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

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Cholesterol granulomas nasal polyp in sphenoethmoid recess. An atypical aspect in a common lesion

Nasal polyp is a non neoplastic lesion of the respiratory mucosa. In few cases, it can be possible to detech the presence of cholesterolgranuloma. We present the case of a 55 year-old patient affected by a nasal lesion, localized in sphenoethmoidal recess, with particular microscopic feature and a review of 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

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

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

Development and Characterisation of Aluminium Matrix Nanocomposites AlSi10Mg/MgAl2O4 by Laser Powder Bed Fusion

Recently, additive manufacturing techniques have been gaining attention for the fabrication of parts from aluminium alloys to composites. In this work, the processing of an AlSi10Mg based composite reinforced with 0.5% in weight of MgAl2O4 nanoparticles through laser powder bed fusion (LPBF) process is presented. After an initial investigation about the effect of process parameters on the densification levels, the LPBF materials were analysed in terms of microstructure, thermo-mechanical and mechanical properties. The presence of MgAl2O4 nanoparticles involves an increment of the volumetric energy density delivered to the materials, in order to fabricate samples with high densification levels similar to the AlSi10Mg samples. However, the application of different building parameters results in modifying the size of the cellular structures influencing the mechanical properties and therefore, limiting the strengthening effect of the reinforcement

An investigation on the effect of different multi-step heat treatments on the microstructure, texture and mechanical properties of the DED-produced Ti-6Al-4V alloy

This work deals with the effect of different heat treatments on directed energy deposition (DED)-produced Ti- 6Al-4V samples. Annealing treatments at 1050 ◦C followed by different cooling rates were conducted to allow a complete recrystallization of the microstructure and remove the columnar prior-β grains, thus increasing the overall isotropy of the material. An agine treatment at 540 ◦ C was also performed for further microstructural stabilization. The microstructures, textures and mechanical properties were then assessed. Due to the heat treatments, greatly differing microstructures were achieved in an equiaxed grain morphology. However, a “grain memory” effect was detected which resulted in the grains size increasing along the height of the samples. This effect was correlated to the intrinsic prior-β grain width variation along Z on the as-printed specimens, typical of the DED technology. Electron backscatter diffraction analyses proved that the intensity of the preferential di- rections increased after the heat treatments, likely due to the crystallographic variant selection mechanisms taking place when the samples cool down from the annealing temperature. This effect is also influenced by the significant difference in terms of prior-β grains sizes between the heat-treated and the as-printed specimens. To sum up, a complete homogenization of the material via heat treatment above the β-transus temperature proved to be challenging. In fact, the data suggest that the intrinsic texture-related anisotropy granted by the manufacturing process is very difficult to be eliminated

Low-Power Laser Powder Bed Fusion Processing of Scalmalloy®

Among recently developed high-strength and lightweight alloys, the high-performance Scalmalloy(®) certainly stands out for laser powder bed fusion (LPBF) production. The primary goal of this study was to optimize the Scalmalloy(®) LPBF process parameters by setting power values suitable for the use of lab-scale machines. Despite that these LPBF machines are commonly characterized by considerably lower maximum power values (around 100 W) compared to industrial-scale machines (up to 480 W), they are widely used when quick setup and short processing time are needed and a limited amount of powder is available. In order to obtain the optimal process parameters, the influence of volumetric energy density (VED) on the sample porosity, microstructure and mechanical properties was accurately studied. The obtained results reveal the stability of the microstructural and mechanical behaviour of the alloy for VEDs higher than 175 Jmm(−3). In this way, an energy-and-time-saving choice at low VEDs can be taken for the LPBF production of Scalmalloy(®). After identifying the low-power optimized process parameters, the effects of the heat treatment on the microstructural and mechanical properties were investigated. The results prove that low-VED heat-treated samples produced with an LPBF lab-scale machine can achieve outstanding mechanical performance compared with the results of energy-intensive industrial production