Tension and Torsion Fatigue Response of TIMETAL~R 6-4 and TIMETAL~R 550 Alloys

摘要

There are many applications in which components experience multiaxial loading conditions in service. For titanium alloys, such loading states can generate complications particularly with regard to situations in which the alloy is textured. In the present paper, a comparison is made between tension and torsion loading of TIMETAL~R6-4 rolled plate and forged TIMETAL~R550. The textures and microstructures in the two alloys are significantly different and impact on the observed mechanical response. The torsion specimens have a tubular design and were machined from the starting material at 0°, 45° and 90° to the principal deformation direction (e.g. rolling direction). The testing involved strain control loading modes at R = 0 and covered lives of 10~3 to 10~5 cycles at ambient temperature. The torsion fatigue lives display a strong dependence on specimen orientation within the rolled plate. There are also important differences between torsion and tension loading emphasising the relative significance of tensile and shear stress in the fatigue failure process. Detailed fractographic observations relate the fracture response to the orientation of the basal planes and the plane of maximum shear. Comparisons with previous torsion data on more and less heavily textured TIMETAL~R6-4 have proved to be highly informative.