1,720,968 research outputs found
Analysis, numerical modelling and experimental investigation of Laser Powder Directed Energy Deposition (LP-DED) process
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Development of a simulation framework for AM process consideration in industrial production
No full textAn investigation on the effect of deposition pattern on the microstructure, mechanical properties and residual stress of 316L produced by Directed Energy Deposition
Full text linkIn 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
Evaluation of Porosity in AISI 316L Samples Processed by Laser Powder Directed Energy Deposition
Full text linkDirected energy deposition-laser beam/powder (DED-LB/Powder) is an additive manufacturing
process that is gaining popularity in the manufacturing industry due to its numerous
advantages, particularly in repairing operations. However, its application is often limited to case
studies due to some critical issues that need to be addressed, such as the degree of internal porosity.
This paper investigates the effect of the most relevant process parameters of the DED-LB/Powder
process on the level and distribution of porosity. Results indicate that, among the process parameters
examined, porosity is less affected by travel speed and more influenced by powder mass flow rate and
laser power. Additionally, a three-dimensional finite element transient model was introduced, which
was able to predict the development and location of lack-of-fusion pores along the building direction
On the effect of part orientation on stress distribution in AlSi10Mg specimens fabricated by Laser Powder Bed Fusion (L-PBF)
Full text linkThe freedom of design of AM products suffers from some limitations in case of powder bed metal processes, because AM part's integrity is affected by the residual stress state that is a consequence of the thermal history during part fabrication. Aim of this work is to evaluate the effect of part orientation on stress distribution. Thus, flat samples of AlSi10Mg alloy built along different orientations are produced by means of laser powder bed fusion (L-PBF) process, also known as Selective Laser Melting (SLM). Then, the semi-destructive hole-drilling method is used to evaluate residual stresses beneath the surfaces of samples. The outcomes of the study can be exploited to define design rules in order to both minimize support structures and optimize the orientation of the part in the building volume
Heat-Treated Inconel 625 by Laser Powder Bed Fusion: Microstructure, Tensile Properties, and Residual Stress Evolution
Full text linkThis work investigates the impact of different heat treatments on the evolution of the microstructure, tensile properties, and residual stresses of Inconel 625 (IN625) processed by laser powder bed fusion (LPBF). Applying a heat treatment is an essential step to mitigate the high residual stresses in the components produced by LPBF and, simultaneously, to design the mechanical properties of the components. A high magnitude of residual stress can involve deformation and reduce the fatigue resistance of the components. In the current work, heat treatments performed at 600, 800, and 870 degrees C provided minimal modification on the dimensions of the grains but involved the formation of new phases, which increased the tensile strength. The results showed mitigation of the residual stresses at 800 and 870 degrees C correlated with the formation of Cr-rich M23C6 carbides and delta phases, respectively. Finally, the solution annealing at 1150 degrees C triggered recrystallization with the formation of sub-micrometric carbides, reducing the residual stresses. The solution annealing treatment involved an improvement of the ductility and a reduction in tensile strength. This work provides a guide to understanding the microstructure, residual stress, and mechanical properties evolution of the IN625 alloy under heat treatments
Machining induced residual stresses in AlSi10Mg component produced by Laser Powder Bed Fusion (L-PBF)
No full textAnalyzing the Interplay of Sintering Conditions on Microstructure and Hardness in Indirect Additive Manufacturing of 17-4PH Stainless Steel
No full textIndirect additive manufacturing (AM) methods have recently attracted attention from researchers thanks to their great potential for cheap, straightforward, and small-scale production of metallic components. Atomic diffusion additive manufacturing (ADAM), a variant of indirect AM methods, is a layer-wise indirect AM process recently developed based on fused deposition modeling and metal injection molding. However, there is still limited knowledge of the process conditions and material properties fabricated through this process, where sintering plays a crucial role in the final consolidation of parts. Therefore, this research, for the first time, systematically investigates the impact of various sintering conditions on the shrinkage, relative density, microstructure, and hardness of the 17-4PH ADAM samples. For this reason, as-washed samples were sintered under different time-temperature combinations. The sample density was evaluated using Archimedes, computed tomography, and image analysis methods. The outcomes revealed that sintering variables significantly impacted the density of brown 17-4PH Stainless Steel samples. The results indicated more than 99% relative densities, higher than the value reported by Markforged Inc. (similar to 96%). Based on parallel porosities observed in the computed tomography results, it can be suggested that by modifying the infill pattern during printing, it would be possible to increase the final relative density. The microhardness of the sintered samples in this study was higher than that of the standard sample provided by Markforged Inc. Sintering at 1330 degrees C for 4 h increased the density of the printed sample without compromising its mechanical properties. According to X-ray diffraction analysis, the standard sample provided by Markforged Inc. and "1330 degrees C-4 h" one had similar stable phases, although copper-rich intermetallics were more abundant in the microstructure of reference samples. This study is expected to facilitate the adoption of indirect metal AM methods by different sectors, thanks to the high achievable relative densities reported here
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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