Microstructure Evolution and Interface Integrity in Additively Manufactured Repair Builds of Ti-5553

Titanium alloys are widely used in aerospace applications due to their high specific strength and corrosion resistance. The repair and remanufacturing of such high-value components offer significant potential as an alternative to full component replacement, supporting circular economy and sustainable manufacturing strategies. Additive manufacturing (AM), particularly Laser Powder Bed Fusion (LPBF), offers an advance route for repair and remanufacturing through material deposition onto existing components. Among titanium alloys, the metastable β alloy Ti-5Al-5Mo-5V-3Cr (Ti-5553) is of particular interest due to its high strength and wide heat treatment window. However, limited understanding exists regarding its behavior during AM-based repair, especially when deposition occurs on substrates with different prior thermal histories and microstructural states.
This thesis investigates the microstructural evolution and mechanical response of interfaces formed when Ti-5553 is deposited onto existing Ti-5553 substrates using LPBF, including additively manufactured and suction-cast substrates, under as-built and heat-treated conditions. Microstructural characterization was performed using optical microscopy, scanning electron microscopy, and electron backscatter diffraction, while mechanical behavior was assessed through microhardness mapping and tensile testing. The results show that LPBF produces continuous columnar β grains across the interface, indicating sound metallurgical bonding without observable defects. Microhardness distributions were generally uniform across interfaces for similar processing conditions. The heat-treated specimens exhibited increased hardness (370±10 HV compared to 310±8 HV for as-built samples) due to fine α-phase precipitation. Tensile testing demonstrated preserved interfacial integrity, with strengths of 840±20 MPa and 19±3% elongation for as-built and 1170±35 MPa with 10±2% elongation for heat-treated conditions. Predominantly ductile fracture behavior was observed in all the samples. Overall, the findings demonstrate that LPBF enables effective deposition of Ti-5553 onto existing substrates, supporting the feasibility of AM-based repair.