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-45Al-2Nb-2Mn-0.8% TiB2) produced by Howmet, USA. Intermetallic materials of this type are currently been evaluated by leading aerospace companies world-wide for use in aeroengine applications (e.g. compressor blades), due to their good high-temperature properties and low density (approximate to 50% of Ni-based superalloys). Workpiece surface integrity defects were found after machining, including deformed lammellae/surface drag, material pull-out/cracking (<20 mu m depth) and increased microhardness. Such problems were encountered in all specimens even when machining under fine-finishing conditions. The S-N fatigue curves, produced from rotating bending tests at room temperature, were 'flat' and contained a large amount of spread. The difference between turned and polished specimens was minimal, both having an endurance limit of approximately 350 MPa. (C) 1997 Elsevier Science S.A.