Directionality of Cavities and Porosity Formation in Powder-Bed Laser Additive Manufacturing of Metal Components Investigated Using X-Ray Tomography

Abstract

Ensuring additive manufactured metal components are free of major defects is crucial to the application of this new technology in medical and aerospace industries. One source of defects in such parts is lack of fusion in individual locations or specific layers. Such lack of melting or fusion could be the result of a nonflat powder bed due to an imperfect recoating blade or loose support structures causing recoating problems. Another possible source is laser power fluctuations or beam size fluctuations, or even ambient humidity or temperature changes, among others. The aims of this article are to investigate lack of fusion with planned induced defects (cavities) with different three-dimensional (3D) geometries and analyze these using nondestructive 3D X-ray tomography. It is found that some fusion occurs in induced defect layers and lines perpendicular to the build direction (XY) up to 180 μm in height. This means fusion occurs through fused layers above cavities, minimizing defect formation in the plane of the build platform. In contrast, in the case of vertical cavities (cavity walls) parallel to the build direction, much larger defects are observed compared to the above case. This result may point to the build direction (vertical) being more favorable for porosity formation under nonideal conditions (i.e., a preferred directionality). An example of unexpected porosity trail formation in the build direction is also reported from such nonideal conditions for a real part in contrast to a designed cavity.