| 1. |
- Long, Doudou, et al.
(författare)
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Improving texture and microstructure homogeneity in high-purity ta sheets by warm cross rolling and annealing
- 2021
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of texture and microstructure uniformity in high-purity tantalum (Ta) sheets during 135◦ warm cross rolling (WCR) was analyzed in detail. X-ray diffraction suggested that relatively uniform ‘ideal’ deformation texture distribution across the thickness could be obtained from WCR, since more potential slip systems could be activated. Electron backscatter diffraction (EBSD) results indicated that the change in strain path in warm rolling could enhance dislocations mobility and increase the probability of dislocations rearrangement and annihilation. Thus, the proportion of low-angle grain boundaries was significantly reduced, and more sub-grain boundaries or sub-grains were formed via WCR. The calculation of geometrically necessary dislocation density based on the strain gradient model supports this result. The analysis of relative Schmid factor combined with the strain contouring map indicated that inhomogeneous orientation-dependent grain subdivision could be effectively weakened, and relatively uniform strain distribution could be formed in the WCR sample. Upon annealing, uniform fine grain size and more randomly oriented grains were obtained in the WCR sample after the completion of recrystallization because of relatively uniform grain subdivision and stored energy distribution.
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| 2. |
- Zhu, Jialin, et al.
(författare)
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Asymmetric cross rolling : A new technique for alleviating orientation-dependent microstructure inhomogeneity in tantalum sheets
- 2020
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Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 9:3, s. 4566-4577
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Tidskriftsartikel (refereegranskat)abstract
- New rolling technique, i.e. asymmetric rolling combined with cross rolling is adopted to produce Ta sputtering targets in this study. Electron backscatter diffraction (EBSD) analysis suggests that (111) and (100) deformed grains distribute alternately along normal direction in cross rolling (CR) and asymmetric cross rolling (ACR) samples. Misorientation angle distribution indicates that severe orientation-dependent grain fragmentation exists in the CR sample, which is also confirmed by kernel average misorientation and grain reference orientation deviation-hyper. Grain average misorientation (GAM) and distribution of geometrically necessary dislocations (GNDs) suggest that the effect of increasing shear strain introduced by asymmetric rolling on deformation microstructure is mainly reflected in the (100) grains, which is further verified by orientation-dependent microhardness values. The computation of Schmid factor indicates that slip within (100) grains in the ACR sample is easier, and the system with higher Schmid factor can alone accommodate the majority of plastic strain. Transmission electron microscopy (TEM) reveals that dense dislocation walls (DDWs) are formed within the (100) deformed grains in the ACR sample, while only sparse dislocation lines can be observed in the CR sample. X-ray line profile analysis (XLPA) displays that ACR can significantly increase the stored energy of the (100) deformed grains and thus weaken the orientation-dependent stored energy distribution. The enhanced recrystallization ability of the (100) grains in the ACR sample facilitates homogenization of the annealing microstructure.
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| 3. |
- Zhu, Jialin, et al.
(författare)
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Enhancing the {100} grain subdivision in high-purity tantalum sheets by asymmetric cross rolling
- 2020
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 166
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Tidskriftsartikel (refereegranskat)abstract
- Weak subdivision or fragmentation ability of deformed {100} (<100> // ND, normal direction) grains by traditional unidirectional (symmetric) rolling results in uneven deformation during tantalum (Ta) processing. Thus, a recently developed asymmetric cross rolling (ACR) is adopted in this work to enhance the subdivision of {100} grain in Ta sheets. Electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and Vickers hardness (HV) were used for the characterisation of microstructure in deformed {100} grains. It is shown that added shear strain component in the ACR leads to heterogeneous deformation substructures within {100} grains. The increase of speed ratio in ACR further enhances the subdivision of deformed {100} grains and thus increases the density of geometrically necessary dislocations (GNDs) in them. The computation of the largest Schmid factor (SFrolling) along with Taylor model suggests that the ACR promotes easier slip within deformed {100} grains. Therefore, the necessary total shear strain contributing to the increase of GNDs density is small. By contrast, the shear strain accumulated after CR-1.0 is distributed more evenly in each slip system resulting in rather sparse distribution of dislocation lines.
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| 4. |
- Zhu, Jialin, et al.
(författare)
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Strain dependence of deformation and recrystallization microstructure homogeneity in clock-rolled tantalum sheets
- 2020
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 161
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure and crystallographic texture are the key factors that determine the sputtering target properties. Clock rolling plays an important role in improving the microstructure homogeneity, but the effect of strain during rolling on deformation and recrystallization behavior is not clear. Thus, high-purity tantalum (Ta) plates were 135° clock rolled to 70% and 87% reduction and then annealed at various temperatures to observe the microstructure evolution. Texture and microstructure in the center layer of the rolled and annealed Ta sheets were characterized via optical microscope (OM), X-ray diffraction (XRD), electron backscatter diffracting (EBSD) and transmission electron microscope (TEM). The results displayed that significant microstructure difference existed between 70% and 87% sample. Grain average misorientation value of {111} grains {〈111〉//normal direction (ND)} in the 70% sample was considerably higher than that in the 87% sample, suggesting a more heterogeneous grain fragmentation. Schmid factor (SFrolling) and Taylor model analysis of {111} grains in the 70% sample demonstrated that the slip was easier, and the system with higher SFrolling could alone accommodate the majority of plastic strain, contributing to the formation of micoshear bands. Upon annealing, the sample rolled 70% recrystallized more quickly, owing to strong {111} deformed texture, and severe microstructure subdivision and great stored energy within {111} grains. The {111} texture is very strong and grain size distribution was not uniform after the completion of recrystallization. However, after annealing of sample rolled 87%, smaller average grain size and variation, and relatively homogeneous texture distribution can be obtained.
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| 5. |
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| 6. |
- Wang, Wei, et al.
(författare)
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Carbon-supported phosphatized CuNi nanoparticle catalysts for hydrazine electrooxidation
- 2019
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 44:21, s. 10637-10645
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Tidskriftsartikel (refereegranskat)abstract
- Developing non-noble metal catalysts with high performance to reduce the cost of hydrazine fuel cells is urgent. Herein, in this study, a series of carbon-supported phosphatized CuNi catalysts (P--CuxNiy/C) are designed for hydrazine oxidation reaction (HzOR) via high temperature phosphating process. Among them, the P-Cu2Ni/C is found to be a promising candidate for hydrazine electrooxidation. Electrochemical measurement results indicate that the P-Cu2Ni/C catalyst exhibits higher catalytic activity and stability for HzOR in comparison with P-CuNi/C, P-CuNi2/C, Cu2Ni/C, Cu/C and Ni/C catalysts. Additionally, HzOR kinetics are also investigated, and it proves that hydrazine electrooxidation on P-Cu2Ni/C is a diffusion controlled irreversible process. Meanwhile, physical characterization reveals that the catalysts have doped phosphorus successfully. All results demonstrate that as-prepared P-Cu2Ni/C catalyst is a promising electrocatalyst for direct hydrazine fuel cells.
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