Radiographic Visibility Limit of Pores in Metal Powder for Additive Manufacturing

Abstract

The quality of additively manufactured (AM) parts is determined by the applied process parameters used and the properties of the feedstock powder. The influence of inner gas pores in feedstock particles on the final AM product is a phenomenon which is difficult to investigate since very few non-destructive measurement techniques are accurate enough to resolve the micropores. 3D X-ray computed tomography (XCT) is increasingly applied during the process chain of AM parts as a non-destructive monitoring and quality control tool and it is able to detect most of the pores. However, XCT is time-consuming and limited to small amounts of feedstock powder, typically a few milligrams. The aim of the presented approach is to investigate digital radiography of AM feedstock particles as a simple and fast quality check with high throughput. 2D digital radiographs were simulated in order to predict the visibility of pores inside metallic particles for different pore and particle diameters. An experimental validation was performed. It was demonstrated numerically and experimentally that typical gas pores above a certain size (here: 3 to 4.4 µm for the selected X-ray setup), which could be found in metallic microparticles, were reliably detected by digital radiography.

Advanced Characterization and On-Line Process Monitoring of Additively Manufactured Materials and Components

“…A review paper on the subject is also published in this Special Issue [4]. Moreover, advanced imaging techniques, in particular laboratory and synchrotron X-ray computed tomography, are used to disclose the defects generated by AM processes and some strategies for their mitigation [5][6][7].…”

Radiographic testing of 3D-printed thermoplastics using Am-241 as a gamma-ray source

“…XCT is timedemanding and only works with small amounts of feedstock powder, usually a few milligrams. For varied pore and particle dimensions, 3D digital radiographs were simulated to estimate the visibility of pores inside metallic particles; a validation experiment was carried out [17]; it was shown numerically and experimentally that typical gas pores in metallic microparticles larger than a particular size (here: 3 to 4.4 μm for the selected x-ray setup) could be successfully recognized by digital radiographs [17]. About twenty years ago, gamma radiography was developed [18] as an addition to x-ray radiography to offer a method of evaluating welded assemblies, castings, and other engineering structures in metal material to check the internal defects like cracks and blowholes by iridium-192; also, the experiences have shown that the radiation from radon or radium has high penetrating, making it particularly ideal for evaluating and examine thick casting of copper alloys or steel [19].…”