Evaluating the spreadability of new materials during production is usually not feasible due to the cost associated with the minimum batch volume to fill in the machine and the time required to clean between each test. Studies have demonstrated the link between powder cohesiveness and spreadability. ISO/ASTM TR 52952:2023 provides a methodology to predict the spreadability of metallic powders based on the Cohesive index metric (GranuDum, Granutools). However, the spreadability was evaluated directly inside the printer which, despite the advantage of being close to the process condition, does not allow deep investigation of the mechanism leading to irregular layers.To tackle some of the limitations of the in-situ evaluation, a test bench has been developed and instrumented (LEM3, France). Powder layers are sequentially deposited, and the layer quality is evaluated between each layer. The device is instrumented with a confocal microscope used to precisely measure profiles of the height variation across the layer. The layer local topology is thus directly accessible. The results show good agreement with the previous measurements done in the printer. Furthermore, the evolution of the layer quality between the initial layers is evaluated. Indeed, we observed a rapid improvement in layer quality over the first 10 layers. This emphasizes the difference between spreading a layer over a flat bed or over previous powder layers. Therefore, multi-layers analysis are essential for proper spreadability evaluation.

Keywords: powder; cohesion; spreadability; LPBF; powder characterization