Ti-6Al-4V L-PBF chemically etched components: from the surface micro-geometric characteristics to the fatigue strength

Abstract

Additive manufacturing is nowadays already used on aeronautical serial parts but very few of them are highly loaded critical components. Titanium alloy Ti-6Al-4V and laser powder bed fusion (L-PBF) manufacturing process are both part of the most studied materials and processes. Many studies have been dedicated to L-PBF produced Ti-6Al-4V on a large range of subjects from defect generation and microstructure evolution to fatigue life. Finishing processes are also a significant part of the studied processes as the micro-geometry of additively manufactured components remains the principal drawback for the production of fatigue subjected critical parts. In this work, fatigue bending tests are undertaken on Ti-6Al-4V L-PBF made coupons. For each of them, the loaded surface has been scanned using an optical proflometer to identify the population of micro-geometric surface features. The effect of a chemical etching process on this population is described and the killer feature is highlighted in the population. Different indicators are discussed to understand if and how the killer feature can be predicted, knowing the loading conditions. It is concluded that Murakami's √area parameter may not be sufficient to determine the critical surface feature. A large scatter is observed in the fatigue strength, however, an approach based on the stress intensity range seems the most appropriate to identify the potentially critical surface micro-geometric features from the characterized population.