Evaluation of a Laboratory-Scale Gas-Atomized AlSi10Mg Powder and a Commercial-Grade Counterpart for Laser Powder Bed Fusion Processing

Laser powder bed fusion (LPBF) is an additive manufacturing technology that implies using metal powder as a raw material. The powders suitable for this kind of technology must respect some specific characteristics. Controlled gas atomization and post-processing operations can strongly affect the final properties of the powders, and, as a consequence, the characteristics of the bulk components. In fact, a complete characterization of the powders is mandatory to fully determine their properties. Beyond the most used tests, such as the volume particle size distribution (PSD) and flowability, the PSD number, the Hausner ratio and the oxidation level can give additional information otherwise not detectable. The present work concerns the complete characterization of two AlSi10Mg powders: a commercial-grade gas atomized powder and a laboratory-scale gas atomized counterpart. The laboratory-scale gas atomization allows to better manage the amount of the fine particles and the oxidation level. As a consequence, a higher particle packing can be reached with an increase in the final density and tensile strength of the LPBF bulk samples

Critical Features in the Microstructural Analysis of AISI 316L Produced By Metal Additive Manufacturing

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Hardness Evolution of Solution-Annealed LPBFed Inconel 625 Alloy under Prolonged Thermal Exposure

Thanks to its high weldability, Inconel 625 (IN625) can be easily processed by laser powder bed fusion (LPBF). After production, this alloy is typically subjected to specific heat treatments to design specific microstructure features and mechanical performance suitable for various industrial applications, including aeronautical, aerospace, petrochemical, and nuclear fields. When employed in structural applications, IN625 can be used up to around 650 °C. This limitation is mainly caused by the transformation of metastable γ″ phases into stable δ phases occurring under prolonged thermal exposure, which results in drastically reduced ductility and toughness of the alloy. Because the microstructure and mechanical properties change during thermal exposure, it is essential to study the material simulating possible service temperatures. In the current study, LPBFed IN625 samples were solution-annealed and then subjected to thermal exposure at 650 °C for different times up to 2000 h. The characterization focused on the evolution of the main phases, γ″ and δ phases, and their influence on the hardness evolution. The microstructure and hardness of the heat-treated LPBFed IN625 samples were compared with data related to the traditionally processed IN625 alloy (e.g., wrought state) reported in the literature

Application of Directed Energy Deposition-Based Additive Manufacturing in Repair

In the circular economy, products, components, and materials are aimed to be kept at the utility and value all the lifetime. For this purpose, repair and remanufacturing are highly considered as proper techniques to return the value of the product during its life. Directed Energy Deposition (DED) is a very flexible type of additive manufacturing (AM), and among the AM techniques, it is most suitable for repairing and remanufacturing automotive and aerospace components. Its application allows damaged component to be repaired, and material lost in service to be replaced to restore the part to its original shape. In the past, tungsten inert gas welding was used as the main repair method. However, its heat affected zone is larger, and the quality is inferior. In comparison with the conventional welding processes, repair via DED has more advantages, including lower heat input, warpage and distortion, higher cooling rate, lower dilution rate, excellent metallurgical bonding between the deposited layers, high precision, and suitability for full automation. Hence, the proposed repairing method based on DED appears to be a capable method of repairing. Therefore, the focus of this study was to present an overview of the DED process and its role in the repairing of metallic components. The outcomes of this study confirm the significant capability of DED process as a repair and remanufacturing technolog

Revisiting heat treatments for additive manufactured parts: a case study of A20X alloy

A20X (Al-Cu-Ag-Mg-TiB2) is a precipitation hardening alloy, recently developed for additive manufactur ing processing. Printed parts of A20X alloy are usually post-processed with a long T7 heat treatment for improved mechanical properties with respect to its as-built counterparts. However, in the present inves tigation, it was demonstrated that T7 might not be the best suitable heat treatment available for A20X alloy. A detailed microstructural characterization of A20X samples processed with laser powder bed fusion and post-processed with T7 was carried out. Microstructural features were analysed in terms of grain size, precipitate size, phase quantification, dislocation density and width of the precipitate free zones. After the analysis, a simple and rapid heat treatment was proposed which significantly improved the mechanical properties. The yield strength (YS), ultimate tensile strength (UTS) and elongation to frac ture (e) for the T7 heat treatment were 370 ± 9 MPa, 435 ± 13 MPa and 7.3 ± 0.3 % respectively. With the proposed heat treatment, an increment of 7.1 % in YS, 6.3 % in UTS and 45 % in e was witnessed. This exceptional improvement in the mechanical behaviour has been associated with the absence of grain boundary cracking in the proposed heat treatmen

Short Heat Treatments for the F357 Aluminum Alloy Processed by Laser Powder Bed Fusion

Conventionally processed precipitation hardening aluminum alloys are generally treated with T6 heat treatments which are time-consuming and generally optimized for conventionally processed microstructures. Alternatively, parts produced by laser powder bed fusion (L-PBF) are characterized by unique microstructures made of very fine and metastable phases. These peculiar features require specifically optimized heat treatments. This work evaluates the effects of a short T6 heat treatment on L-PBF AlSi7Mg samples. The samples underwent a solution step of 15 min at 540 °C followed by water quenching and subsequently by an artificial aging at 170 °C for 2-8 h. The heat treated samples were characterized from a microstructural and mechanical point of view and compared with both as-built and direct aging (DA) treated samples. The results show that a 15 min solution treatment at 540 °C allows the dissolution of the very fine phases obtained during the L-PBF process; the subsequent heat treatment at 170 °C for 6 h makes it possible to obtain slightly lower tensile properties compared to those of the standard T6. With respect to the DA samples, higher elongation was achieved. These results show that this heat treatment can be of great benefit for the industry

Single Scans of Ti-6Al-4V by Directed Energy Deposition: A Cost and Time Effective Methodology to Assess the Proper Process Window

Directed energy deposition is an additive manufacturing technology which usually relies on prototype machines or hybrid systems, assembled with parts from different producers. Because of this lack of standardization, the optimization of the process parameters is often a mandatory step in order to develop an efficient building process. Although, this preliminary phase is usually expensive both in terms of time and cost. The single scan approach allows to drastically reduce deposition time and material usage, as in fact only a stripe per parameters combination is deposited. These specimens can then be investigated, for example in terms of geometrical features (e.g. growth, width) and microstructure to assess the most suitable process window. In this work, Ti-6Al-4V single scans, produced by means of directed energy deposition, corresponding to a total of 50 different parameters combinations, were analyzed, focusing on several geometrical features and relative parameters correlations. Moreover, considering the susceptibility of the material to oxygen pick-up, the necessity of an additional shielding gas system was also evaluated, by comparing the specimens obtained with and without using a supplementary argon flow. A process window, which varies according to the user needs, was found together with a relationship between microstructure and process parameters, in both shielding scenarios