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Bandar AlMangour,Jinquan Cheng,Dariusz Grzesiak,Yu‑Jin Hwang,Kee‑Ahn Lee 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.2
The low density and high biocompatibility of Mg-based materials make them suitable for lightweight structural and biomedicalapplications. In this study, we explored the use of selective laser melting (SLM)–an additive manufacturing processwherein metal powders are consolidated in a layer-by-layer manner, allowing the fabrication of complex components. SLMtypically involves complex physicochemical phenomena and results in laser-processing defects, which makes it difficult topredict the densification mechanisms of the melt pool. Therefore, a full-scale model was developed to investigate the thermalbehavior of the melt pool (e.g., temperature gradient distribution, melt pool dimensions, and cooling rate) and the resultantdensification activity under various laser energy density (η) values. In parallel, experimental investigations of the densificationbehavior and microstructural evolution were undertaken with the same SLM processing parameters. The challengesassociated with the SLM processability of Mg were comprehensively addressed. Both the peak temperature gradients withinthe molten pool and molten pool dimensions increased with increasing η, and an opposite trend was observed for the coolingrate. A low η (i.e., high scanning speed) results in a low operating temperature and short liquid lifetime, which in turn leadto poor wettability and many pore-chain and balling defects. However, high η values generated melt pool instability, whichresulted in extensive evaporation, cracks, and porosity. The SLM-processed samples had fine twin-like microstructures asa result of rapid solidification. The experimental and simulation results agreed well, validating the thermal behavior of themolten pool and underlying physical mechanism.
Kim, Young-Kyun,Park, Soon-Hong,Yu, Ji-Hun,AlMangour, Bandar,Lee, Kee-Ahn Elsevier 2018 Materials science & engineering. properties, micro Vol.715 No.-
<P><B>Abstract</B></P> <P>This study seeks to control the microstructure of Ti-6Al-4V alloy produced by a selective laser melting process using only heat treatment, while also improving the high temperature creep behavior. Initial microstructure observation showed a fully martensite structure for the as-fabricated specimen and a fine widmanstätten structure for the heat-treated specimen. Hardness tests indicated that the hardness of the material decreased somewhat, but the anisotropy of the mechanical properties (common in additive manufactured materials) disappeared. Compression tests at 500°C indicated that the yield strength of the as-fabricated specimen was approximately 930MPa, while in the heat-treated specimen it was approximately 557MPa. High temperature compressive creep tests showed that the heat-treated specimen had relatively low creep strain and low steady-state creep rate (superior creep resistance) in all stress ranges, which is the opposite of the compressive yield strength results. After creep deformation, the microstructural evolution of the as-fabricated and heat-treated specimens was compared, and the microstructure changed much more extensively in the as-fabricated specimen. Correlations between microstructures, hardness, strength and creep properties were discussed based on these results.</P>
Kang, Yeon-Ji,Yang, Sangsun,Kim, Young-Kyun,AlMangour, Bandar,Lee, Kee-Ahn Elsevier 2019 Corrosion science Vol.158 No.-
<P><B>Abstract</B></P> <P>The effect of solution ageing and hot isostatic pressing treatments on the high-temperature (900, 1000 °C) oxidation of selective laser melted Inconel 718 alloy was studied. Oxidation results showed improved oxidation resistance after HIP treatment, attributed to higher density of the HIP sample and microstructural differences at the grain boundaries. Cations diffused along the grain boundary in SA alloy, while Ti-rich carbides retarded grain boundary diffusion in HIPed alloy. In SA alloy, the γ” and <I>δ</I> phases were observed within the grain, and at the molten pool boundary, respectively. In HIPed alloy, discontinuous MC were observed, along with fine γ’ phases.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Post-treatment processing of additively manufactured Inconel 718 alloy were investigated </LI> <LI> Hot isostatic pressing enhanced corrosion protection compared to solution ageing. </LI> <LI> Different grain boundary microstructures were developed during post-treatments </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>