Effects of the Additive Manufacturing DMLM Process on Metal Powder: Changes, Contaminations and Reuse for the Aerospace Industry

The aim of this master thesis is articulated into two main objectives: first, to assess the evolution of Inconel 718 powder properties over multiple reuse cycles in the Direct Metal Laser Melting (DMLM) Additive Manufacturing process; and second, to evaluate the influence of different recoater blade materials, hard versus soft, on powder contamination and component quality. This thesis focuses on two primary research goals: the first one is to characterize the progressive changes in Inconel 718 powder properties resulting from multiple reuse cycles in the Direct Metal Laser Melting (DMLM) process; and (2) to examine the impact of recoater blade material selection, comparing hard and soft blades, on powder chemical and morphology integrity and final part quality. Powder reuse is becoming increasingly important in metal additive manufacturing due to its considerable economic implications. However, powder must be carefully monitored after each reuse cycle, as repeated use can lead to significant changes in physical, chemical, and flow properties, potentially compromising process stability and final part quality. To investigate this, two production batches were analyzed: Batch 80, monitored from the virgin state through six reuse cycles, and Batch 76, examined between reuse cycles 22 and 23 following an anomalous oxidation event. Several powder characteristics were studied, including particle size distribution (PSD), SEM morphology, flowability, skeletal density, and chemical composition, with particular attention to oxygen content. These analyses allowed for the identification of trends and degradation mechanisms that may affect powder performance over time. The second part of the study focuses on the effect of recoater blade material on the powder spreading process and component buildability. The hard recoater blade is known to induce certain process limitations, such as increased risk of component deformation due to its rigidity. Conversely, the soft recoater blade, investigated as a potential alternative, reduces mechanical interaction but introduces new risks, such as contamination and uneven spreading, so factors that can degrade the powder bed and affect build quality. Understanding the trade-offs between these two recoater blade types is crucial for optimizing DMLM process parameters and ensuring consistent manufacturing quality. This work was developed in collaboration with Politecnico di Torino and GE Avio Aero, a leading company in the field of metal additive manufacturing. In 2017, GE Avio Aero, together with the Politecnico di Torino, established the Turin Additive Laboratory (TAL), which has since become a key center for research and innovation in AM technologies.