Improved fatigue strength of AM Ti6Al4V by surface post-processing

Magnus Kahlin ^1,2, Hans Ansell ^1,2, Johan Moverare ² 

 ¹Saab AB, ²Linköping University 

The fatigue strength of L-PBF and E-PBF Ti6Al4V with rough as-built surface is generally 
dominated by the rough surface rather than by internal defects. Consequently, the surface 
roughness needs to be improved before additively manufactured parts should be 
introduced to critical structural aerospace applications. Additively manufactured Ti6Al4V 
subjected to hot isostatic pressing and machining can achieve similar fatigue strength as 
conventional wrought material.  
However, parts that require machining of all surfaces will be limited to traditional 
machining geometries without the benefits of a freeform additively manufactured part. In 
order to increase the fatigue strength while maintaining a complex design, L-PBF and E-PBF 
Ti6Al4V were subjected to five surface post-processing methods: shot peening, laser shock 
peening, centrifugal finishing, laser polishing or linishing.  

The fatigue strength was increased with over 100% for both L-PBF and E-PBF material but 
only shot peened or centrifugal finished L-PBF material achieved comparable fatigue 
strength to conventional wrought material.  

Moreover, the surface roughness alone was not found to be a sufficient indicator of fatigue 
strength. The final fatigue strength after post-processing depends instead of a combination 
of surface roughness, residual stress, microstructure and remaining subsurface defects. 

Open access papers available at International Journal of Fatigue: 
https://doi.org/10.1016/j.ijfatigue.2020.105497
https://doi.org/10.1016/j.ijfatigue.2020.105945