Plasma Diagnostic of a Plasma Immersion Ion Implantation Process for protecting TiAl Alloys against High Temperature Oxidation using Chlorine

Plasma immersion ion implantation (PIII) from a chlorine containing plasma has been used in order to improve the high temperature oxidation behavior of titanium aluminide alloys. This process is promising since the subsurface Cl concentration, which is needed for optimum protection against oxidation, can be quickly obtained (approx. fluence 1·1016 Cl/cm-2) in a PIII process.
A PIII system being resistant against the strongly etching Cl2 plasma is presented. Plasma diagnostics of the Cl2 plasma sustained by an ICP source using Langmuir probe measurements is discussed. For the electro-negative Cl plasma, the measurements are examined regarding the influence of negative ions. The implantation of Cl is correlated to the plasma parameters using AES depth profiling of the surface after implantation. The high temperature oxidation behavior is tested using thermogravimetrical analysis (TGA) in air at 900 °C and microstructural investigations of the oxide scale. PIII implantations of Cl2 with 30 kV HV pulses (effective energy 15 keV) show a strong reduction of the oxidation at 900 °C in air, which is comparable to conventional beam line im-plantations of Cl at 15 keV.