the surface doping of titanium aluminides (TiAl) with chlorine atoms. This modification leads to a substantial reduction of the oxidation of such materials. This is essential for the high temperature regime of turbine blades in jet engines. After the modification of the gas injection system for chlorine, TiAl samples were impacted with chlorine doped plasma pulses and the oxidation was tested. A reduced oxidation was observed which proves the principle applicability of the plasma pulse process for this special application.