Improvement of the high temperature oxidation behavior of TiAl via Ion implantation

Introduction

g-TiAl based intermetallic compounds are very promising for structural materials in high temperature application, because of the low density of 3.6 g/cm³. The problems, which hinder the use of this material, are the low ductility at room temperature and the oxidation above 700 °C. In particular in aircraft turbines they can replace the superalloys as turbine blades, which could lower kerosene consumption substantially..

Alloying of ternary elements in order to improve the oxidation resistance usually has a negative influence on the mechanical properties. Up to now, there is no good alloy composition for ductile and high temperature resistant TiAl alloy available.

Ion implantation gives the possibility to improve both properties separately. On the other hand a quick and precise alloying of the surface is possible. Different elements were implanted (e.g. Cl, Si, Mo, B, F, J, etc.) 

 
 

Implantation of Chlorine

Most promising element to improve the oxidation resistance is Chlorine. Because the mechanism of the protection is catalytic, the needed fluence is small. A detailed investigation of the effect led to the assumption that a selective mass transport via volatile chlorides is the substantial part of the mechanism. This model was set up mainly due to thermodynamic considerations. The experimental examination is possible by systematic ion implantations and ratify the model.

 

Figure: Parameter screening of Cl- Implantations. The resulting oxidation kinetics is improved for several orders of magnitude (green) compared to unimplanted material (red). (TGA at 900°C in air, DECHEMA e.V.)     Since the results of the low energy implantations (15 keV) showed a positive result, first test implantations in a high vacuum a plasma immersion chamber with dry Cl₂ gas were performed. This implantation procedure permits a quick implantation of arbitrary formed workpieces and is thus interesting for application. Chlorine plasmas are used in the semiconductor physics for corroding structures. Application to chlorine implantation is new and promising in this field. It was shown that during the implantation complicated process take place. The implantation profile is determined mainly by the etching rate, which can be controlled by the implantation temperature. In particular it could be shown that by means of Cl implantations without influence on the material properties (no thermal load, no alloying effects on the mechanical characteristics) a long-term oxidation protection is possible.
 

Publications:

Schumacher, G., Lang, C., Schütze, M., Hornauer, U., Richter, E., Wieser, E., Möller, W.
Improvement of the Oxidation Resistance of g- Titanium Aluminides by Microalloying with Chlorine using Ion Implantation
Materials and Corrosion 50, (1999) 162-165

Hornauer, U., Richter, E., Wieser, E., Möller, W., Schumacher, G., Lang, C., Schütze, M.
Improvement of the High Temperature Oxidation Resistance of Ti50Al via Ion Implantation
Nucl. Instr. Meth. B, B 148 (1999) 858

Schumacher, Gerd; Dettenwanger, Franz; Schütze, Michael; Hornauer, Ulrich; Richter, Edgar; Wieser, Egbert; Möller, Wolfhard
Microalloying effects in the oxidation of TiAl Materials
Intermetallics Vol. 7 10 (1999) 1113-1120

Hornauer, Ulrich; Günzel, Reinhard; Reuther, Helfried; Richter, Edgar; Wieser, Egbert; Möller, Wolfhard; Schumacher, Gerd; Dettenwanger, Franz; Schütze, Michael
Protection of gamma-based TiAl against High Temperature Oxidation using Ion Implantation of chlorine
Surface and Coatings Technology (in print)

U. Hornauer, E. Richter, W. Matz, H. Reuther, A. Mücklich, E. Wieser, W. Möller, and G. Schumacher, M. Schütze
Microstructure and Oxidation Kinetics of Intermetallic TiAl after Si- and Mo- Ion-Implantation
Proceedings SMMIB 99 (accepted)