The orientation effect on cyclic deformation of laser powder bed fusion

The authors* of 'Orientation matters: assessing the cyclic deformation behaviour of laser powder bed fusion Ti-6Al-4v' as published in Materials & Design explain their analysis and rationalisation of the orientation dependency of the fatigue behaviour of laser powder bed fusion Ti-6Al-4V (they studied seven build orientations relative to the build plate).

The 75^o specimen demonstrated that the highest fatigue life was due to the optimal surface quality and low proportions of grains near-parallel to the loading direction.  They observed that when the build orientation was 30^o or below, only defects on the downward-facing surface served as the fatigue crack initiation sites as a result of the poor surface quality.  Beyond 45^o, cracks began to initiate from the otherward-facing surface owing to the reduced variation in R_a across the sample surface.  The large variation in the size and number of pore clusters near the initiation site governed the highest fatigue scatter of the 75^o specimen whereas the difference in crack initiation sites of the 45^o specimen resulted in the large difference in fatigue life.

The results demonstrate that the orientation effect is a critical factor to consider for the design of fatigue-tolerant intricate components.

* Led by this department, in collaboration with the Department of Engineering (Oxford), the University of Birmingham and Alloyed Limited.