On the size-dependent fatigue behaviour of laser powder bed fusion Ti-6A1-4v

In the paper 'On the size-dependent fatigue behaviour of laser powder bed fusion Ti-6Al-4V' published in Additive Manufacturing, Jieming S. Zhang and a team from this department, the Department of Engineering, and Alloyed Limited considered two samples.

Working with two cylindrical samples of differing sizes, they observed that the larger specimen demonstrated better fatigue resistance, particularly in the high-cycle regime, with the differing surface roughness contributing to this effect.  They confirm that processing-induced porosity can compromise the fatigue performance even when the initiation sites are surface defects.

The larger contribution of porosity to the fatigue fracture process of the larger specimen resulted in a higher scatter in the fatigue life.  Differences in microstructure did not seem to contribute strongly to the variation in fatigue properties over the two specimens, however the authors present some evidence that the coarser microstructure of the larger specimen promotes a stronger tolerance to defects and induces more tortuous crack paths which hinders fatigue crack growth.