Strength and fatigue strength of a similar Ti-6Al-2Sn-4Zr-2Mo-0.1Si linear friction welded joint

Strengths for monotonic and cyclic loadings of similar overmatching Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti6242) linear friction welds (LFW) were studied and compared with the parent material (PM) behaviour. Non-destructive synchrotron observations revealed the presence of pores in the weld interface. The weld centre zone (WCZ) showed a higher strength leading to lower macroscopic ductility of the cross-weld samples. Local strain and normalized strain rate have been assessed by stereo digital image correlation (DIC) and revealed an early plastic activity at yielding in the vicinity of the WCZ attributed to residual stresses. For the target life, the fatigue strength was slightly reduced but compromised by a strong scatter. Indeed, an internal fish-eye fatigue crack initiation was found on an unexpected dendritic defect that was very different from the PM microstructure and the known martensitic alpha ' in the WCZ. The dendritic defect was linked to surface contamination prior to welding and led to melting.