The orientation effect on cyclic deformation of laser powder bed fusion

A Magnification of the microstructure, and a plot of the build orientation measured against the texture index

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 75o 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 30o 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 45o, cracks began to initiate from the otherward-facing surface owing to the reduced variation in Ra 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 75o specimen whereas the difference in crack initiation sites of the 45o 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.