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1. Fabrication of Cu-CNT Composite and Cu Using Laser Powder Bed Fusion Additive Manufacturing

   https://doi.org/10.3390/powders1040014  

   Ladani, Leila; Razmi, Jafar; Sadeghilaridjani, Maryam (December 2022, Powders)

   Additive manufacturing (AM) as a disruptive technique has offered great potential to design and fabricate many metallic components for aerospace, medical, nuclear, and energy applications where parts have complex geometry. However, a limited number of materials suitable for the AM process is one of the shortcomings of this technique, in particular laser AM of copper (Cu) is challenging due to its high thermal conductivity and optical reflectivity, which requires higher heat input to melt powders. Fabrication of composites using AM is also very challenging and not easily achievable using the current powder bed technologies. Here, the feasibility to fabricate pure copper and copper-carbon nanotube (Cu-CNT) composites was investigated using laser powder bed fusion additive manufacturing (LPBF-AM), and 10 × 10 × 10 mm3 cubes of Cu and Cu-CNTs were made by applying a Design of Experiment (DoE) varying three parameters: laser power, laser speed, and hatch spacing at three levels. For both Cu and Cu-CNT samples, relative density above 90% and 80% were achieved, respectively. Density measurement was carried out three times for each sample, and the error was found to be less than 0.1%. Roughness measurement was performed on a 5 mm length of the sample to obtain statistically significant results. As-built Cu showed average surface roughness (Ra) below 20 µm; however, the surface of AM Cu-CNT samples showed roughness values as large as 1 mm. Due to its porous structure, the as-built Cu showed thermal conductivity of ~108 W/m·K and electrical conductivity of ~20% IACS (International Annealed Copper Standard) at room temperature, ~70% and ~80% lower than those of conventionally fabricated bulk Cu. Thermal conductivity and electrical conductivity were ~85 W/m·K and ~10% IACS for as-built Cu-CNT composites at room temperature. As-built Cu-CNTs showed higher thermal conductivity as compared to as-built Cu at a temperature range from 373 K to 873 K. Because of their large surface area, light weight, and large energy absorbing behavior, porous Cu and Cu-CNT materials can be used in electrodes, catalysts and their carriers, capacitors, heat exchangers, and heat and impact absorption. 

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2. Design Rules and In-Situ Quality Monitoring of Thin-Wall Features Made Using Laser Powder Bed Fusion

   https://doi.org/10.1115/MSEC2019-3035  

   Gaikwad, Aniruddha; Imani, Farhad; Rao, Prahalad; Yang, Hui; Reutzel, Edward (June 2019, ASME, Manufacturing Science and Engineering Conference)

   The goal of this work is to quantify the link between the design features (geometry), in-situ process sensor signatures, and build quality of parts made using laser powder bed fusion (LPBF) additive manufacturing (AM) process. This knowledge is critical for establishing design rules for AM parts, and to detecting impending build failures using in-process sensor data. As a step towards this goal, the objectives of this work are two-fold: Quantify the effect of the geometry and orientation on the build quality of thin-wall features. To explain further, the geometry-related factor is the ratio of the length of a thin-wall (l) to its thickness (t) defined as the aspect ratio (length-to-thickness ratio, l/t), and the angular orientation (θ) of the part, which is defined as the angle of the part in the X-Y plane relative to the re-coater blade of the LPBF machine. Assess the thin-wall build quality by analyzing images of the part obtained at each layer from an in-situ optical camera using a convolutional neural network. To realize these objectives, we designed a test part with a set of thin-wall features (fins) with varying aspect ratio from Titanium alloy (Ti-6Al-4V) material — the aspect ratio l/t of the thin-walls ranges from 36 to 183 (11 mm long (constant), and 0.06 mm to 0.3 mm in thickness). These thin-wall test parts were built under three angular orientations of 0°, 60°, and 90°. Further, the parts were examined offline using X-ray computed tomography (XCT). Through the offline XCT data, the build quality of the thin-wall features in terms of their geometric integrity is quantified as a function of the aspect ratio and orientation angle, which suggests a set of design guidelines for building thin-wall structures with LPBF. To monitor the quality of the thin-wall, in-process images of the top surface of the powder bed were acquired at each layer during the build process. The optical images are correlated with the post build quantitative measurements of the thin-wall through a deep learning convolutional neural network (CNN). The statistical correlation (Pearson coefficient, ρ) between the offline XCT measured thin-wall quality, and CNN predicted measurement ranges from 80% to 98%. Consequently, the impending poor quality of a thin-wall is captured from in-situ process data. 

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3. A Numerical Study on the Keyhole Formation During Laser Powder Bed Fusion Process

   https://doi.org/10.1115/1.4044100  

   Shrestha, Subin; Kevin Chou, Y. (October 2019, Journal of Manufacturing Science and Engineering)

   The dynamic phenomenon of a melt pool during the laser powder bed fusion (LPBF) process is complex and sensitive to process parameters. As the energy density input exceeds a certain threshold, a huge vapor depression may form, known as the keyhole. This study focuses on understanding the keyhole behavior and related pore formation during the LPBF process through numerical analysis. For this purpose, a thermo-fluid model with discrete powder particles is developed. The powder distribution, obtained from a discrete element method (DEM), is incorporated into the computational domain to develop a 3D process physics model using flow-3d. The melt pool formation during the conduction mode and the keyhole mode of melting has been discerned and explained. The high energy density leads to the formation of a vapor column and consequently pores under the laser scan track. Further, the keyhole shape resulted from different laser powers and scan speeds is investigated. The numerical results indicated that the keyhole size increases with the increase in the laser power even with the same energy density. The keyhole becomes stable at a higher power, which may reduce the occurrence of pores during laser scanning. 

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4. Assessment of Kerogen Wettability from Contact Angle Goniometry

   https://doi.org/10.1021/acs.energyfuels.3c03175  

   Suekuni, Murilo T; Ezazi, Mohammadamin; Kwon, Gibum; Craddock, Paul R; Allgeier, Alan M (January 2024, Energy & Fuels)

   Understanding the wetting properties of shale reservoirs can benefit their development for energy-related purposes and their potential for long-term carbon dioxide injection and storage. Given its potential volumetric abundance and high surface area, the wetting behavior of kerogen in shale requires assessment. Despite their known limitations, wettability studies are commonly limited to static contact angle (θ) measurements. In this Article, the conflicting factors related to the analysis and interpretation of kerogen wetting via static contact angle measurements are discussed. Contact angle data for deionized water, brine (5% NaCl), and n-dodecane are presented for seven paleomarine type-II kerogens spanning a wide range of thermal maturities (vitrinite reflectance, Ro: 0.55 to 2.75%) and chemical composition (aromatic carbon content, H/C ratio, O/C ratio). Droplets of n-dodecane instantaneously absorbed (θ* ≈ 0°) upon contact with all kerogen pellet surfaces, showing the oleophilic nature of kerogen for all maturities tested. Apparent contact angles of water with kerogen surfaces were positively correlated with H/C ratios and inversely correlated with aromatic carbon content, while the bulk and surface oxygen concentrations did not strongly correlate with the measured data. Kerogen exhibited hydrophobic (θwater > 90°) behavior, except at the highest thermal maturities. For example, the least thermally mature and most thermally mature samples studied presented apparent contact angles for water of 123 ± 15 and 59 ± 10°, respectively. Profilometry analyses showed roughness average values ranging from 0.4 ± 0.1 to 3.9 ± 0.7 μm, with the indication that sample topology can affect measured contact angles, albeit in second order as compared to sample chemistry in this study. We recommend caution when associating contact angle data alone with wetting behavior, as data obtained through sessile droplet analysis are subject to known but not always considered, caveats. 

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5. Process-dependent anisotropic thermal conductivity of laser powder bed fusion AlSi10Mg: impact of microstructure and aluminum-silicon interfaces

   https://doi.org/10.1108/RPJ-09-2022-0290  

   Azizi, Arad; Hejripour, Fatemeh; Goodman, Jacob A.; Kulkarni, Piyush A.; Chen, Xiaobo; Zhou, Guangwen; Schiffres, Scott N. (February 2023, Rapid Prototyping Journal)

   Purpose AlSi10Mg alloy is commonly used in laser powder bed fusion due to its printability, relatively high thermal conductivity, low density and good mechanical properties. However, the thermal conductivity of as-built materials as a function of processing (energy density, laser power, laser scanning speed, support structure) and build orientation, are not well explored in the literature. This study aims to elucidate the relationship between processing, microstructure, and thermal conductivity. Design/methodology/approach The thermal conductivity of laser powder bed fusion (L-PBF) AlSi10Mg samples are investigated by the flash diffusivity and frequency domain thermoreflectance (FDTR) techniques. Thermal conductivities are linked to the microstructure of L-PBF AlSi10Mg, which changes with processing conditions. The through-plane exceeded the in-plane thermal conductivity for all energy densities. A co-located thermal conductivity map by frequency domain thermoreflectance (FDTR) and crystallographic grain orientation map by electron backscattered diffraction (EBSD) was used to investigate the effect of microstructure on thermal conductivity. Findings The highest through-plane thermal conductivity (136 ± 2 W/m-K) was achieved at 59 J/mm 3 and exceeded the values reported previously. The in-plane thermal conductivity peaked at 117 ± 2 W/m-K at 50 J/mm 3 . The trend of thermal conductivity reducing with energy density at similar porosity was primarily due to the reduced grain size producing more Al-Si interfaces that pose thermal resistance. At these interfaces, thermal energy must convert from electrons in the aluminum to phonons in the silicon. The co-located thermal conductivity and crystallographic grain orientation maps confirmed that larger colonies of columnar grains have higher thermal conductivity compared to smaller columnar grains. Practical implications The thermal properties of AlSi10Mg are crucial to heat transfer applications including additively manufactured heatsinks, cold plates, vapor chambers, heat pipes, enclosures and heat exchangers. Additionally, thermal-based nondestructive testing methods require these properties for applications such as defect detection and simulation of L-PBF processes. Industrial standards for L-PBF processes and components can use the data for thermal applications. Originality/value To the best of the authors’ knowledge, this paper is the first to make coupled thermal conductivity maps that were matched to microstructure for L-PBF AlSi10Mg aluminum alloy. This was achieved by a unique in-house thermal conductivity mapping setup and relating the data to local SEM EBSD maps. This provides the first conclusive proof that larger grain sizes can achieve higher thermal conductivity for this processing method and material system. This study also shows that control of the solidification can result in higher thermal conductivity. It was also the first to find that the build substrate (with or without support) has a large effect on thermal conductivity. 

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