IS SURFACE FINISH REALLY DECISIVE FOR THE FATIGUE OF ADDITIVELY MANUFACTURED Ti ALLOY?

Powder bed techniques of additive manufacture, where the built product is surrounded by a loose powder, yield low-quality surfaces. The powder particles that are in a close contact with the product adhere to its surface, either by thermal diffusion effects or by partial melting by contour scan tracks. The surface of additively manufactured metals has been shown to negatively affect mechanical properties, with the most negative impact on fatigue. Besides, these particles can loosen and cause problems during part operation. With respect to the above-mentioned problems, different ways of surface finish have been applied. In this study, we tested the samples of the Ti6Al4V alloy prepared by selective laser melting with three different surface finishes (asbuilt, machined and machined + tumble polished), and subjected them to high-cycle fatigue tests. Although many authors have reported on the positive effect of a surface finish on fatigue, in this study, we show that it might not always be true.