| 1. |
- Babu, Prasath, et al.
(författare)
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On the formation and stability of precipitate phases in a near lamellar γ-TiAl based alloy during creep
- 2018
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Ingår i: Intermetallics (Barking). - : Elsevier. - 0966-9795 .- 1879-0216. ; 98, s. 115-125
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Tidskriftsartikel (refereegranskat)abstract
- The formation, evolution and stability of metastable phases observed in the γ-TiAl based alloy Ti-47Al-2Cr-2Nb was studied under creep deformation with stress applied at two different hard orientations in a highly textured as-cast + HIPed material. Previously we have reported that the metastable phase Ti(Al,Cr)2 with C14 Laves phase structure forms at the γ-α2 interface which acts as sink for the alloying elements ejected from the dissolving α2 phase and also expected to effectively control the interface stresses through short range diffusion and modifications in the chemical composition [1]. Ab initio density functional theory based calculations were carried out to evaluate the effect of choice of lattice position and site occupancy of aluminium atoms in the Ti(Al,Cr)2 structure on the lattice parameter variation and thermodynamic stability. C14 with the composition 25 at. % Al was found to have lattice parameter values close to the inter-planar spacing of <110>γ and <10-10>α2 which would have a lower misfit with C14 across the interface. From the cohesive energy calculations, Laves phase C14 with a constrained lattice parameter due to the adjoining phases, exhibits higher stability than the B2 and L10 structures across a range of compositions studied. Electron diffraction simulations of C14 with a composition of 25% Al compared with the experimental data suggest that the structure C14 has taken up either a random site occupancy compared to a specific choice of ordering to minimize the interfacial stress. Though the experimental evidences do not strongly support a long-range ordering theory in C14, short-range ordering could be a tangible choice for alleviating interface misfits. The ability of C14 to assume different lattice parameters at and far from the α2-γ interface also suggest that the C14 acts as buffer layer between α2 and γ phases in the presence of local stresses, although this is not the thermodynamically expected phase at the temperature of creep experiment.
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| 2. |
- Chaithanya Kumar, K. N., et al.
(författare)
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Effect of Prior Deformation on the Formation of the Martensite Phase in Ti-6Al-4V Alloy
- 2022
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Ingår i: JOM. - : Springer Nature. - 1047-4838 .- 1543-1851. ; 74:11, s. 4081-4093
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Tidskriftsartikel (refereegranskat)abstract
- The effect of prior deformation on the evolution of the martensite phase in Ti-6Al-4V alloy is reported by varying the hot-rolling temperature to have different stored energies. While the morphology of the martensite phase is greatly influenced by the prior deformation, the phase fraction is primarily dependent on the quenching temperature. The compositional deviation from the equilibrium condition, emerging from the differences in the diffusion of elements at different rolling temperatures, govern the nucleation and aspect ratio of the martensite laths. Higher stored energy in the deformed samples, calculated as the dislocation density, is found to derive the formation of a twinned plate martensite. Martensitic transformation, irrespective of the prior deformation condition, induces a strong variant selection based on the minimization of the transformation strain energy. However, a strong correlation between the morphology and the character of the intervariant boundaries of the martensite phase is established. The intervariant boundary distribution in martensite showed three major angle–axis pairs associated with the Burgers orientation relationship. The hardness of the martensite phase is determined by the solid solution strengthening, martensite morphology, and microstrain present in the sample.
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| 3. |
- Chang, Tingru, et al.
(författare)
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Effect of blue light illumination on atmospheric corrosion and bacterial adhesion on copper
- 2024
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- The effect of blue light on atmospheric corrosion of Cu and on the antimicrobial properties was explored upon exposure mimicking the condition of hygienic surface disinfection. The results show that blue light illumination enhanced the formation of Cu2O, resulting in a slightly increased corrosion resistance of Cu without pre-deposited NaCl, whereas the enhanced formation of Cu2O, CuCl and/or Cu(OH)3Cl on copper with pre-deposited NaCl caused concomitant corrosion product flaking and a reduced corrosion resistance. The blue light induced enhancement of Cu corrosion led to increased surface roughness and more pronounced integration of bacteria within the corrosion products.
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| 4. |
- Chang, Tingru, et al.
(författare)
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High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:41, s. 49402-49413
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms of bacterial contact killing induced by Cu surfaces were explored through high-resolution studies based on combinations of the focused ion beam (FIB), scanning transmission electron microscopy (STEM), high-resolution TEM, and nanoscale Fourier transform infrared spectroscopy (nano-FTIR) microscopy of individual bacterial cells of Gram-positive Bacillus subtilis in direct contact with Cu metal and Cu5Zn5Al1Sn surfaces after high-touch corrosion conditions. This approach permitted subcellular information to be extracted from the bioinorganic interface between a single bacterium and Cu/Cu5Zn5Al1Sn surfaces after complete contact killing. Early stages of interaction between individual bacteria and the metal/alloy surfaces include cell leakage of extracellular polymeric substances (EPSs) from the bacterium and changes in the metal/alloy surface composition upon adherence of bacteria. Three key observations responsible for Cu-induced contact killing include cell membrane damage, formation of nanosized copper-containing particles within the bacteria cell, and intracellular copper redox reactions. Direct evidence of cell membrane damage was observed upon contact with both Cu metal and Cu5Zn5Al1Sn surfaces. Cell membrane damage permits copper to enter into the cell interior through two possible routes, as small fragmentized Cu2O particles from the corrosion product layer and/or as released copper ions. This results in the presence of intracellular copper oxide nanoparticles inside the cell. The nanosized particles consist primarily of CuO with smaller amounts of Cu2O. The existence of two oxidation states of copper suggests that intracellular redox reactions play an important role. The nanoparticle formation can be regarded as a detoxification process of copper, which immobilizes copper ions via transformation processes within the bacteria into poorly soluble or even insoluble nanosized Cu structures. Similarly, the formation of primarily Cu(II) oxide nanoparticles could be a possible way for the bacteria to deactivate the toxic effects induced by copper ions via conversion of Cu(I) to Cu(II).
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| 5. |
- Francis, E., et al.
(författare)
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Effect of Nb and Fe on damage evolution in a Zr-alloy during proton and neutron irradiation
- 2019
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 165, s. 603-614
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Tidskriftsartikel (refereegranskat)abstract
- Detailed analysis was carried out on proton and a neutron irradiated Nb-containing Zr-alloy to study the evolution of dislocation loop size and densities as well as the formation and evolution of irradiation induced precipitation/clustering. The results obtained here have been contrasted against previously published work on a Nb-free Zr-alloy [1, 21 to investigate the mechanistic reason for the improved resistance to irradiation-induced growth of Nb-containing Zr alloys. The combined use of bright field scanning transmission electron microscopy, ultra-high-resolution energy dispersive spectroscopy and atom probe tomography analysis provides evidence of evenly distributed radiation-induced Nb dusters that have formed during the early stage of proton irradiation and Fe-rich nano-rods near Fe-containing second phase particles. The former seems to have a profound effect on loop and subsequent loop formation, keeping loop size small but number density high while loops seem to initially form at similar dose levels compared to a Nb-free alloy but loop line density does not increase during further irradiation. It is hypothesized that the formation of the Nb nano-precipitates/clusters significantly hinders mobility and growth of loops, resulting in a small size, high number density and limited ability of loops to arrange along basal traces compared to Nb-free Zr-alloys. It is suggested that it is the limited loop arrangement that slows down loop formation and the root cause for the high resistance of Nb-containing Zr-alloys to irradiation-induced growth.
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| 6. |
- Hoseini-Athar, M. M., et al.
(författare)
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Effect of Zn addition on dynamic recrystallization behavior of Mg-2Gd alloy during high-temperature deformation
- 2019
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Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 806, s. 1200-1206
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Zn/Gd ratio on dynamic recrystallization (DRX) of Mg-2Gd-xZn (x = 0, 1, 2 and 3 wt%) alloys was investigated by shear punch tests in the temperature range of 623-723 K and shear strain rate range of 1.0 x 10(-2)-1.2 x 10(-1) s(-1). It was observed that at low Zn/Gd ratio, excessive co-segregation of Gd and Zn solute atoms retards recrystallization and provides higher strength. At high Zn/Gd ratios, precipitation reduces the co-segregation, so that the alloy with Zn/Gd = 1.5, experienced the fastest DRX and the lowest strength. In addition, segregation resulted in a weaker texture, by elimination of nucleation and growth of the preferred orientations. rights reserved.
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| 7. |
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| 8. |
- Hoseini-Athar, M. M., et al.
(författare)
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Microstructural evolution and superplastic behavior of a fine-grained Mg-Gd alloy processed by constrained groove pressing
- 2019
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Ingår i: Materials Science & Engineering. - : ELSEVIER SCIENCE SA. - 0921-5093 .- 1873-4936. ; 754, s. 390-399
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Tidskriftsartikel (refereegranskat)abstract
- In the current study, microstructural evolution and superplasticity of an extruded Mg-2wt% Gd sheet were studied after the constrained groove pressing (CGP) process. Microstructural observations by scanning electron microscopy and electron backscattered diffraction revealed that after 4 cycles of CGP, a rather homogeneous fine-grained microstructure with an average grain size of 4.3 mu m, and a large fraction of high angle grain boundaries was obtained. By performing shear punch tests (SPT) at different temperatures and various shear strain rates, a peak strain rate sensitivity index (m-value) of 0.49 was obtained after 4 cycles of CGP process at 673 K, while peak m-values of 0.31 and 0.36 were obtained for the as-extruded and 2 cycle CGP process conditions, respectively. An m-value of 0.49 and an activation energy of 113 kJ/mol, obtained for the fine-grained material after 4 cycles of CGP, suggest that the dominant deformation mechanism in the superplastic regime is grain boundary sliding (GBS) controlled by grain boundary diffusion.
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| 9. |
- Hoseini-Athar, Mohammad Mehdi, et al.
(författare)
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Microstructure and superplasticity of Mg-2Gd-xZn alloys processed by equal channel angular pressing
- 2021
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 808
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure, mechanical properties and superplastic behavior of Mg-2Gd-xZn (x = 0, 1, 2 and 3 wt%) alloys were investigated after extrusion and equal channel angular pressing (ECAP). After only 2 passes of ECAP, a homogenous fine-grained microstructure with a grain size of 2.33 mu m and a high fraction of high-angle grain boundaries of 84% were formed in the Mg-2Gd-3Zn (GZ23) alloy, while 4 ECAP passes were necessary to create such a structure in the other alloys. This was attributed to the higher solute drag effect in the other alloys, retarding dynamic recrystallization (DRX). Although DRX occurred more easily in the GZ23 alloy, the final DRX grain size was slightly coarser compared to the other alloys. Shear punch testing (SPT) showed that grain refinement during ECAP leads to a slight increase in the shear yield strength of all studied materials after 2 ECAP passes, which was mostly balanced by texture softening caused by the shear texture component and grain growth after 4 ECAP passes. Contrary to the other alloys, the GZ23 alloy exhibited superplastic behavior after a lower number of ECAP passes. In addition, the superplastic temperature for GZ23 was 648 K, which was lower than the 673 K observed for the other alloys. The m-values of similar to 0.45-0.5 and activation energies of 98-114 kJ/mol suggested grain boundary sliding (GBS) controlled by grain boundary diffusion as the dominant deformation mechanism in the superplastic regime. This was confirmed by microstructural observations.
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| 10. |
- Hoseini-Athar, M. M., et al.
(författare)
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Microstructure, texture, and strain-hardening behavior of extruded Mg-Gd-Zn alloys
- 2020
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Ingår i: Materials Science & Engineering. - : ELSEVIER SCIENCE SA. - 0921-5093 .- 1873-4936. ; 772
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Zn content on the microstructure, texture, mechanical properties and strain-hardening behavior of extruded Mg-2Gd-xZn (x = 0, 1, 2 and 3 wt%) sheets was investigated. Evaluation of texture revealed that while all of the alloys exhibited weak textures, the texture component was altered from a basal to a non-basal one by the addition of Zn. A typical transverse direction (TD) split texture with basal poles rotated about 40 degrees from the normal direction (ND) toward TD was observed for the Zn-containing alloys, the effect being more pronounced at higher Zn contents. Furthermore, the Mg-2Gd-1Zn alloy exhibited the weakest texture due to solute drag imposed by co-segregation of Zn and Gd atoms at grain boundaries. Addition of Zn also resulted in a general increase in yield stress, ultimate tensile strength and elongation along the extrusion direction from 99 to 172 MPa, 178 to 263 MPa, and 25 to 35% for Mg-2Gd and Mg-2Gd-3Zn alloys, respectively. However, increasing Zn content was accompanied by an initial decrease in anisotropy of mechanical properties and strain-hardening behavior, followed by an increase at higher Zn contents. This was due to the difference of orientation of basal planes with regard to tension direction. As a result, lower yield stress, higher elongation and strain-hardening capacity was obtained along TD (with higher Schmid factor for basal slip) compared to ED. It was concluded that excellent mechanical properties and low anisotropy can be achieved in the Mg-2Gd-1Zn alloy.
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