The effect of diffusion bonding (DB) defect with φ 4mm and φ 2mm diameter on mechanical porperties of Ti-6Al-4V alloy is investigated. The defect plane is parallel to the load axis

the strength and ductility of the material are not affected because the area subjected to tensile load almost stayed the same. Ti-6Al-4V alloy with φ 4mm DB defect under fully reversed fatigue load exhibited a large scatter of life

and the defect is not the unique crack initiation area. Samples with surface crack initiation exhibited longer fatigue life; while almost all samples with defect-induced crack initiation exhibited a much shorter fatigue life. Finite element analysis shows that the stress concentration is lower when the defect is in center; The stress concentration is higher when the defect is on edge.