On the effect of internal channels and surface roughness on the high-cycle fatigue performance of Ti-6Al-4V processed by SLM

Publication date: 5 April 2018
Source:Materials & Design, Volume 143
Author(s): Johannes Günther, Stefan Leuders, Peter Koppa, Thomas Tröster, Sebastian Henkel, Horst Biermann, Thomas Niendorf
Selective laser melting (SLM) is an additive manufacturing process allowing for the production of metallic high performance materials and components with complex geometries. Therefore, possible applications are direct production of casting molds, tools or turbine blades with internal cooling channels for an optimized cooling efficiency. A disadvantage of the technology is the process-inherent surface roughness, which is critical especially under fatigue loading conditions. Since internal surfaces often cannot be smoothened due to limited accessibility, the objective of this study is to assess the fatigue properties of Ti-6Al-4V samples designed with internal axial channels featuring a rough as-built surface. Samples with various diameters and numbers of channels have been tested not always exhibiting a deterioration of the fatigue performance compared to solid samples. Subsequent fractography by scanning electron microscopy revealed distinct failure mechanisms. Besides the fatigue crack initiation on features of the unmodified internal surfaces, residual porosity in the bulk, i.e. lack-of-fusion defects, keyhole defects and gas pores, respectively, could be identified as crack origin. Relatively low scatter of fatigue lives found is attributed to rapid crack initiation and, thus, the dominant influence of the (micro-) crack growth regime.

Graphical abstract

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