SURFACE INTEGRITY AND FATIGUE LIFE OF TURNED GAMMA-TITANIUM ALUMINIDE

This paper outlines the effect of single-point turning on the surface integrity and fatigue life of a gamma XD(TM) titanium aluminide (Ti-45 Al-2Nb-2Mn-0.8% TiB2) produced by Howmet, USA. Intermetallic materials of this type are currently been evaluated by leading aerospace compan ies world-wide for use in aeroengine applications (e.g. compressor bla des), due to their good high-temperature properties and low density (a pproximate to 50% of Ni-based superalloys). Workpiece surface integrit y defects were found after machining, including deformed lammellae/sur face drag, material pull-out/cracking (<20 mu m depth) and increased m icrohardness. Such problems were encountered in all specimens even whe n machining under fine-finishing conditions. The S-N fatigue curves, p roduced from rotating bending tests at room temperature, were 'flat' a nd contained a large amount of spread. The difference between turned a nd polished specimens was minimal, both having an endurance limit of a pproximately 350 MPa. (C) 1997 Elsevier Science S.A.