Dong-Ik Kim | Korea Institute Of Science And Technology (original) (raw)
Papers by Dong-Ik Kim
Journal of Microscopy, 2004
Crystallographic properties of silicide mediated crystalllzation (SMC) polycrystalline silicon (p... more Crystallographic properties of silicide mediated crystalllzation (SMC) polycrystalline silicon (poly Si) and excimer laser annealing (ELA) poly Si were studied by electron backscattered diffraction. Large-grain sized poly Si with a large fraction of low-angle grain boundaries was acquired by SMC. and smallgrain sized poly Si with high-angle grain boundaries especially around 600 was acquired by ELA. The thin film transistor (TFT) device characteristics were investigated in view of short-range crystallinity (pattern quality) and lang-range crystallinity (misorientation distribution) of the specimens. Short-range crystallinity did not significantly affect the TFT device characteristics. and lang-range crystallinity considering the low energy level of special boundaries couldbe better related to the TFT device characteristics of poly Si.
Materials Science and Engineering: A, 2012
In the present study, asymmetric rolling was carried out for incorporating a shear component duri... more In the present study, asymmetric rolling was carried out for incorporating a shear component during the rolling at different temperatures, and was compared with conventional (symmetric) rolling. The microstructures were investigated using electron back-scatter diffraction (EBSD). The strain incorporated was compared with the help of grain orientation spread (GOS). GOS was eventually used as a criterion to partition the microstructure for separating the deformed and the dynamically recrystallized (DRX) grains. The texture of the partitioned DRX grains was shifted by ∼30 • along the c-axis from the deformed grains. The mechanism of dynamic recrystallization (DRX) has been identified as continuous dynamic recovery and recrystallization (CDRR). The partitioned deformed grains for the higher temperature rolled specimens exhibited a texture similar to the room temperature rolled specimen. The asymmetric rolling introduces a shear component which shifts the texture fibre by ∼5-10 • from the conventional rolling texture. This led to an increase in ductility with little compromise on strength.
Journal of Vacuum Science & Technology a, 2004
Low-temperature polycrystalline silicon ͑poly-Si͒ is of increasing interest for the display on gl... more Low-temperature polycrystalline silicon ͑poly-Si͒ is of increasing interest for the display on glass. Among several techniques for the low-temperature poly-Si the Ni-mediated crystallization of amorphous silicon ͑a-Si͒ is promising one. We studied the crystalline orientation of the disk-shaped grains in the poly-Si formed by Ni-mediated crystallization of a-Si using a SiO 2 nanocap by electron backscattered diffraction measurements. A SiO 2 nanocap layer was formed by O 2 plasma treatment on a-Si and an ultrathin Ni layer was deposited on the nanocap. It was heated in a UV scan system for crystallization. The Ni atoms in a-Si diffused through the nanocap and formed NiSi 2 crystallites. Disk-shaped grains were then grown from these nuclei. The size of disk-shaped grains in poly-Si increases from ϳ6 to ϳ20 m when the thickness of nanocap on a-Si changes from 2.4 to 3.2 nm. On the other hand, without the nanocap layer, its size is ϳ3.5 m. The crystalline quality of poly-Si is improved by introducing a nanocap layer, which is due mainly to the increase of the grain size.
Thin Solid Films, 2005
ABSTRACT This study focuses on the structures and the crystallographic orientations of copper ele... more ABSTRACT This study focuses on the structures and the crystallographic orientations of copper electrodeposits in trench patterns by the electron backscattered diffraction (EBSD) technique. The EBSD measurement was made on the surface of annealed deposits before and after removal of their over-plated layers by chemical mechanical polishing (CMP) and also on the section normal to trench lines. The textures of the annealed deposit with and without the over-plated layer are almost same. The major and minor orientation components in the annealing textures of trench specimens were approximated by {111}〈110〉 and its twin components, {115}〈110〉 and {115}〈141〉, respectively. Here {hkl}〈uvw〉 indicates that {hkl} is the crystallographic planes parallel to the trench base plane and 〈uvw〉 is the crystallographic directions parallel to the trench line direction. By measuring the line-normal sectional EBSD analysis, the copper electrodeposit in a trench plug is figured as a single crystal having a few of twinning, and hence the over-plated layer has almost the same texture as the trench plug. Therefore, the texture of trench plugs can be inferred by that of the over-plated layer.
Isij International, 2006
ABSTRACT
Scripta Materialia, 2007
This study investigated the fracture behaviour of cohesive cracking and subsequent buckling delam... more This study investigated the fracture behaviour of cohesive cracking and subsequent buckling delamination at the interface between a diamond-like carbon (DLC) film and a stainless steel substrate during tension testing. It was revealed by cross-sectional analysis with a ...
Journal of Applied Physics, 2008
Acta Materialia, 2009
... Klug and Alexander [14] suggested Eq. (2) as a means to separate size and strain contribution... more ... Klug and Alexander [14] suggested Eq. (2) as a means to separate size and strain contributions by assuming Gaussian strain broadening and Lorentzian size broadening:(2) where δ2θ is in radians, θ 0 is the position of the peak maximum, K (= 0.9) is the shape factor in ...
Journal of Nuclear Materials, 2009
We present tungsten alloy coating of 150-200 lm thickness with improved plasma erosion resistance... more We present tungsten alloy coating of 150-200 lm thickness with improved plasma erosion resistance fabricated by plasma spraying of granular W-SiC composite powders. During increasing the SiC concentration to 8 wt%, we observed the increase in the hardness of the coating from 250 to 440 Hv. The plasma erosion depth of the coating decreased by 10 times compared with pure tungsten in the same erosion environment.
Journal of Nuclear Materials, 2009
... During neutron irradiation, it is known that fine (230 nm in diameter) bcc Cr-rich precipita... more ... During neutron irradiation, it is known that fine (230 nm in diameter) bcc Cr-rich precipitates (α′) are formed in high Cr steels, in addition to clusters of vacancies and self-interstitial defects [2], [3], [4], [5], [6] and [7]. Little and Stow [2] used transmission electron microscopy (TEM ...
Acta Materialia, 2009
Asymmetric rolling of commercially pure magnesium was carried out at three different temperatures... more Asymmetric rolling of commercially pure magnesium was carried out at three different temperatures: room temperature, 200°C and 350°C. Systematic analysis of microstructures, grain size distributions, texture and misorientation distributions were performed using electron backscattered diffraction in a field emission gun scanning electron microscope. The results were compared with conventional (symmetric) rolling carried out under the same conditions of temperature and strain rate. Simulations of deformation texture evolution were performed using the viscoplastic self-consistent polycrystal plasticity model. The main trends of texture evolution are faithfully reproduced by the simulations for the tests at room temperature. The deviations that appear for the textures obtained at high temperature can be explained by the occurrence of dynamic recrystallization. Finally, the mechanisms of texture evolution in magnesium during asymmetric and symmetric rolling are explained with the help of ideal orientations, grain velocity fields and divergence maps displayed in orientation space.
Materials Letters, 2010
This paper suggests a novel method for improving the ductility of magnesium alloy sheets using a ... more This paper suggests a novel method for improving the ductility of magnesium alloy sheets using a laser scanning treatment combined with a defocusing technique. The crystallographic orientation on both surface regions of the AZ31B magnesium alloy sheet processed using this method was changed from a strong basal texture to an almost random texture. The laser-scanned magnesium alloy sheet showed enhanced tensile elongation of up to 50% with a similar a tensile strength.
Electrochemical and Solid State Letters, 2010
... by Carbon Ion Implantation. [Electrochemical and Solid-State Letters 13, B40 (2010)]. Seung H... more ... by Carbon Ion Implantation. [Electrochemical and Solid-State Letters 13, B40 (2010)]. Seung Hee Hong, Madakashira P. Phaniraj, Dong-Ik Kim, Jae-Pyoung Ahn, Young Whan Cho, Seung Hee Han, Heung Nam Han. Abstract. ...
Materials Science and Technology, 2010
ABSTRACT Hot deformation behaviour of hypereutectoid steels (0.83-0.92%C) alloyed with 0-2%Al is ... more ABSTRACT Hot deformation behaviour of hypereutectoid steels (0.83-0.92%C) alloyed with 0-2%Al is investigated. Compression tests were carried out in the temperature range 1000-1100 degrees C at 0.1-10 s(-1) strain rates. The stress-strain curves are analysed using work hardening rate flow stress plots to determine the critical and peak stress and the corresponding strains associated with dynamic recrystallisation. The addition of Al increases the strain hardening rate and lowers the peak strain. There is an optimum content beyond which peak strain increases with Al addition. Phase diagram calculations show that the multiphase microstructure present during deformation is responsible for the non-linear effect of Al. The steady state stress is modelled using the sine hyperbolic constitutive equation, and the activation energy for deformation is determined.
Corrosion Science, 2010
Cyclic oxidation of austenitic steels (Fe-20Ni-14Cr-2.5Mo-2Mn-2.5Al-wt.%) dispersed with 0, 0.5 a... more Cyclic oxidation of austenitic steels (Fe-20Ni-14Cr-2.5Mo-2Mn-2.5Al-wt.%) dispersed with 0, 0.5 and 5 wt.% yttria was carried out at 800°C in air. The scale surface and cross-section were characterized using X-ray diffraction, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). Yttria additions improve the resistance to spallation. The increase in the resistance to spallation appears to be related to the presence of mixed oxides between yttria and base metal oxides.
Corrosion Science, 2011
... Kim, KY Kim, Effect of reactive elements on oxidation behaviour of Fe 22Cr 0.5Mn ferritic sta... more ... Kim, KY Kim, Effect of reactive elements on oxidation behaviour of Fe 22Cr 0.5Mn ferritic stainless steel for a solid oxide fuel cell interconnect, J. Power Sources 178 (2008) 1-8 [4] T. Horita, H. Kishimoto, K. Yamaji, Y. Xiong ... 152 (2005) A1896-A1901 [6] SH Hong, MP Phaniraj, DI. ...
Corrosion Science, 2012
ABSTRACT We examined the corrosion behavior of Mg in Hanks’ solution to determine the potential o... more ABSTRACT We examined the corrosion behavior of Mg in Hanks’ solution to determine the potential of a biodegradable pure Mg implant. Abrupt corrosion, initiated by Fe impurity, was observed in the latter stage of experimentation in the form of preferred crystallographic pitting (PCP) propagating along the (0 0 0 1) basal plane in the grain. Herein, we report the mechanism behind PCP corrosion of Mg and evaluate potential solutions to suppress PCP corrosion. In particular, the addition of Mn inhibits PCP initiation by converting Fe impurities to Fe-Mn compounds, while refining the grain size by extrusion reduces PCP propagation.
Scripta Materialia, 2012
... 9]; T. Duerig; Mater. Sci. Eng. A, 69 (2006), pp. 438–440. [10]; E. Goo, T. Duerig, K. Melton... more ... 9]; T. Duerig; Mater. Sci. Eng. A, 69 (2006), pp. 438–440. [10]; E. Goo, T. Duerig, K. Melton, R. Sinclair; Acta Metall., 33 (1985), p. 1725. ...
Current Applied Physics, 2012
Thin sheets of V 85 Al 10 Co 5 alloy were produced by a thermo-mechanical treatment consisting in... more Thin sheets of V 85 Al 10 Co 5 alloy were produced by a thermo-mechanical treatment consisting in successive hot rolling, cold rolling steps and annealing treatment at high temperature followed by either air cooling or water quenching. Though the values of hydrogen permeability measured for these sheets were significantly reduced as a consequence of the rolling process, the annealing treatment restored almost the hydrogen permeation properties to those of the alloy in the cast condition. EBSD analyses suggested that the post-annealing treatment performed at 1100 C for 3 min after cold rolling induced a recrystallization of the grains resulting in a preferred orientation along the {002} planes. For the sample annealed and water quenched, the value of the hydrogen flux reached about 45 ml/cm 2 .min, which is more than twice the value of the flux obtained for thin foils of Pd alloys tested under identical conditions.
Journal of the American Ceramic Society, 2012
ABSTRACT Lanthanum silicates with different lanthanum concentrations La9.33+x(SiO4)6O2+1.5x were ... more ABSTRACT Lanthanum silicates with different lanthanum concentrations La9.33+x(SiO4)6O2+1.5x were prepared by solid state reaction using milling procedures of different degrees and sintered at 1700 degrees C or 1750 degrees C. The phase composition and the microstructural evolution were shown to depend strongly on the heat-treatment temperature and history. The presence of the liquid phase in the lanthanum-rich compositions at sintering temperatures is clearly evidenced, which, however, is not in accordance with the known phase relations of the material. Exaggerated growth of plate-shaped grains in the c-axis direction was induced by the inhomogeneous presence of the liquid phase. The solid solution region with excess lanthanum appears to extend with increasing temperature, as evidenced by intragranular second phase precipitation on heat treatments at lower temperature as well as the X-ray powder diffraction results of differently treated samples. Lanthanum-deficient compositions were shown to exist as a two-phase mixture with La2Si2O7 in equilibrium, although the powders prepared by solid state reaction at 1300 degrees C do not indicate the significant presence of a secondary phase, regardless of the composition. The groove profiles with both a maximum and minimum (or hump) indicate the surface diffusion mechanism controlled by bulk defect chemistry and defect migration in the material. This phenomenon can be explained by the transport anisotropy in La diffusion which controls the matter transport by the bulk ambipolar diffusion mechanism, supported by recent theoretical as well as experimental studies. Electron backscattered diffraction mapping clearly correlated the grains perpendicular to the c-axis with the strong development of thermal grooving and vice versa by the transport anisotropy. There is little indication of the surface and grain-boundary energy anisotropy regardless of the compositions.
Journal of Microscopy, 2004
Crystallographic properties of silicide mediated crystalllzation (SMC) polycrystalline silicon (p... more Crystallographic properties of silicide mediated crystalllzation (SMC) polycrystalline silicon (poly Si) and excimer laser annealing (ELA) poly Si were studied by electron backscattered diffraction. Large-grain sized poly Si with a large fraction of low-angle grain boundaries was acquired by SMC. and smallgrain sized poly Si with high-angle grain boundaries especially around 600 was acquired by ELA. The thin film transistor (TFT) device characteristics were investigated in view of short-range crystallinity (pattern quality) and lang-range crystallinity (misorientation distribution) of the specimens. Short-range crystallinity did not significantly affect the TFT device characteristics. and lang-range crystallinity considering the low energy level of special boundaries couldbe better related to the TFT device characteristics of poly Si.
Materials Science and Engineering: A, 2012
In the present study, asymmetric rolling was carried out for incorporating a shear component duri... more In the present study, asymmetric rolling was carried out for incorporating a shear component during the rolling at different temperatures, and was compared with conventional (symmetric) rolling. The microstructures were investigated using electron back-scatter diffraction (EBSD). The strain incorporated was compared with the help of grain orientation spread (GOS). GOS was eventually used as a criterion to partition the microstructure for separating the deformed and the dynamically recrystallized (DRX) grains. The texture of the partitioned DRX grains was shifted by ∼30 • along the c-axis from the deformed grains. The mechanism of dynamic recrystallization (DRX) has been identified as continuous dynamic recovery and recrystallization (CDRR). The partitioned deformed grains for the higher temperature rolled specimens exhibited a texture similar to the room temperature rolled specimen. The asymmetric rolling introduces a shear component which shifts the texture fibre by ∼5-10 • from the conventional rolling texture. This led to an increase in ductility with little compromise on strength.
Journal of Vacuum Science & Technology a, 2004
Low-temperature polycrystalline silicon ͑poly-Si͒ is of increasing interest for the display on gl... more Low-temperature polycrystalline silicon ͑poly-Si͒ is of increasing interest for the display on glass. Among several techniques for the low-temperature poly-Si the Ni-mediated crystallization of amorphous silicon ͑a-Si͒ is promising one. We studied the crystalline orientation of the disk-shaped grains in the poly-Si formed by Ni-mediated crystallization of a-Si using a SiO 2 nanocap by electron backscattered diffraction measurements. A SiO 2 nanocap layer was formed by O 2 plasma treatment on a-Si and an ultrathin Ni layer was deposited on the nanocap. It was heated in a UV scan system for crystallization. The Ni atoms in a-Si diffused through the nanocap and formed NiSi 2 crystallites. Disk-shaped grains were then grown from these nuclei. The size of disk-shaped grains in poly-Si increases from ϳ6 to ϳ20 m when the thickness of nanocap on a-Si changes from 2.4 to 3.2 nm. On the other hand, without the nanocap layer, its size is ϳ3.5 m. The crystalline quality of poly-Si is improved by introducing a nanocap layer, which is due mainly to the increase of the grain size.
Thin Solid Films, 2005
ABSTRACT This study focuses on the structures and the crystallographic orientations of copper ele... more ABSTRACT This study focuses on the structures and the crystallographic orientations of copper electrodeposits in trench patterns by the electron backscattered diffraction (EBSD) technique. The EBSD measurement was made on the surface of annealed deposits before and after removal of their over-plated layers by chemical mechanical polishing (CMP) and also on the section normal to trench lines. The textures of the annealed deposit with and without the over-plated layer are almost same. The major and minor orientation components in the annealing textures of trench specimens were approximated by {111}〈110〉 and its twin components, {115}〈110〉 and {115}〈141〉, respectively. Here {hkl}〈uvw〉 indicates that {hkl} is the crystallographic planes parallel to the trench base plane and 〈uvw〉 is the crystallographic directions parallel to the trench line direction. By measuring the line-normal sectional EBSD analysis, the copper electrodeposit in a trench plug is figured as a single crystal having a few of twinning, and hence the over-plated layer has almost the same texture as the trench plug. Therefore, the texture of trench plugs can be inferred by that of the over-plated layer.
Isij International, 2006
ABSTRACT
Scripta Materialia, 2007
This study investigated the fracture behaviour of cohesive cracking and subsequent buckling delam... more This study investigated the fracture behaviour of cohesive cracking and subsequent buckling delamination at the interface between a diamond-like carbon (DLC) film and a stainless steel substrate during tension testing. It was revealed by cross-sectional analysis with a ...
Journal of Applied Physics, 2008
Acta Materialia, 2009
... Klug and Alexander [14] suggested Eq. (2) as a means to separate size and strain contribution... more ... Klug and Alexander [14] suggested Eq. (2) as a means to separate size and strain contributions by assuming Gaussian strain broadening and Lorentzian size broadening:(2) where δ2θ is in radians, θ 0 is the position of the peak maximum, K (= 0.9) is the shape factor in ...
Journal of Nuclear Materials, 2009
We present tungsten alloy coating of 150-200 lm thickness with improved plasma erosion resistance... more We present tungsten alloy coating of 150-200 lm thickness with improved plasma erosion resistance fabricated by plasma spraying of granular W-SiC composite powders. During increasing the SiC concentration to 8 wt%, we observed the increase in the hardness of the coating from 250 to 440 Hv. The plasma erosion depth of the coating decreased by 10 times compared with pure tungsten in the same erosion environment.
Journal of Nuclear Materials, 2009
... During neutron irradiation, it is known that fine (230 nm in diameter) bcc Cr-rich precipita... more ... During neutron irradiation, it is known that fine (230 nm in diameter) bcc Cr-rich precipitates (α′) are formed in high Cr steels, in addition to clusters of vacancies and self-interstitial defects [2], [3], [4], [5], [6] and [7]. Little and Stow [2] used transmission electron microscopy (TEM ...
Acta Materialia, 2009
Asymmetric rolling of commercially pure magnesium was carried out at three different temperatures... more Asymmetric rolling of commercially pure magnesium was carried out at three different temperatures: room temperature, 200°C and 350°C. Systematic analysis of microstructures, grain size distributions, texture and misorientation distributions were performed using electron backscattered diffraction in a field emission gun scanning electron microscope. The results were compared with conventional (symmetric) rolling carried out under the same conditions of temperature and strain rate. Simulations of deformation texture evolution were performed using the viscoplastic self-consistent polycrystal plasticity model. The main trends of texture evolution are faithfully reproduced by the simulations for the tests at room temperature. The deviations that appear for the textures obtained at high temperature can be explained by the occurrence of dynamic recrystallization. Finally, the mechanisms of texture evolution in magnesium during asymmetric and symmetric rolling are explained with the help of ideal orientations, grain velocity fields and divergence maps displayed in orientation space.
Materials Letters, 2010
This paper suggests a novel method for improving the ductility of magnesium alloy sheets using a ... more This paper suggests a novel method for improving the ductility of magnesium alloy sheets using a laser scanning treatment combined with a defocusing technique. The crystallographic orientation on both surface regions of the AZ31B magnesium alloy sheet processed using this method was changed from a strong basal texture to an almost random texture. The laser-scanned magnesium alloy sheet showed enhanced tensile elongation of up to 50% with a similar a tensile strength.
Electrochemical and Solid State Letters, 2010
... by Carbon Ion Implantation. [Electrochemical and Solid-State Letters 13, B40 (2010)]. Seung H... more ... by Carbon Ion Implantation. [Electrochemical and Solid-State Letters 13, B40 (2010)]. Seung Hee Hong, Madakashira P. Phaniraj, Dong-Ik Kim, Jae-Pyoung Ahn, Young Whan Cho, Seung Hee Han, Heung Nam Han. Abstract. ...
Materials Science and Technology, 2010
ABSTRACT Hot deformation behaviour of hypereutectoid steels (0.83-0.92%C) alloyed with 0-2%Al is ... more ABSTRACT Hot deformation behaviour of hypereutectoid steels (0.83-0.92%C) alloyed with 0-2%Al is investigated. Compression tests were carried out in the temperature range 1000-1100 degrees C at 0.1-10 s(-1) strain rates. The stress-strain curves are analysed using work hardening rate flow stress plots to determine the critical and peak stress and the corresponding strains associated with dynamic recrystallisation. The addition of Al increases the strain hardening rate and lowers the peak strain. There is an optimum content beyond which peak strain increases with Al addition. Phase diagram calculations show that the multiphase microstructure present during deformation is responsible for the non-linear effect of Al. The steady state stress is modelled using the sine hyperbolic constitutive equation, and the activation energy for deformation is determined.
Corrosion Science, 2010
Cyclic oxidation of austenitic steels (Fe-20Ni-14Cr-2.5Mo-2Mn-2.5Al-wt.%) dispersed with 0, 0.5 a... more Cyclic oxidation of austenitic steels (Fe-20Ni-14Cr-2.5Mo-2Mn-2.5Al-wt.%) dispersed with 0, 0.5 and 5 wt.% yttria was carried out at 800°C in air. The scale surface and cross-section were characterized using X-ray diffraction, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). Yttria additions improve the resistance to spallation. The increase in the resistance to spallation appears to be related to the presence of mixed oxides between yttria and base metal oxides.
Corrosion Science, 2011
... Kim, KY Kim, Effect of reactive elements on oxidation behaviour of Fe 22Cr 0.5Mn ferritic sta... more ... Kim, KY Kim, Effect of reactive elements on oxidation behaviour of Fe 22Cr 0.5Mn ferritic stainless steel for a solid oxide fuel cell interconnect, J. Power Sources 178 (2008) 1-8 [4] T. Horita, H. Kishimoto, K. Yamaji, Y. Xiong ... 152 (2005) A1896-A1901 [6] SH Hong, MP Phaniraj, DI. ...
Corrosion Science, 2012
ABSTRACT We examined the corrosion behavior of Mg in Hanks’ solution to determine the potential o... more ABSTRACT We examined the corrosion behavior of Mg in Hanks’ solution to determine the potential of a biodegradable pure Mg implant. Abrupt corrosion, initiated by Fe impurity, was observed in the latter stage of experimentation in the form of preferred crystallographic pitting (PCP) propagating along the (0 0 0 1) basal plane in the grain. Herein, we report the mechanism behind PCP corrosion of Mg and evaluate potential solutions to suppress PCP corrosion. In particular, the addition of Mn inhibits PCP initiation by converting Fe impurities to Fe-Mn compounds, while refining the grain size by extrusion reduces PCP propagation.
Scripta Materialia, 2012
... 9]; T. Duerig; Mater. Sci. Eng. A, 69 (2006), pp. 438–440. [10]; E. Goo, T. Duerig, K. Melton... more ... 9]; T. Duerig; Mater. Sci. Eng. A, 69 (2006), pp. 438–440. [10]; E. Goo, T. Duerig, K. Melton, R. Sinclair; Acta Metall., 33 (1985), p. 1725. ...
Current Applied Physics, 2012
Thin sheets of V 85 Al 10 Co 5 alloy were produced by a thermo-mechanical treatment consisting in... more Thin sheets of V 85 Al 10 Co 5 alloy were produced by a thermo-mechanical treatment consisting in successive hot rolling, cold rolling steps and annealing treatment at high temperature followed by either air cooling or water quenching. Though the values of hydrogen permeability measured for these sheets were significantly reduced as a consequence of the rolling process, the annealing treatment restored almost the hydrogen permeation properties to those of the alloy in the cast condition. EBSD analyses suggested that the post-annealing treatment performed at 1100 C for 3 min after cold rolling induced a recrystallization of the grains resulting in a preferred orientation along the {002} planes. For the sample annealed and water quenched, the value of the hydrogen flux reached about 45 ml/cm 2 .min, which is more than twice the value of the flux obtained for thin foils of Pd alloys tested under identical conditions.
Journal of the American Ceramic Society, 2012
ABSTRACT Lanthanum silicates with different lanthanum concentrations La9.33+x(SiO4)6O2+1.5x were ... more ABSTRACT Lanthanum silicates with different lanthanum concentrations La9.33+x(SiO4)6O2+1.5x were prepared by solid state reaction using milling procedures of different degrees and sintered at 1700 degrees C or 1750 degrees C. The phase composition and the microstructural evolution were shown to depend strongly on the heat-treatment temperature and history. The presence of the liquid phase in the lanthanum-rich compositions at sintering temperatures is clearly evidenced, which, however, is not in accordance with the known phase relations of the material. Exaggerated growth of plate-shaped grains in the c-axis direction was induced by the inhomogeneous presence of the liquid phase. The solid solution region with excess lanthanum appears to extend with increasing temperature, as evidenced by intragranular second phase precipitation on heat treatments at lower temperature as well as the X-ray powder diffraction results of differently treated samples. Lanthanum-deficient compositions were shown to exist as a two-phase mixture with La2Si2O7 in equilibrium, although the powders prepared by solid state reaction at 1300 degrees C do not indicate the significant presence of a secondary phase, regardless of the composition. The groove profiles with both a maximum and minimum (or hump) indicate the surface diffusion mechanism controlled by bulk defect chemistry and defect migration in the material. This phenomenon can be explained by the transport anisotropy in La diffusion which controls the matter transport by the bulk ambipolar diffusion mechanism, supported by recent theoretical as well as experimental studies. Electron backscattered diffraction mapping clearly correlated the grains perpendicular to the c-axis with the strong development of thermal grooving and vice versa by the transport anisotropy. There is little indication of the surface and grain-boundary energy anisotropy regardless of the compositions.