Fatigue fracture behavior of a Ti17 joint under various heat treatment specifications prepared by linear friction welding

A comprehensive study to investigate and characterize the fatigue fracture behavior of linear friction welded Ti17 joint and Ti17 joint under various post welding heat treatment (PWHT) specifications is critical to providing a foundation for the life design of a 'blisk' manufactured by linear friction welding. This study addressed this issue. High cycle fatigue tests were carried out. EBSD was employed to examine the microstructures in welding center zone (WCZ), thermal mechanical affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) across the Ti17 friction welded interface. The results show that the as welded Ti17 joint tends to fracture at WCZ &TMAZ during the fatigue service with a life of 45201, where a heterogeneous structure is formed as 'refined equiaxed beta grain -coarse beta grain -basket-weave beta grain with lamellar alpha partially dissolved -basket-weave beta grain' corresponding to 'WCZ -TMAZ -HAZ -BM'. After aging at 550 degrees C, the Ti17 joint tends to fracture along the boundary between TMAZ and HAZ + BM with a life of 42338, where a heterogeneous structure is formed as 'alpha ' colony with coarse 'alpha laths' -basket-weave beta grain' corresponding to 'WCZ &TMAZ -HAZ & BM'. After aging at 630 degrees C, Ti17 joint tends to fracture at BM with a life of 75121, where a heterogeneous structure as 'refined alpha ' laths with basket-weave characteristics -coarse basket-weave of alpha ' laths in beta grains' corresponding to 'WCZ &TMAZ-HAZ & BM' region is formed.