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

Abstract

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 β grain - coarse β grain - basket-weave β grain with lamellar α partially dissolved - basket-weave β grain’ corresponding to ‘WCZ - TMAZ - HAZ - BM’. After aging at 550 °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 ‘α′ colony with coarse ‘α laths’ - basket-weave β grain’ corresponding to ‘WCZ &TMAZ - HAZ & BM’. After aging at 630 °C, Ti17 joint tends to fracture at BM with a life of 75121, where a heterogeneous structure as ‘refined α′ laths with basket-weave characteristics - coarse basket-weave of α′ laths in β grains' corresponding to ‘WCZ &TMAZ -HAZ & BM’ region is formed.