Application of mechanical surface finishing processes for roughness reduction and fatigue improvement of additively manufactured Ti-6Al-4V parts

Currently, additively manufactured (AM) parts have a high initial surface roughness after the manufacturing process, which can be a limitation for application in highly stressed and cyclically loaded areas. In the present study, Ti-6Al-4V samples were manufactured by laser beam melting, annealed and hot isostatically pressed afterwards. They showed an initial surface roughness of Ra = 17.9 μm depending on their build direction (45°). Subsequently, four different mechanical surface finishing processes were applied separately on plates and fatigue coupons in order to reduce the surface roughness: Milling, blasting, vibratory grinding and a micro machining process. The effectiveness of each treatment is evaluated with respect to the surface topography, as well as the fatigue properties based on axial fatigue tests performed in accordance to DIN EN 6072. The initial roughness could often be reduced to values Ra < 1 μm. The roughness decrease led to a substantial increase in the fatigue performance from initially 300 MPa to a maximum of 775 MPa (after 3 × 107 cycles).