Surface improvement of laser powder bed fusion processed Ti6Al4V for fatigue applications

Abstract

• Effect of wet-chemical etching of LPBF Ti6Al4V using 5%HF+10%HNO 3 solution on surface quality and fatigue properties was studied. • Etching results in 5-fold reduction in average roughness (from 32.7 to 6.4 µm), leading to a 2-fold increase in fatigue endurance limit (from 150 MPa to 300 MPa). • The effect is highly consistent on complex geometrical surfaces, as demonstrated in case of AM lattice structure. Laser Powder Bed Fusion holds significant potential for the manufacturing of highly complex Ti6Al4V structural components, however the as-produced surface roughness severely limits the fatigue life of components. To reduce the effect of high surface roughness, post processing methods applicable to all geometries are desired. In this study wet-chemical etching methods were examined with regard to fatigue performance. Wet-chemical etching techniques with hydrofluoric acid-containing solutions were assessed for the change in surface condition, material loss, and resultant fatigue response across a range of chemical etchants, with reference to the as-built and machine finished states. Hydrofluoric and nitric acid containing solutions proved to be effective in reducing average surface roughness R a from 32.7 µm to 6.4 µm, and doubling the effective fatigue endurance limit from 150 MPa to 300 MPa.