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- 저자 : Bobrowski (검색결과 3 건)
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Effect of Various SPD Techniques on Structure and Superplastic Deformation of Two Phase MgLiAl Alloy
Jan Dutkiewicz,Piotr Bobrowski,Stanislav Rusz,Ondrej Hilser,Tomasz A. Tański,Wojciech Borek,Marek Łagoda,Paweł Ostachowski,Paweł Pałka,Grzegorz Boczkal,Dariusz Kuc,Tomasz Mikuszewski 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.5
MgLiAl alloy containing 9 wt% Li and 1.5% Al composed of hexagonal α and bcc β phases was cast under protecting atmosphereand hot extruded. Various methods of severe plastic deformation were applied to study their effect on structure and grainrefi nement. Rods were subjected to 1–3 passes of Twist Channel Angular Pressing TCAP (with helical component), cycliccompression to total strain ε = 5 using MAXStrain Gleeble equipment, both performed at temperature interval 160–200 °Cand, as third SPD method, KOBO type extrusion at RT. The TCAP pass resulted in grain refi nement of α phase from 30 μmdown to about 2 μm and that of β phase from 12 to 5 μm. Maxstrain cycling 10 × up to ε = 5 led to much fi ner grain size of300 nm. KOBO method performed at RT caused average grain size refi nement of α and β phases down to about 1 μm. Hardnessof alloy decreased slightly with increasing number of TCAP passes due to increase of small void density. It was higherafter MAXStrain cycling and after KOBO extrusion. TEM studies after TCAP passes showed higher dislocation density inthe β region than in the α phase. Crystallographic relationship (001) α|| (110) β indicated parallel positioning of slip planesof both phases. Electron diff raction technique confi rmed increase of grain misorientation with number of TCAP passes. Stress/strain curves recorded at temperature 200 °C showed superplastic forming after 1st and 3rd TCAP passes with bettersuperplastic properties due to higher elongation with increasing number of passes. Values of strain rate sensitivity coeffi cientm were calculated at 0.29 after 3rd TCAP pass for strain rate range 10 −5 to 5 × 10 −3 s −1 . Deformation by MAXStrain cyclingcaused much more effective grain refi nement with fi ne microtwins in α phase. Superplastic deformation was also observed inalloy deformed by KOBO method, however the value of m = 0.21 was obtained at lower temperature of deformation equal to160 °C and deformation rate in the range 10 −5 to 5 × 10 −3 . Tensile samples deformed superplastically showed grain growthand void formation caused by grain boundary slip. Summarizing, all methods applied resulted in suffi cient grain refi nementto obtain the effect of superplastic deformation for alloys of two phase α + β structure.
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Łukasz Rogal,Zbigniew Szklarz,Piotr Bobrowski,Damian Kalita,Grzegorz Garzeł,Anna Tarasek,Marcin Kot,Maciej Szlezynger 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.4
Four diff erent compositions of high entropy alloys based on Al–Co–Cr–Fe and Al–Co–Cr–Fe–Ni systems were preparedusing mechanical alloying and consolidation by spark plasma sintering. The chemical compositions of the studied alloyswere experimentally selected to obtain a BCC solid solution and mixtures of BCC with FCC. The microstructure of theAl25Co25Cr25Fe25 (all in at%) high entropy alloy consisted of a matrix with a high concentration of Al, Co and Fe, in whichspherical grains (50–200 nm) enriched in Cr were embedded. Both the matrix and grains had body centered cubic structures. The addition of nickel to a four-element system led to the formation of a multiphase composition. The microstructure of theAl20Co20Cr20Fe20Ni20, Al10Co30Cr20Fe35Ni5 and Al15Co30Cr15Fe40Ni5 HEAs consisted of fi ne grains measuring50–500 nm composed of: AlNi-B2, BCC phase, FCC or BCC solid solutions and σ-sigma phase, respectively. The complexstructure of the studied samples resulted in changeable mechanical properties. The highest compression strength of 3920 MPawas accompanied by an increased yield strength of 3500 MPa, and a low strain of 0.7%, for the Al25Co25Cr25Fe25 alloy. The addition of Ni led to the formation of plastic FCC phases responsible for a decrease in strength with increases in ductility,which, in the new non-equiatomic Al10Co30Cr20Fe35Ni5 high entropy alloy reached 6.3% at a yield strength of 1890 MPaand compression strength of 2230 MPa. The conducted abrasion studies revealed that non-equilibrium high entropy alloyshave the highest abrasion resistance.
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Acute Toxicity and Cytotoxicity of Pereskia aculeata, a Highly Nutritious Cactaceae Plant
Debora O. Silva,Mauricio Seifert,Fabiana R. Nora,Vera L. Bobrowski,Rogerio A. Freitag,Heidi R. Kucera,Leonardo Nora,Nilesh W. Gaikwad 한국식품영양과학회 2017 Journal of medicinal food Vol.20 No.4
Pereskia aculeata is a Cactaceae plant with valuable nutritional properties, including terrific amounts of protein, minerals, vitamins, and fiber. However, P. aculeata is reported to contain antinutrients and alkaloids in its leaves. In addition, in a study on growth and development, Wistar rats fed with P. aculeata and casein as protein source grew less than the control group (fed with casein only). Therefore, in this study, we evaluated, for the first time, the oral acute toxicity of P. aculeata in rats and also the cytotoxicity behavior of the plant on lettuce seeds. The acute toxicity research was carried out using dried P. aculeata ethanolic extract, in three different doses, administered by gavage to 24 female Wistar rats. The rats were then examined for signs of toxicity, food intake, body weight, and fecal excretion fluctuations, as well as histopathological alterations, using eight different body tissues. The acute toxicity study did not show any difference among the groups in either clinical evaluation or histopathological analyses. For the cytotoxicity study, dried P. aculeata ethanolic extract was applied on lettuce seeds in five different concentrations. These seeds were evaluated for germination, root and shoot length, and mitotic index. The results show that P. aculeata extract affects lettuce root and shoot growth, but not germination or mitotic index. In conclusion, the acute toxicity on rats and the cytogenotoxicity on lettuce of P. aculeata are neglectable, validating the potential of this plant to be used as a functional food.
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