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- Lin, Sen, 1993-, et al.
(författare)
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Effect of Mo addition on bainite formation in steels - A high-energy X-ray diffraction study
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The influence of Mo addition (0, 0.1, 0.4 wt%) on the bainitic transformation in a steel with base composition Fe-0.2C-1.7Mn-0.4Si (in wt%) was studied by means of in-situ high-energy X-ray diffraction (HEXRD) and electron microscopy. The phase evolution of bainitic ferrite, cementite and retained austenite during isothermal heat treatment at 673, 723, and 773 K was quantitatively analyzed. The evolution of the C content in the retained austenite and the dislocation density in the bainitic ferrite were also investigated. The results show that the addition of 0.1 wt% Mo barely affects the transformation kinetics, while the addition of 0.4 wt% Mo leads to a bay in the time-temperature-transformation diagram, possibly due to a solute drag effect. The incomplete transformation occurs at the highest isothermal heat treatment temperature, i.e., 773 K. At the lower isothermal heat treatment temperature 673 K, the bainitic transformation is accelerated by adding 0.4 wt% Mo due to an increased tendency of cementite formation, which decreases the overall C content in retained austenite and C and Mo accumulation at the phase interface, thus reducing the solute drag effect.
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| 2. |
- Lin, Sen, 1993-, et al.
(författare)
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Formation of cementite and transition carbides during bainitic transformation in steels with and without incomplete transformation stage
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The kinetics of carbide precipitation during isothermal bainitic transformation in a Fe-0.448C-1.78Mn-1.20Si (in wt%) steel is investigated using in-situ high-energy X-ray diffraction and electron microscopy. For the sample heat treated at 623 K for 1 h, the bainitic transformation is incomplete and transition carbides are observed. For the sample heat treated at 673 K, the initial formation of bainitic ferrite is accompanied by the formation of transition carbide, and at a later transformation stage, cementite starts to form until the bainitic transformation reaches completion, whereas the amount of transition carbides decreases.
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| 3. |
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| 4. |
- Pérez Caro, Lluís, 1985-, et al.
(författare)
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Shape prediction of a hot formed component in nickel-base superalloys
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Current manufacturing processes of advanced aero engine components in nickel-base superalloys are performed at approximately 950 °C, with varying holding times, to reduce the amount of residual stresses, and thereby shape deviations, over the part. The aim of such procedures is to obtain the final geometry of the component within tolerance and avoid costly tryouts, which can be unfavorable to the competitiveness of the aerospace industry. In addition, a reduction in the forming temperature or holding time may significantly reduce the energy consumption and carbon dioxide (CO2) emissions while increasing the ecological sustainability of the process. In this work, the numerical study of a hot forming procedure of a double-curved component in Haynes® 282® is presented. The influence of the forming temperature and holding time on the predicted amount of springback at different stages of the hot forming procedure is assessed. The resulting shape distortions are compared with identical FE analyses in alloy 718 at 870 °C available in literature. The anisotropic properties of the material are determined at temperatures ranging from 20 to 1000 °C. A qualitative analysis of the different types of serrations present in the hardening curves between 300 and 900 °C is included in the study. Microstructural observations of selected specimens are correlated to the material-characterization tests. The thermo-mechanical data is used as input to the novel version of the Barlat Yld2000-2D material model in LS-DYNA. The results show that forming of Haynes® 282® at 870 °C produces high shape distortions over the part with values beyond the sheet thickness, in contrast to the response of alloy 718. A comparison of the stress-relaxation rate with available data in literature for alloy 718 at 870 °C reveals that Haynes® 282® relaxes about 50% slower than alloy 718, whereas reasonably analogous at 950 °C. An increase in the forming temperature to 950 °C significantly reduces the amount of springback. Therefore, it can be concluded that forming of Haynes® 282® requires a higher temperature than reported for alloy 718 to reach similar amount of springback. The presented studies indicate that the use of advanced anisotropic models together with the thermo-mechanical properties and stress-relaxation behavior of the material is of utmost importance to accurately predict the final geometry of lightweight components of interest to the aerospace industry.
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| 5. |
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| 6. |
- Ali, Sharafat, 1976-
(författare)
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Glass surface modification by aerosol technique
- 2016
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Annan publikation (refereegranskat)abstract
- Glass has been a key material for many important advnces in cilivilization. Currently there is much scientific and technological interest to obtained flat/float glass surface that has extremely highly resistant to abrasion, anti-fingerprint, surface contamination and optical dimming. The aim of current project is to develop new routes to modify the glass surface in order to increase functionality and enhance performance in various existing and future areas of application. This will be achieved by modifying the glass surface by incorporating nitrogen to the flat/float glass surface by deposition of thin coatings of AlN, Si3N4 and TiN. This will be achieved by gas to particle conversion by physiochemical routs. Thin films of elemental nitrides have not been reported previously by aerosol technique and we anticipate that these can be used to enhance the mechanical, optical and chemical properties of flat/float glass surface. Techniques used for structural and physical characterization include, SEM, TEM, AFM, Raman, thermal analysis, mechanical and optical measurements. Areas of applications of these modified surfaces include automotive, architectural, laser optics, camera lenses, optical filters and display technologies.
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| 7. |
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| 8. |
- Chen, Chao, 1986-
(författare)
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Bactericidal Surfaces Prepared by Femtosecond Laser Patterning and Layer-by-Layer Polyelectrolyte Coating
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Antimicrobial surfaces are important in medical, clinical, and industrial applications, where bacterial infection and biofouling may constitute a serious threat to human health. Conventional approaches against bacteria involve coating the surface with antibiotics, cytotoxic polymers, or metal particles. However, these types of functionalization have a limited life-time and pose concerns in terms of leaching and degradation of the coating. Thus, there is a great interest in developing long-lasting and non-leaching bactericidal surfaces. To obtain a bactericidal surface, we combine μm-scale patterning of borosilicate glass surfaces by ultrashort pulsed laser irradiation and a non-leaching layer-by-layer polyelectrolyte modification of the surface. The combination of surface structure and surface charge results in an enhanced bactericidal effect against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. The laser patterning and the layer-by-layer modification are environmentally friendly processes that are applicable to a wide variety of materials, which makes this method uniquely suited for fundamental studies of bacteria-surface interactions and paves the way for its applications in a variety of fields, such as in hygiene products and medical devices.
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| 9. |
- Fondell, Mattis, 1984-, et al.
(författare)
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Phase control of iron oxides grown in nano-scale cauliflower structures: hematite, maghemite and magnetite
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate that iron oxide in the form of hematite, suitable as absorber in photoelectrochemical cells, can be produced by pulsed chemical vapour deposition. By choosing carbon monoxide or nitrogen as carrier gases in the process the phase and granularity of the grown material can be controlled. The choice of carrier gas a ect the decomposition rate of iron pentacarbonyl used as iron precursor. The iron oxide phase is also dependent on the chosen substrate, here fluorine doped tin oxide and crystalline silicon have been used. Regardless of the substrate nitrogen yields hematite, whereas carbon monoxide gives magnetite on Si and maghemite on fluorine doped tin oxide. A combination of Raman spectroscopy, X-ray di raction, and hard X-ray photoelectron spectroscopy were used for characterization of the crystalline phase and chemical composition in the films. Scanning electron microscopy were used to visualise the deposited films’ nano-structure reminiscent of a cauliflower.
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| 10. |
- Heydari, Golrokh, 1982-, et al.
(författare)
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Ultralow ice adhesion on hydrophilic and molecularly smooth mica surfaces
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Despite much research on designing surfaces for combating icing, no permanent solution has been achievedusing solid materials. Inspired by the slippery surface of ice, attributed to the presence of a quasi-liquid layeracting as a natural lubricant, we hypothesize that flat hydrophilic surfaces with a hydration layer remaining inthe liquid-like state at the solid-ice interface could result in low ice adhesion. Utilizing temperature-controlledice adhesion measurements on the molecularly smooth basal plane of muscovite mica, we observed the lowestreported ice adhesion on solid surfaces down to temperatures of -35 ºC. The ice adhesion is dramatically higheron flat hydrophilic silica surfaces. We discuss these findings in terms of what is known about mica-water andmica-ice interactions.
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