Non-destructive evaluation of bulk material zones and interfaces in powder bed fusion additive manufactured Ti6Al4V

Abstract

Inconsistency of equipment and inappropriate design in the laser powder-bed fusion additive manufacturing (LPBF-AM) process are not tightly related to the technology development and are more challenging to avoid. Those processing-related factors can introduce sudden changes in the products' local mechanical properties by internal flaws or microstructure variation. The different property zones and their interfaces will accumulate stress and decrease lifetime. In this work, we applied ultrasound elastography and density profile to evaluate an LPBF Ti6Al4V sample with three property zones induced by different laser speeds to represent equipment errors or inappropriate designs. The elastography clearly distinguished three zones and their corresponding dynamic properties. The ultrasound estimated density profile conforms with profilometer-determined values. The interfaces in the Ti64 sample between the zones were further discerned experimentally by ultrasound to determine the spatial and contrast distributions with a subwavelength resolution based on numerical simulations. The spatial profile and the contrast ratio on the upper boundary of the interface showed the correlation between the interface thickness and the cooling condition during the manufacturing process. These interfacial contrasts in mechanical properties within the bulk 3D printed material are challenging to detect by conventional non-destructive techniques.