Project Overview
The RePowder project aims to develop a comprehensive process for recycling Inconel-alloy scraps to produce atomized powder for additive manufacturing. This project focuses on procuring and qualifying Inconel-alloy scraps for atomization to produce powder batches with specific grades and compositions. These powders will be used for additive manufacturing of lab-scale and real component bulk samples, which will undergo rigorous testing, especially for mechanical fatigue at high temperatures. This testing is crucial for qualifying Inconel-alloy components.
Key Objectives:
- L-PBF Process Parameter Development: Tailoring specific L-PBF process parameters to influence the microstructure and defectiveness of the material.
- Durability Assessment: Comparing the fatigue strength of components produced from recycled powder to those made from conventional powder.
- Powder Recycling Methodology: Developing a baseline methodology for recycling critical metallic materials.
Scientific Community Reinforcement
This highly interdisciplinary research project is carried out by a closely integrated consortium, including the University of Trento (Prof. Matteo Benedetti, PI), the University of Pisa (Prof. Bernardo Monelli, Vice PI), and F3nice company, which has expertise in recycling scrap materials for additive manufacturing.
The project contributes to a sustainable society through green additive manufacturing technologies, aiming to reduce the carbon footprint of AM processes significantly, a cornerstone of Industry 5.0. The adoption of additively manufactured Inconel components in the energy and aerospace industries could enhance the efficiency of gas and steam generators by enabling the creation of intricate internal cooling channels, thus increasing the safe operating temperature range.
Progress Beyond the State of the Art
The results of the project will provide a baseline for the knowledge necessary to the industrial adoption of recycled Inconel 718 in critical components. A methodology will be proposed to use Inconel scrap from conventional processes to produce powder particles for use in Laser Powder Bed Fusion (L-PBF). Microstructure, internal defects, static, and fatigue properties for specimens produced from recycled and virgin powder will be compared.
This project will help in creating a circular economy for the conventional manufacturing process and reduce the cost of AM processes, therefore it is fully coherent with the strategic sector of ensuring security of supply in raw materials, achieved through breakthrough technologies in areas of advanced solutions for substitution, resource and energy efficiency, effective reuse and recycling of critical raw materials.
Components are being produced using a Renishaw RenAM 500S Flex SLM machine, installed in the “Metal Additive Manufacturing” laboratory of the University of Pisa. Figure 1 shows the printed Inconel 718 samples at UniPi.
The RePowder project investigates various powder batches:
- Conventional Powder: having the nominal chemical composition and Particle Size Distribution (PSD), D10 = 15μm – D90 = 53μm, adopted for the L-PBF process
- Rejected Powder: Powder from failed L-PBF and EBM processes.
- Clean Scrap Recycling: Deep cleaned scrap producing powder with no material or oil contamination.
- Industrial Scrap Recycling: Scrap from conventional machining operations, subjected to oil-removing treatments.
- Blended Powder: Combination of conventional and recycled powder.
- Re-recycled Powder: Powder subjected to multiple recycling cycles.
Characterization and Calibration
Recycled and conventional powders are characterized for particle distribution size, shape, flowability, and chemical composition using SEM microscopy, EDX chemical analysis. Special attention is given to how powder blending affects flowability. The L-PBF process parameters such as laser power, scan velocity, beam spot size, and layer thickness are calibrated for recycled powder.
Post-Processing and Metallurgical Analysis
Components made from Inconel 718 using L-PBF undergo post-processing aging treatments tailored to their chemical and physical properties. Metallurgical characterization includes examining microstructure and defects (porosity, lack of fusion, hot-cracks) through metallographic examinations and microstructural investigations using optical and scanning electron microscopy.
Renishaw RenAM 500S Flex
| Laser power | 500 W |
| Build volume | 250 x 250 x 350 mm |
| Layer thickness | 20 ÷ 100 μm |
| Dynamic focus diameter | 80 ÷ 500 μm |
| Platform temperature | Up to 170°C |
| User defined process parameters | > 130 |
| Powder sieving | External sieving station |
https://www.youtube.com/watch?v=ywTw5ziiTdk
Publications
Paper on International Journal of Fatigue :: Open Access
https://doi.org/10.1016/j.ijfatigue.2025.108821
This study models the impact of surface roughness and pores on the fatigue strength of plain and V-notched Inconel 718 specimens produced via laser powder bed fusion, in both as-built and machined conditions. Fractographic analysis assessed porosity, while surface roughness was examined using an optical profilometer. Pore size and distance from the external surface were analyzed using Gumbel and exponential distribution functions. Finite element simulations of scanned surface profiles and pores were implemented, and the results were employed to calculate the fatigue stress concentration factors according to the theory of critical distances. This latter was calibrated by using the sharp and blunt V-notched specimens under machined condition. Finally, extreme value distributions were applied to estimate fatigue stress concentration factors of pores and surface roughness at 99% of probability. These latter were combined in a simplified way, and fatigue strength predictions of blunt V-notched as-built and plain machined and as-built specimens closely matched experimental data.
