Understanding the Effects of Surface Finish on the Fatigue Performance of Additive Manufactured Aerospace Components
Authors:   , Ednie Lauren 
Published: June 2024

Additive manufacturing (AM) is an advanced manufacturing technique whose uptake within the aerospace industry is thought to be a key driver to reaching the UK imposed 2050 Net-Zero targets. This is being driven by the advantages that the use of AM could unlock, including but not limited to, cost savings through reduced material usage, the ability to produce components with an increased geometrical complexity and the removal of bottlenecks within conventional manufacturing processes due to reduced manufacturing times. Whilst AM can unlock numerous advantages across multiple industries, its uptake is currently being limited due to several challenges and an uncertainty within the AM mechanical performance. One of the main challenges that is being tackled is that there is currently a limited understanding of the effects of the inherent surface roughness that is seen within AM built components and the effects of this surface roughness on a component’s mechanical performance, predominantly the cyclic fatigue properties. One of the main advantages AM could unlock would be the ability to build components ready for direct placement within larger systems, but there are a number of issues that hinder this. One of the main reasons that hinder the further adoption of these methods is the high-surface roughness seen within as-built AM components. It is this high surface roughness that is thought to be the primary reason for the knockdown seen in AM fatigue performance. When coupled with inherent differences in the microstructure and build orientation effects, this knockdown when compared to the performance of conventional material is significant. Therefore, there is a need to fully understand the effects of surface roughness on the fatigue properties and the methods of surface finishing that could be applied to maximise the fatigue performance of AM material, without nullifying the benefits of this manufacturing method. Within this study the effects of the inherent AM surface roughness on the high cycle fatigue (HCF)performance of the titanium (Ti) alloy Ti-6Al-4V manufactured using various AM methods will be explored. This will include samples manufactured using Electron Beam Melting (EBM), Laser Powder Bed Fusion (LPBF) and Laser-Metal Deposition with Wire (LMD-w), with samples in both the as-built and the machined & polished condition. In addition to this the impact of build orientation will also be explored, with samples built in both the horizontal (0º) and vertical (90º) orientations. The HCF test results will be supported by advanced surface profilometry, microstructural, defect and fractographic analysis. The HCF test results alongside advanced surface profilometry, microstructural, defect and fractographic analysis revealed that whilst the surface roughness in the majority of instances is the primary factor impacting the fatigue performance on AM material, it cannot be considered alone. It was found that the inherent as-built surface finish of AM material resulted in an increased number of stress-raising features upon the surface of a sample, leading to a reduction in the samples’ fatigue life, whilst machined & polished material failed due to the presence of internal features. Statistical analysis of the results gained was also carried out to allow for the determination of a sample’s fatigue life outside of the testing regime completed within this work.