Results of Surface Integrity and Fatigue Study of PECM and PEO Processed γ-TiAl for Turbine Applications

Gamma Titanium aluminides (γ-TiAl) will play an important role in designing future aero engine components such as turbine blades and blisks. Due to the high heat resistance and low densities these materials are highly suitable for replacing nickel-based alloys in the high pressure compressor and low pressure turbine. Electrochemical machining (ECM) is an attractive process for manufacturing these materials because of the capability of this process to machine materials independent of their mechanical properties. Major advantages of ECM are its process specific characteristics of high material removal rates in combination with almost no tool wear. A possibility to enlarge the field of operation is a heat and corrosion protection layer made out of ceramics for the electrochemical machined turbine blades. One way to produce such a layer is the plasma electrolytic oxidation (PEO).Aero engine components are subjected to static and dynamic stresses. Component life and failure is greatly affected by aspects of the surface integrity of stressed parts, such as surface roughness values. Precise electrochemical machining (PECM) is capable of producing excellent surface integrity qualities on γ-TiAl without thermally and mechanically affecting the rim zone. In this paper the impact of different processing strategies by ECM as well as by a combination of ECM and PEO on fatigue strength with regard to component life is investigated.