Influence of contour strategy and chemical immersion on the surface characteristics and mechanical behaviour of electron beam powder bed fusion Ti-6Al-4 V

Parts produced via electron beam powder bed fusion often exhibit higher lateral surface roughness relative to other metal-based powder bed processes due to partially sintered powder and the inherent layered building process. Increased roughness acts as stress concentrators that degrade mechanical performance, particularly fatigue life, and detached sintered particles can exacerbate tribological wear. While post-processing methods such as machining and surface grinding are commonly employed to mitigate these effects, alternative strategies are of interest, especially when conventional methods cannot be used to treat complex part geometries fabricated via additive manufacturing. This study investigates continuous contouring as an in-process strategy to modify surface morphology, alongside chemical immersion in hydrofluoric (HF) and nitric (HNO₃) acid as a post-processing treatment. Surface roughness was characterised using optical profilometry and SEM, and tensile and fatigue properties were evaluated under axial loading. Continuous contours showed broadly comparable amplitude-type roughness values (Ra, Rq, Rz, Rp) to multispot, though with a higher mean spacing Rsm (425 μm vs. 304 μm). Chemical immersion reduced most roughness parameters by about 33% for multispot and 24% for continuous contours. The combined use of continuous contouring and chemical immersion produced modest improvements in tensile strength, ultimate tensile strength, and ductility, but significantly enhanced fatigue resistance as chemically immersed continuous samples exhibited a mean fatigue life 64% longer than as-built samples (sinusoidal loading, σmax = 275 MPa, σmin = 27.5 MPa and R = 0.1).