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1. Influence of powder type and binder saturation on binder jet 3D–printed and sintered Inconel 625 samples

   https://doi.org/10.1007/s00170-021-07496-3  

   Jiang, Runbo ; Monteil, Lorenzo ; Kimes, Katerina ; Mostafaei, Amir ; Chmielus, Markus ( July 2021 , The International Journal of Advanced Manufacturing Technology)

   null (Ed.)

   Binder jet 3D printing combined with post-deposition sintering is a non-beam additive manufacturing (AM) method for the creation of complex metallic structures. Binder saturation and particle morphology are two important factors affecting the quality of printed parts. Here, we investigated the effects of binder saturation on dimension accuracy, porosity, microstructure and microhardness of nickel-based alloy 625 samples made of differently atomized powders. Argon gas atomized (GA) and water atomized (WA) nickel-based alloy 625 powders were used to binder jet samples for a detailed comparative study. The optimal binder saturation for WA system is 60% to 70%, whereas for GA system the optimal is about 80%. Generally, GA samples achieved better overall quality than WA samples in terms of packing density, dimensional accuracy, sintered density, and microhardness. This difference is attributed mainly to the particle morphology including sphericity and roundness. The critical threshold for visible binder bleeding phenomenon in WA and GA systems is determined to be 120% and 140% binder saturation, respectively. Mechanisms for binder bleeding phenomenon at different saturation levels for WA and GA systems are discussed in detail. A pore evolution model is proposed to better understand the printing and sintering processes. 

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2. Forming mechanism of equilibrium and non-equilibrium metallurgical phases in dissimilar aluminum/steel (Al–Fe) joints

   https://doi.org/10.1038/s41598-021-03578-0  

   Shang, Shun-Li ; Sun, Hui ; Pan, Bo ; Wang, Yi ; Krajewski, Adam M. ; Banu, Mihaela ; Li, Jingjing ; Liu, Zi-Kui ( December 2021 , Scientific Reports)

   Forming metallurgical phases has a critical impact on the performance of dissimilar materials joints. Here, we shed light on the forming mechanism of equilibrium and non-equilibrium intermetallic compounds (IMCs) in dissimilar aluminum/steel joints with respect to processing history (e.g., the pressure and temperature profiles) and chemical composition, where the knowledge of free energy and atomic diffusion in the Al–Fe system was taken from first-principles phonon calculations and data available in the literature. We found that the metastable and ductile (judged by the presently predicted elastic constants) Al₆Fe is a pressure (P) favored IMC observed in processes involving high pressures. The MoSi₂-type Al₂Fe is brittle and a strongP-favored IMC observed at high pressures. The stable, brittle η-Al₅Fe₂is the most observed IMC (followed by θ-Al₁₃Fe₄) in almost all processes, such as fusion/solid-state welding and additive manufacturing (AM), since η-Al₅Fe₂is temperature-favored, possessing high thermodynamic driving force of formation and the fastest atomic diffusivity among all Al–Fe IMCs. Notably, the ductile AlFe₃, the less ductile AlFe, and most of the other IMCs can be formed during AM, making AM a superior process to achieve desired IMCs in dissimilar materials. In addition, the unknown configurations of Al₂Fe and Al₅Fe₂were also examined by machine learning based datamining together with first-principles verifications and structure predictions. All the IMCs that are notP-favored can be identified using the conventional equilibrium phase diagram and the Scheil-Gulliver non-equilibrium simulations.

    

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3. Surface Finishing and Electroless Nickel Plating of Additively Manufactured (AM) Metal Components

   https://doi.org/10.1115/IMECE2021-71882  

   Demisse, Wondwosen ; Mutunga, Eva ; Klein, Kate ; Rice, Lucas ; Tyagi, Pawan ( November 2021 , Conference: Proceedings of the ASME 2021 International Mechanical Engineering Congress and Exposition IMECE2021 November 1-5, 2021, Virtual, Online)

   This study investigates the application of electroless nickel deposition on additively manufactured stainless steel samples. Current additive manufacturing (AM) technologies produce metal components with a rough surface. Rough surfaces generally exhibit fatigue characteristics, increasing the probability of initiating a crack or fracture to the printed part. For this reason, the direct use of as-produced parts in a finished product cannot be actualized, which presents a challenge. Post-processing of the AM parts is therefore required to smoothen the surface. This study analyzes chempolish (CP) and electropolish (EP) surface finishing techniques for post-processing AM stainless steel components CP has a great advantage in creating uniform, smooth surfaces regardless of size or part geometry EP creates an extremely smooth surface, which reduces the surface roughness to the sub-micrometer level.

   In this study, we also investigate nickel deposition on EP, CP, and as-built AM components using electroless nickel solutions. Electroless nickel plating is a method of alloy treatment designed to increase manufactured component’s hardness and surface resistance to the unrelenting environment. The electroless nickel plating process is more straightforward than its counterpart electroplating. We use low-phosphorus (2–5% P), medium-phosphorus (6–9% P), and high-phosphorus (10–13% P). These Ni deposition experiments were optimized using the L9 Taguchi design of experiments (TDOE), which compromises the prosperous content in the solution, surface finish, plane of the geometry, and bath temperature. The pre- and post-processed surface of the AM parts was characterized by KEYENCE Digital MicroscopeVHX-7000 and Phenom XL Desktop SEM. The experimental results show that electroless nickel deposition produces uniform Ni coating on the additively manufactured components up to 20 μm per hour. Mechanical properties of as-built and Ni coated AM samples were analyzed by applying a standard 10 N scratch test. Nickel coated AM samples were up to two times scratch resistant compared to the as-built samples. This study suggests electroless nickel plating is a robust viable option for surface hardening and finishing AM components for various applications and operating conditions. 

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4. Machine-Learning-Based Thermal Conductivity Prediction for Additively Manufactured Alloys

   https://doi.org/10.3390/jmmp7050160  

   Bhandari, Uttam ; Chen, Yehong ; Ding, Huan ; Zeng, Congyuan ; Emanet, Selami ; Gradl, Paul R. ; Guo, Shengmin ( October 2023 , Journal of Manufacturing and Materials Processing)

   Thermal conductivity (TC) is greatly influenced by the working temperature, microstructures, thermal processing (heat treatment) history and the composition of alloys. Due to computational costs and lengthy experimental procedures, obtaining the thermal conductivity for novel alloys, particularly parts made with additive manufacturing, is difficult and it is almost impossible to optimize the compositional space for an absolute targeted value of thermal conductivity. To address these difficulties, a machine learning method is explored to predict the TC of additive manufactured alloys. To accomplish this, an extensive thermal conductivity dataset for additively manufactured alloys was generated for several AM alloy families (nickel, copper, iron, cobalt-based) over various temperatures (300–1273 K). This unique dataset was used in training and validating machine learning models. Among the five different regression machine learning models trained with the dataset, extreme gradient boosting performs the best as compared with other models with an R2 score of 0.99. Furthermore, the accuracy of this model was tested using Inconel 718 and GRCop-42 fabricated with laser powder bed fusion-based additive manufacture, which have never been observed by the extreme gradient boosting model, and a good match between the experimental results and machine learning prediction was observed. The average mean error in predicting the thermal conductivity of Inconel 718 and GRCop-42 at different temperatures was 3.9% and 2.08%, respectively. This paper demonstrates that the thermal conductivity of novel AM alloys could be predicted quickly based on the dataset and the ML model.

    

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5. Hydrolysis protection and sintering of aluminum nitride powders with yttria nanofilms

   https://doi.org/10.1111/jace.18310  

   O'Toole, Rebecca J. ; Hill, Chanel ; Buur, Peter J. ; Bartel, Christopher J. ; Gump, Christopher J. ; Musgrave, Charles B. ; Weimer, Alan W. ( January 2022 , Journal of the American Ceramic Society)

   Aluminum nitride (AlN) is a promising material for electronic substrates and heat sinks. However, AlN powders react with water that adversely affects final part properties and necessitates processing in organic solvents, increasing the cost of AlN parts. Small quantities of yttrium oxide (Y₂O₃) are commonly added to AlN particles to enable liquid phase sintering. To mitigate the reaction of AlN particles with water, particle atomic layer deposition (ALD) was used to coat AlN powders with conformal films of Y₂O₃prior to densification and powder processing. When AlN particles were coated with 6 nm thick films of amorphous Y₂O₃, the hydrolysis reaction was significantly suppressed over 48 h, demonstrating that Y₂O₃nanofilms on AlN powders act as a barrier coating in an aqueous solution. AlN powders with Y₂O₃addition by particle ALD sintered to high relative densities (≥90% theoretical) after sintering at 1800°C for 50 min.

    

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