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| 2. |
- Chou, Chia-Ying, et al.
(författare)
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Influence of solidification structure on austenite to martensite transformation in additively manufactured hot-work tool steels
- 2021
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of a hot-work tool steel additively manufactured using laser powder-bed fusion (L-PBF), and its response to post heat treatment, is studied in detail by microstructure characterization and computational thermodynamics and kinetics. The high solidification and cooling rates during the L-PBF process lead to suppression of delta-ferrite and instead solidification of an austenite phase directly containing a cellular substructure where the alloying elements have segregated to the inter-cellular regions and where solidification carbides have formed in the cell junctions. The austenite is then partly decomposed into martensite at lower temperatures. The micro-segregation can be predicted by reducing the complex solidification behavior to a diffusion problem in one dimension enabling detailed comparisons with the measured segregation profiles quantified at a nanometer scale. Martensite start temperature (M-s) calculations along the spatially varying composition show that the M-s temperature decreases in the inter-cellular regions where austenite is observed. The network of austenite in the as-built microstructure can be understood from the combined influence of the composition dependence of the M-s temperature in relation to the build plate temperature and the mechanical stabilization of the small-sized austenite regions. This work demonstrates the power of computational tools based on computational thermodynamics and kinetics for designing tool steels for additive manufacturing by predictions of the steel's response to the L-PBF process and post heat treatments.
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| 3. |
- Chou, Chia-Ying, 1990-
(författare)
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Integrated Computational and Experimental Study of Additively Manufactured Steels
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The design freedom Additive Manufacturing (AM) offers provides new solutions for improving functionality in industrial applications. It also offers unique opportunities when it comes to materials design.Powder Bed Fusion – Laser Beam (PBF-LB) is currently one of the most popular commercial AM techniques for metallic materials partly due to the relatively low surface roughness and the large design flexibility. However, the number of materials suitable for the PBF-LB process is still rather low and to accelerate the development of grades tailored for this AM process, dedicated computational tools for alloy design are needed. Of importance for materials design, is computational thermodynamics and kinetics coupled with CALPHAD materials descriptions since it enables calculations for multicomponent materials making it possible to predict the effect of varying composition.In this thesis, computational thermodynamic and kinetics coupled with materials characterization are applied to study the microstructure evolution during PBF-LB. Two material classes are in focus – hot-work tool steels and ferritic stainless steels. For the hot-work tool steel, the cooling rates during PBF-LB processing are high enough to induce martensite transformation and in the as-built microstructure a martensitic matrix is observed and some fraction of retained austenite. A solidification sub-structure due to micro-segregation during printing is also observed. Solidification calculations are performed to predict the micro-segregation showing agreement with experimental measurements. The segregation results are then used as input to a semi-empirical martensite start temperature model making it possible to explain the location and amount of retained austenite.In addition to compositional optimization, a computational framework for AM alloy design needs to include the possibility to tailor the AM post heat treatments. An alternative to the conventional hardening treatment is thus studied in the current work. A model for precipitation kinetics is combined with experimental characterization to explore the effect of tempering on the as-built microstructure in comparison to the tempering effect on an austenitized microstructure. The results show that the precipitation kinetics is strongly dependent on the starting structure and that direct tempering of the as-built microstructure changes the precipitation sequence compared to the conventional heat treatment route. The calculations reproduce this result suggesting that it is a thermodynamic effect stemming from different matrix compositions.The other material class, the ferritic stainless steels, is studied in terms of its response to post-heat treatments. The as-built microstructure is characterized by high dislocation density and a fine grain structure in some cases as well as a solidification sub-structure. The mechanical properties of the as-built material are in general good for these steels, however, stress relieving is most often a required post process for the as-built components which may decrease the mechanical properties. To maximize the gained benefits from the unique process condition of PBF-LB, simulations are applied to study the possibility of post heat treatment optimization.To construct a computational framework for AM materials design, multiscale modeling capabilities are needed. This work shows the value of computational thermodynamics and kinetics for understanding the materials behavior on the microscale and hence, contributes to the construction of such a framework. By understanding the physical metallurgy, and enable modeling of the AM processes, the industrialization of AM can be accelerated.
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| 4. |
- Chou, Chia-Ying, et al.
(författare)
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Precipitation kinetics during post-heat treatment of a L-PBF processed SS446 ferritic stainless steel
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The microstructure response to post-heat treatments of SS446 ferritic stainless steel processed by laser powder bed fusion is investigated, with focus on the precipitation kinetics of Cr2N. Precipitation simulations are conducted using the precipitation module (TC-PRISMA) within the Thermo-Calc Software Package. The annealed microstructure is characterized by scanning electron microscopy and the results are used for model validation and calibration. The microstructure and hardness responses to post heat treatments is discussed in terms of optimal solid-solution strengthening in SS446 ferritic stainless steel alloys processed by laser-powder bed fusion.
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| 6. |
- Chou, Chia-Ying, et al.
(författare)
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Precipitation Kinetics During Post-heat Treatment of an Additively Manufactured Ferritic Stainless Steel
- 2022
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Nature. - 1073-5623 .- 1543-1940. ; 53:8, s. 3073-3082
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure response of laser-powder bed fusion (L-PBF)-processed ferritic stainless steel (AISI 441) during post-heat treatments is studied in detail. Focus is on the precipitation kinetics of the Nb-rich phases: Laves (Fe2Nb) and the cubic carbo-nitride (NbC), as well as the grain structure evolution. The evolution of the precipitates is characterized using scanning and transmission electron microscopy (SEM and TEM) and the experimental results are used to calibrate precipitation kinetics simulations using the precipitation module (TC-PRISMA) within the Thermo-Calc Software package. The calculations reproduce the main trend for both the mean radii for the Laves phase and the NbC, and the amount of Laves phase, as a function of temperature. The calibrated model can be used to optimize the post-heat treatment of additively manufactured ferritic stainless steel components and offer a creator tool for process and structure linkages in an integrated computational materials engineering (ICME) framework for alloy and process development of additively manufactured ferritic steels.
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| 7. |
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| 8. |
- Hua, Kuo-Tai, et al.
(författare)
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N-α-acetyltransferase 10 protein suppresses cancer cell metastasis by binding PIX proteins and inhibiting Cdc42/Rac1 activity
- 2011
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Ingår i: Cancer Cell. - : Cell Press. - 1535-6108 .- 1878-3686. ; 19:2, s. 218-231
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Tidskriftsartikel (refereegranskat)abstract
- N-α-acetyltransferase 10 protein, Naa10p, is an N-acetyltransferase known to be involved in cell cycle control. We found that Naa10p was expressed lower in varieties of malignancies with lymph node metastasis compared with non-lymph node metastasis. Higher Naa10p expression correlates the survival of lung cancer patients. Naa10p significantly suppressed migration, tumor growth, and metastasis independent of its enzymatic activity. Instead, Naa10p binds to the GIT-binding domain of PIX, thereby preventing the formation of the GIT-PIX-Paxillin complex, resulting in reduced intrinsic Cdc42/Rac1 activity and decreased cell migration. Forced expression of PIX in Naa10-transfected tumor cells restored the migration and metastasis ability. We suggest that Naa10p functions as a tumor metastasis suppressor by disrupting the migratory complex, PIX-GIT- Paxillin, in cancer cells.
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| 9. |
- Karlsson, Dennis, et al.
(författare)
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Additive manufacturing of the ferritic stainless steel SS441
- 2020
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Ingår i: Additive Manufacturing. - AMSTERDAM, NETHERLANDS : Elsevier BV. - 2214-8604 .- 2214-7810. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the ferritic stainless steel SS441 was produced with excellent mechanical properties using laser powder bed fusion (L-PBF) compared to samples produced by conventional casting and hot-rolling. In addition, thermodynamic calculations were utilized to study the phase stability at elevated temperatures and to understand the solidification behavior. The hot-rolled sample showed a grain size up to several hundred mu m with additional precipitates of TiN and Nb(C,N). In contrast, the as-built L-PBF samples displayed a grain size in the mu m range. Spherical precipitates with a size of around 50 nm could be observed and were attributed to a corundum phase from the thermodynamic calculations. The printed material shows superior mechanical properties, with more than 30 times higher impact energy compared to the hot-rolled alloy (217 +/- 5 J vs. 7 +/- 0.5 J). Furthermore, the properties are anisotropic for the L-PBF produced alloy, with the highest tensile strength vertical to the build direction. The superior mechanical properties of the L-PBF produced sample can be attributed to a smaller grain size, giving a higher strength according to the Hall-Petch relationship. The anisotropy of the material can be eliminated by heat treatments at 900 degrees C followed by water quenching, but the absolute strength decreases slightly due to formation of intermetallic phases such as Nb(C,N) and the Fe2Nb Laves phase. The results clearly illustrates that L-PBF provides a promising manufacturing mute for enhanced strength of ferritic stainless steels.
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| 10. |
- Lai, Kuei-Hung, et al.
(författare)
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Antileukemic Scalarane Sesterterpenoids and Meroditerpenoid from Carteriospongia (Phyllospongia) sp., Induce Apoptosis via Dual Inhibitory Effects on Topoisomerase II and Hsp90
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Two new scalarane sesterterpenoids, 12 beta-(3'beta-hydroxybutanoyloxy)-20,24-dimethyl-24-oxo-scalara-16-en-25-al (1) and 12 beta-(3'beta-hydroxypentanoyloxy)-20,24-dimethyl-24-oxo-scalara-16-en-25-al (2), along with one known tetraprenyltoluquinol-related metabolite (3), were isolated from the sponge Carteriospongia sp. In leukemia Molt 4 cells, 1 at 0.0625 mu g/mL (125 nM) triggered mitochondrial membrane potential (MMP) disruption and apoptosis showing more potent effect than 2 and 3. The isolates inhibited topoisomerase II alpha expression. The apoptotic-inducing effect of 3 was supported by the in vivo experiment through suppressing the volume of xenograft tumor growth (47.58%) compared with the control. Compound 1 apoptotic mechanism of action in Molt 4 cells was further elucidated through inducing ROS generation, calcium release and ER stress. Using the molecular docking analysis, 1 exhibited more binding affinity to N-terminal ATP-binding pocket of Hsp90 protein than 17-AAG, a standard Hsp90 inhibitor. The expression of Hsp90 client proteins, Akt, p70(S6k), NF kappa B, Raf-1, p-GSK3 beta, and XIAP, MDM 2 and Rb2, and CDK4 and Cyclin D3, HIF1 and HSF1 were suppressed by the use of 1. However, the expression of Hsp70, acetylated tubulin, and activated caspase 3 were induced after 1 treatment. Our results suggested that the proapoptotic effect of the isolates is mediated through the inhibition of Hsp90 and topoisomerase activities.
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