Laser welding of Ti-6.8Mo-4.5Fe-1.5Al (Timetal® LCB) alloy

Laser welding was utilized to obtain high-integrity welds in 1.5 mm thick LCB sheet. Welds were characterized by narrow fusion and heat-affected zones and a relatively fine beta grain size of about 100 mu m. Postweld heat treatment at 593 degrees C (1100 degrees F) for 4 hours resulted in fine alpha precipitation in the base and weld metals thus producing material with high strength above 1275 MPa (187 KSI) and a tow ductility of about 2%. Heat treatment at 649 degrees C (1200 degrees F) for 8 hours resulted in coarse alpha precipitation both along beta grain boundaries and in beta grain interiors. This material exhibited a lower tensile strength of about 1080 MPa (160 KSI) with higher ductility about 4%. An intermediate level of strength of about 1150 MPa (170 KSI) and significantly improved ductility exceeding 8% was achieved using a duplex heat treatment of 482 degrees C (900 degrees F) for 2 hours + 649 degrees C (1200 degrees F) for 3 hours. Fractography of the welded samples showed the fracture appearance of the fusion zone is mainly transgranular in nature for the as-welded material and intergranular in nature for the aged material. However, a mixture of dimpled type fracture and intergranular fracture mode was observed at the heat-affected zone and base metal for the aged samples.