189 research outputs found
Microstructure and Residual Stress Evolution of Laser Powder Bed Fused Inconel 718 under Heat Treatments
AbstractThe current work aimed to study the influence of various heat treatments on the microstructure, hardness, and residual stresses of Inconel 718 processed by laser powder bed fusion process. The reduction in residual stresses is crucial to avoid the deformation of the component during its removal from the building platform. Among the different heat treatments, 800 °C kept almost unaltered the original microstructure, reducing the residual stresses. Heat treatments at 900, 980, and 1065 °C gradually triggered the melt pool and dendritic structures dissolution, drastically reducing the residual stresses. Heat treatments at 900 and 980 °C involved the formation of δ phases, whereas 1065 °C generated carbides. These heat treatments were also performed on components with narrow internal channels revealing that heat treatments up to 900 °C did not trigger sintering mechanisms allowing to remove the powder from the inner channels
An investigation on the effect of deposition pattern on the microstructure, mechanical properties and residual stress of 316L produced by Directed Energy Deposition
Abstract In this work, 316L cubes were produced by Directed Energy Deposition (DED) process. To evaluate the effect of deposition patterns on the microstructure, mechanical performance and residual stress of 316L samples, two different deposition strategies are selected (67° and 90°). The general microstructure is revealed, and then the effect of deposition pattern on the microstructure of 316L alloy is evaluated through the Primary Cellular Arm Spacing (PCAS) analysis. The cooling rate in each sample is estimated according to the PCAS values. Interestingly, it is found that by increasing the rotation angle per layer, the PCAS value decreases as a consequence of increment in the cooling rate. On the other hand, in both cases, by increasing the distance from the substrate, due to the changes in cooling mechanisms, the cooling rate at first decreases and then at the last layers increases again. The phase composition analysis of 316L samples confirms the predictions that suggested the presence of residual δ-ferrite in the final microstructure. In fact, the final microstructure of samples is characterized by austenitic dendrites together with some residual δ-ferrite in the interdendritic regions. Moreover, the microstructural evaluations exhibit that during the DED process, some metallic inclusions are formed within the 316L samples that consequently deteriorates their mechanical properties. Tensile results show that the samples with 90° rotation per layer have a better mechanical performance such as slightly higher ultimate tensile strength and almost 35% higher elongation to fracture, mainly owing to their finer microstructure and slightly less oxide content. However, in both cases, the elongation of the 316L samples is lower than the typical elongation of this material produced via DED. This discrepancy is found to be as a result of higher inclusions contents in the samples produced in this work with respect to those of literature. Lastly, it is found that the residual stresses on the top surfaces are similar for both deposition patterns, although higher stress values are observed on the lateral surfaces of the cubes produce using the 90° rotation per layer
Monitoring Approach to Evaluate the Performances of a New Deposition Nozzle Solution for DED Systems
In order to improve the process efficiency of a direct energy deposition (DED) system, closed loop control systems can be considered for monitoring the deposition and melting processes and adjusting the process parameters in real-time. In this paper, the monitoring of a new deposition nozzle solution for DED systems is approached through a simulation-experimental comparison. The shape of the powder flow at the exit of the nozzle outlet and the spread of the powder particles on the deposition plane are analyzed through 2D images of the powder flow obtained by monitoring the powder depositions with a high-speed camera. These experimental results are then compared with data obtained through a Computational Fluid Dynamics model. Preliminary tests are carried out by varying powder, carrier, and shielding mass flow, demonstrating that the last parameter has a significant influence on the powder distribution and powder flow geometry
Influence of Process Parameters and Deposition Strategy on Laser Metal Deposition of 316L Powder
In blown powder additive manufacturing technologies the geometrical stability of the built parts is more complex with respect to more conventional powder bed processes. Because of this reason, in order to select the most suitable building parameters, it is important to investigate the shape and the properties of the single metal bead formation and the effect that a scan track has on the nearby ones. In the present study, a methodology to identify an appropriate laser metal deposition process window was introduced, and the effect of the building parameters on the geometry of circular steel samples was investigated. The effect of the scanning strategy on the deposited part was also investigated. This work draws the attention to the importance of the obtainment of the most suitable melt pool shape, demonstrating that the laser power and the scanning strategy have a strong influence not only on the shape but also on the mechanical properties of the final component
Proceedings of CIEC 16 European Inter-regional Conference on Ceramics - Torino, 9-11 September 2018
This e-book collects the extended abstracts of some of the oral and poster presentations, which have enlived the 16th International Inter-Regional European Conference on Ceramics, CIEC 16, held in Torino, Italy, from 9 to 11 September 2018
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
Parameters Optimization and Repeatability Study on Low-Weldable Nickel-Based Superalloy René 80 Processed via Laser Powder–Bed Fusion (L-PBF)
This work aims to investigate the processability of René 80 via laser powder–bed fusion (L-PBF). René 80 is a poorly weldable Ni-superalloy, currently processed via investment casting to fabricate turbine blades working at an operating temperature of about 850 °C. The L-PBF parameters optimization aims to increase part integrity and enhance processing repeatability. This part was tackled by creating a complete design of experiments (DOE) in which laser power, scan speed and hatching distance were varied accordingly. Optimizing the abovementioned parameters minimized the crack density and pore area fraction. Hence, five parameter sets leading to a crack density lower than 100 µm/mm2 and a pore fraction between 0.045% and 0.085% were selected. Furthermore, the intra-print repeatability was studied by producing three specimens’ repetitions for each optimal set of parameters in the same build. The porosity value obtained was constant among repetitions, and the crack density (around 75 µm/mm2) had a slight standard deviation. The third step of the research assessed the inter-prints repeatability by producing a replica of the five selected parameter sets in a different build and by comparing the results with those studied previously. According to this latter study, the porosity fraction (ca. 0.06%) was constant in intra- and inter-print conditions. Conversely, crack density was lower than 100 µm/mm2 only in three sets of parameters, regardless of the intra- or inter-build cross-check. Finally, the best parameter set was chosen, emphasizing the average flaw fraction (least possible value) and repeatability. Once the optimal densification of the samples was achieved, the alloy’s microstructural features were also investigated
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