Influence of Loading Manner on Fatigue and Dwell-fatigue Behaviour of Ti6242

Conventional low-cycle fatigue (LCF) and low-cycle dwell-fatigue (LCDF) tests were performed at room temperature for Ti6242 alloy with bimodal microstructure. The influence of loading manner on the fatigue life, strain accumulation and failure modes of the alloy were determined under both LCF and LCDF conditions. With increasing peak applied stress, reduction in fatigue life occurred for both types of loading, accompanied by increase in accumulated plastic strain at failure. Compared with LCF, the fatigue life of LCDF decreased more significantly with increasing stress. The differences in fracture mode for both loading was identified by observing the fracture surfaces and the longitudinal section near the fracture. In the stress range investigated, LCF fracture always showed typical fatigue features including fatigue crack initiation, slow propagation and final fracture, but LCDF fracture occurred differently. When the loading stress exceeded the yield stress, the fracture of LCDF changed from the typical fatigue fracture to that similar to room temperature tensile fracture, with an obvious necking. Meanwhile, the breaking strain of the LCDF specimen above the yield stress was very large compared with LCF, close to the elongation at rupture for room temperature tensile test. The morphology of cracks in the longitudinal section also reflected the effects of loading manner on the strain accumulation and fatigue failure mode.