Fatigue Characteristic of Linear Friction Welded Ti-6Al-4V Joints

Abstract

A Blisk is the integrated part of rotating blades and a disk, which is recently being adopted for fan and compressor modules of jet engines for the purpose of the weight reduction and the performance improvement. The blisk is generally manufactured by milling from the large forged material. Therefore large amount of material is wasted as cutting chips. Linear friction welding (LFW) is expected to save the wasted material, which is a kind of the solid state joining. The purpose of this study was to investigate the reduction of the fatigue strength due to LFW process. The fatigue test specimens of LFW joints and the base material were made from the same forged material to minimize the effect of scatter. Fatigue tests and analysis of covariance were conducted, and it was made clear that the fatigue strength of as-welded joint was slightly lower than that of base material, and that that of post weld heat treated (PWHTed) LFW joint was the same as that of base material. Since it was thought that the fatigue strength reduction of as-welded LFW joint was due to the effect of residual stress, the residual stress was measured before and after PWHT by Center Hole Drilling method. It was confirmed that the residual stress of as-welded LFW joint remained approximately 3 mm from the weld line where the fracture occurred in the fatigue tests, and that the residual stress of PWHTed LFW joint was reduced drastically. As a conclusion, it was made clear that the fatigue strength of PWHTed LFW joint was equivalent to that of base material with the statistical data.