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Microstructural and Mechanical Properties of Metal ALM
Published in Linkan Bian, Nima Shamsaei, John M. Usher, Laser-Based Additive Manufacturing of Metal Parts, 2017
Moataz M. Attallah, Luke N. Carter, Chunlei Qiu, Noriko Read, Wei Wang
The round pores with smooth walls are generally believed to be gas porosity, which is formed at the end of the solidification. Gas porosity can be divided into the common gas porosity induced by dissolved and trapped gas (e.g., hydrogen-induced porosity in Al-alloys) and keyhole porosity induced by the vaporization of material, as shown in Figure 3.42 [51]. Gas porosity is formed as a result of the dissolved gas being rejected at the liquid–solid interface. The gas pores are also visible in Figure 3.41, and are smaller than 10 μm. The possible sources of the enclosed gas porosity may come from three types. First, they can be hydrogen-induced porosity, with the hydrogen coming from the moisture absorbed in surface of the powder particles and the ambient atmosphere. Second, they can also form from the residual gas pores in the gas atomized powder. Finally, they can be related to keyhole porosity. Keyhole pores can be found at the end of the laser scan track. The principle of laser beam–induced keyhole formation is shown in Figure 3.42. When a laser beam
Heterogeneous sensor data fusion for multiscale, shape agnostic flaw detection in laser powder bed fusion additive manufacturing
Published in Virtual and Physical Prototyping, 2023
Benjamin Bevans, Christopher Barrett, Thomas Spears, Aniruddha Gaikwad, Alex Riensche, Ziyad Smoqi, Harold (Scott) Halliday, Prahalada Rao
There are six primary mechanisms in which porosity, a primary focus of this work, is formed. These are: (i) incomplete melting of the material due to inadequate energy inputted by the laser, called lack-of-fusion porosity. Such pores are acicular and manifest a jagged irregular shape and typically exceed 50 µm in diameter. (ii) Vaporisation of material, and gasses, dissolved in the meltpool to create gas porosity, or pinhole porosity. Such pores are circular in shape and rarely exceed 30 µm in diameter. (iii) Excessive inputted energy by the laser that causes the laser to operate in the keyhole penetration mode. Such keyhole pores form deep within the meltpool and is roughly circular with a diameter less than 50 µm. (iv) Ejected spatter and debris interfering with the laser melting the material and the subsequent solidification. (v) Machine-related flaws, such as soot agglomeration on the f-θ lens of the machine affecting the amount of inputted energy. (vi) Any form of contaminants in the powder material that will interfere with the melting and solidification process of the powder (Gaikwad et al. 2022; Liu and Wen 2022; Montazeri et al. 2018; Mostafaei et al. 2022; Nassar et al. 2019; Snow, Nassar, and Reutzel 2020; Yakout et al. 2021).
Study on fluid mobility in sandwich-type shale oil reservoir using two-dimensional nuclear magnetic resonance approaches
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Rui Shen, Wei Xiong, Hang Yang, Xu Zeng, Guodong Wang, Guoyong Shao
Table 1 and Figure 2 show that silty and fine sandstones were the main types of oil-rich and oil-soaked level lithologies. Therefore, we selected 16 samples of silty and fine sandstones with different porosity and permeability levels in the test. The specific testing steps are as follows: we removed oil from the core samples and then dried them. We tested their gas porosity and permeability. We vacuumized and then saturated the samples with brine. We calculated porosity using the difference between wet and dry weights. And conducted an NMR T2 test on the water-saturated core samples. We subjected the core samples to centrifugal forces of 40 psi, 200 psi, and 400 psi per unit cross-sectional area. We conducted an NMR T2 test on the core samples every time they were centrifuged.
Hierarchical spatial-temporal modeling and monitoring of melt pool evolution in laser-based additive manufacturing
Published in IISE Transactions, 2020
Shenghan Guo, Weihong “Grace’’ Guo, Linkan Bain
An imperative issue hindering a wide application of Laser-Based Additive Manufacturing (LBAM) is the unstable product quality (Khanzadeh, Tian, et al., 2018). According to the literature (Taheri et al., 2017), defects in a finished part include several major types: (i) porosity (gas porosity and porosity due to lack of fusion); (ii) anisotropy and compromised phase stability; (iii) geometrical anomalies, e.g., dimensional inaccuracy, curling, waviness and surface roughness; (iv) balling phenomenon; and (v) cracks. The occurrence of defects results in poor mechanical properties when the loading reaches a certain level. Fatigue cracks are likely to happen due to stress concentrations related to pores and lack-of-fusion defects. It has been shown that as low as 1 vol.% of defect occurrence already has a significant impact on mechanical properties, especially tensile and fatigue life. Elimination of these defects is crucial to an elongated fatigue life of Additive Manufacturing (AM) parts (Taheri et al., 2017). Post-AM processes (including heat treatment and machining) can remove some defects in the finished parts, e.g., surface roughness, dimensional inaccuracy, trivial cracks on the surface. However, such post-AM processing may be expensive – a surging cost is induced by intensive post-AM correction. More importantly, many microstructural anomalies cannot be eliminated in heat treatment or machining, restricting the level of quality improvement (Khanzadeh, Tian, et al., 2018). Therefore, detecting those microstructural defects in real time becomes an urgent need for LBAM applications.