Macro and micro structural responses of dissimilar TC4/TC17 titanium alloy joints in linear friction welding and post-welding heat treatment processes and their effects on tensile and fatigue performance

The heterogeneous TC4 (Ti-6Al-4V) / TC17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) joint, formed by linear friction welding (LFW) and post-weld treatment, shows significant potential for blisk manufacturing in aircraft engines. Both LFW and heat treatment involve numerous parameters that can substantially impact joint performance, including strength and fatigue. Macroscopically, welding parameters affect the interface micro voids, influencing tensile strength, while microscopically, post-weld aging can alter the interface microstructure and affect fatigue performance. However, optimizing LFW and post-weld heat treatment for dissimilar titanium alloys remains underexplored. This study investigates the macro and microstructural responses of TC4/TC17 joints during LFW and post-weld aging, focusing on tensile and fatigue properties. Welding was performed at varying pressure (30-150 MPa) and frictional speed (240-400 mm/s) to evaluate burn-off length, interface integrity, and tensile strength. Aging treatments (550-680°C, 4h) were applied to examine their effects on microstructure and fatigue. Results show that a sufficient burn-off length is crucial for joint performance, with welding parameters affecting interface quality, such as micro-voids, which influence tensile strength. The optimal welding conditions for TC4/TC17 joints were found to be 120 MPa pressure and 288-400 mm/s frictional speed, producing defect-free interfaces with joint efficiency comparable to the base material. Aging between 630°C and 680°C caused minimal changes to microstructure and fatigue life, with cracks initiating in the TC4 base material. These insights help optimize LFW for dissimilar titanium alloys in aerospace applications.