scholarly journals Nanocompositional Electron Microscopic Analysis and Role of Grain Boundary Phase of Isotropically Oriented Nd-Fe-B Magnets

2017 ◽  
Vol 2017 ◽  
pp. 1-17 ◽  
Author(s):  
Gregor A. Zickler ◽  
Josef Fidler
Keyword(s):  
Domain Wall ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Magnetization Reversal ◽  
Coercive Field ◽  
Microscopic Analysis ◽  
Realistic Model ◽  
Boundary Phase ◽  
Electron Microscopic ◽  
The Impact

Nanoanalytical TEM characterization in combination with finite element micromagnetic modelling clarifies the impact of the grain misalignment and grain boundary nanocomposition on the coercive field and gives guidelines how to improve coercivity in Nd-Fe-B based magnets. The nanoprobe electron energy loss spectroscopy measurements obtained an asymmetric composition profile of the Fe-content across the grain boundary phase in isotropically oriented melt-spun magnets and showed an enrichment of iron up to 60 at% in the Nd-containing grain boundaries close to Nd2Fe14B grain surfaces parallel to the c-axis and a reduced iron content up to 35% close to grain surfaces perpendicular to the c-axis. The numerical micromagnetic simulations on isotropically oriented magnets using realistic model structures from the TEM results reveal a complex magnetization reversal starting at the grain boundary phase and show that the coercive field increases compared to directly coupled grains with no grain boundary phase independently of the grain boundary thickness. This behaviour is contrary to the one in aligned anisotropic magnets, where the coercive field decreases compared to directly coupled grains with an increasing grain boundary thickness, if Js value is > 0.2 T, and the magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries at the prismatic planes parallel to the c-axis and secondly as Néel domain wall at the basal planes perpendicular to the c-axis. In summary our study shows an increase of coercive field in isotropically oriented Nd-Fe-B magnets for GB layer thickness > 5 nm and an average Js value of the GB layer < 0.8 T compared to the magnet with perfectly aligned grains.

scholarly journals A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Gregor A. Zickler ◽  
Josef Fidler ◽  
Johannes Bernardi ◽  
Thomas Schrefl ◽  
Ahmad Asali
Keyword(s):  
Domain Wall ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Coercive Field ◽  
Boundary Phase ◽  
Micromagnetic Simulations ◽  
Fe Content ◽  
Néel Domain Wall ◽  
High Resolution Tem ◽  
Numerical Finite Element

The nanoanalytical high resolution TEM/STEM investigation of the intergranular grain boundary phase of anisotropic sintered and rapidly quenched heavy rare earth-free Nd-Fe-B magnet materials revealed a difference in composition for grain boundaries parallel (large Fe-content) and perpendicular (low Fe content) to the alignment direction. This behaviour vanishes in magnets with a high degree of misorientation. The numerical finite element micromagnetic simulations are based on the anisotropic compositional behaviour of GBs and show a decrease of the coercive field with an increasing thickness of the grain boundary layer. The magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries parallel to thec-axis and secondly as Néel domain wall perpendicular to thec-axis into the adjacent hard magnetic grains. The increasing misalignment of grains leads to the loss of the anisotropic compositional behaviour and therefore to an averaged value of the grain boundary composition. In this case the simulations show an increase of the coercive field compared to the anisotropic magnet. The calculated coercive field values of the investigated magnet samples are in the order ofμ0HcJ=1.8 T–2.1 Tfor a mean grain boundary thickness of 4 nm, which agrees perfectly with the experimental data.

scholarly journals Molecular Dynamics Study on the Impact of Cu Clusters at the BCC-Fe Grain Boundary on the Tensile Properties of Crystal

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1533
Author(s):  
Haichao Zhang ◽  
Xufeng Wang ◽  
Huirong Li ◽  
Changqing Li ◽  
Yungang Li
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Tensile Properties ◽  
Structural Phase ◽  
Structural Phase Transformation ◽  
Tensile Process ◽  
Deformation Ability ◽  
The Impact

The molecular dynamics (MD) method was used to simulate and calculate the segregation energy and cohesive energy of Cu atoms at the Σ3{111}(110) and Σ3{112}(110) grain boundaries, and the tensile properties of the BCC-Fe crystal, with the grain boundaries containing coherent Cu clusters of different sizes (a diameter of 10 Å, 15 Å and 20 Å). The results showed that Cu atoms will spontaneously segregate towards the grain boundaries and tend to exist in the form of large-sized, low-density Cu clusters at the grain boundaries. When Cu cluster exists at the Σ3{111}(110) grain boundary, the increase in the size of the Cu cluster leads to an increase in the probability of vacancy formation inside the Cu cluster during the tensile process, weakening the breaking strength of the crystal. When the Cu cluster exists at the Σ3{112}(110) grain boundary, the Cu cluster with a diameter of 10 Å will reduce the strain hardening strength of the crystal, but the plastic deformation ability of the crystal will not be affected, and the existence of Cu clusters with a diameter of 15 Å and 20 Å will suppress the structural phase transformation of the crystal, and significantly decrease the plastic deformation ability of the crystal, thereby resulting in embrittlement of the crystal.

GRAIN BOUNDARIES: PHASE TRANSITIONS AND CRITICAL PHENOMENA

1991 ◽  
Vol 05 (19) ◽  
pp. 2989-3028 ◽  
Author(s):  
E.I. RABKIN ◽  
L.S. SHVINDLERMAN ◽  
B.B. STRAUMAL
Keyword(s):  
Phase Transitions ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Critical Phenomena ◽  
External Surface ◽  
Theoretical Models ◽  
Boundary Structure ◽  
Boundary Phase ◽  
Recent Experimental Data ◽  
Grain Boundary Structure

Recent theories of grain boundary structure have been reviewed briefly. The possibility of existence of the same variety of phase transitions on grain boundaries as that on the crystal external surface has been demonstrated. Recent experimental data and theoretical models concerning grain boundary phase transitions are critically analysed. Grain boundary phase transitions connected with the formation of thin disordered layers on the boundary (prewetting, premelting) are particularly distinguished. Results of recent indirect experiments, which may be treated in terms of prewetting and premelting, have been reviewed. Experimentally observed critical phenomena in the vicinity of the prewetting transition on the tin-germanium interphase boundary have been discussed in terms of the critical exponents theory. Some ideas regarding directions of further research are presented.

Grain Boundary Phase Analysis of Silicon Nitride by a Newly Developed 300kv Field-Emission Electron Microscope

1994 ◽  
Vol 346 ◽  
Author(s):  
Y. Bando ◽  
H. Suematsu ◽  
M. Mitomo
Keyword(s):  
Electron Microscope ◽  
Silicon Nitride ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Phase Analysis ◽  
Field Emission ◽  
Boundary Phase ◽  
Emission Electron ◽  
Triple Points

ABSTRACTThe grain boundary phase of silicon nitride containing additives Y2O3 and Nd2O3 has been studied by means of a newly developed 300kV field emission ATEM. The composition of the two-grain boundary phase of about 1 nm thick is successfully determined. It is then found that the compositions among the grain boundaries are not the same and the additives of Y2O3-Nd2O3 are poor in the two-grain boundary, while they are rich in the triple points.

scholarly journals Cardiomyocyte deletion of mitofusin-1 leads to mitochondrial fragmentation and improves tolerance to ROS-induced mitochondrial dysfunction and cell death

2012 ◽  
Vol 302 (1) ◽  
pp. H167-H179 ◽  
Author(s):  
Kyriakos N. Papanicolaou ◽  
Gladys A. Ngoh ◽  
Erinne R. Dabkowski ◽  
Kelly A. O'Connell ◽  
Rogerio F. Ribeiro ◽  
...  
Keyword(s):  
Mitochondrial Dysfunction ◽  
Mitochondrial Permeability Transition ◽  
Microscopic Analysis ◽  
Left Ventricular ◽  
Mitochondrial Morphology ◽  
Mitochondrial Fragmentation ◽  
Electron Microscopic ◽  
Mitofusin 2 ◽  
The Impact

Molecular studies examining the impact of mitochondrial morphology on the mammalian heart have previously focused on dynamin related protein-1 (Drp-1) and mitofusin-2 (Mfn-2), while the role of the other mitofusin isoform, Mfn-1, has remained largely unexplored. In the present study, we report the generation and initial characterization of cardiomyocyte-specific Mfn-1 knockout (Mfn-1 KO) mice. Using electron microscopic analysis, we detect a greater prevalence of small, spherical mitochondria in Mfn-1 KO hearts, indicating that the absence of Mfn-1 causes a profound shift in the mitochondrial fusion/fission balance. Nevertheless, Mfn-1 KO mice exhibit normal left-ventricular function, and isolated Mfn-1 KO heart mitochondria display a normal respiratory repertoire. Mfn-1 KO myocytes are protected from mitochondrial depolarization and exhibit improved viability when challenged with reactive oxygen species (ROS) in the form of hydrogen peroxide (H2O2). Furthermore, in vitro studies detect a blunted response of KO mitochondria to undergo peroxide-induced mitochondrial permeability transition pore opening. These data suggest that Mfn-1 deletion confers protection against ROS-induced mitochondrial dysfunction. Collectively, we suggest that mitochondrial fragmentation in myocytes is not sufficient to induce heart dysfunction or trigger cardiomyocyte death. Additionally, our data suggest that endogenous levels of Mfn-1 can attenuate myocyte viability in the face of an imminent ROS overload, an effect that could be associated with the ability of Mfn-1 to remodel the outer mitochondrial membrane.

Degradation of high-Tc superconductors by annealing in dry and moist atmospheres

1990 ◽  
Vol 5 (9) ◽  
pp. 1855-1859 ◽  
Author(s):  
W-K. Lee ◽  
A. S. Nowick
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Meissner Effect ◽  
Treatment Temperature ◽  
The Other ◽  
Boundary Phase ◽  
Maximum Effect ◽  
High Tc Superconductors ◽  
High Tc ◽  
Anneal Temperature

A study is made of the effects of annealing both La2−xSrxCuO4 (for x = 0, 0.1, and 0.15) and YBa2Cu3O7 in wet and dry O2 atmospheres at various temperatures between 200 and 930 °C. In the case of La2−xSrxSrCuO4, substantial degradation of resistive properties occurs during annealing in moist O2, the degradation being highest at 200 °C and decreasing as the treatment temperature increases. Since the Meissner effect remains unaffected, it is concluded that degradation is due to the formation of a hydroxide species at grain boundaries, which decomposes as the anneal temperature is increased to 930 °C. In the case of YBa2Cu3O7, on the other hand, moisture does not produce degradation for anneals at 200 °C and above, but severe degradation of resistive behavior does occur for dry O2 anneals, with a maximum effect at 500 °C. It is found that this effect results from a contaminant gas, possibly CO2, absorbed by the furnace when it is open to air. Again, the degradation is due to formation of a grain-boundary phase which decomposes by annealing at 930 °C.

Observations of Interaction Between Magnetic Domain Wall and Grain Boundaries in Fe-3wt%Si Alloy by Kerr Microscopy

1999 ◽  
Vol 586 ◽  
Author(s):  
K. Kawahara ◽  
Y. Yagyu ◽  
S. Tsurekawa ◽  
T. Watanabe
Keyword(s):  
Domain Wall ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Domain Structure ◽  
Misorientation Angle ◽  
Magnetic Domain ◽  
Magnetic Domain Structure ◽  
Magnetic Domain Wall ◽  
Domain Structures ◽  
Grain Boundary Plane

ABSTRACTMagnetic domain structures in Fe-3wt%Si alloy have been observed by a Kerr microscopy to understand the interaction between the magnetic domain wall and grain boundaries. It was found that the domain structures in the vicinity of the grain boundary depend on the misorientation angle; the high angle random boundary disturbs the magnetic domain structure more than the low angle boundary. In addition to the misorientation angle, magnetic domain structures were affected by the inclination of the grain boundary plane. Moreover, dynamic observations of rearrangement of the magnetic domain structure during magnetization revealed that grain boundaries could act as the sink and/or the source for magnetic domains.

The Effect of Cu Alloying on Al Alloy Thin Films: Microstructural Mechanisms That Enhance Electromigration Resistance

1993 ◽  
Vol 309 ◽  
Author(s):  
D. R. Frear ◽  
J. R. Michael ◽  
A. D. Romig
Keyword(s):  
Thin Films ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Room Temperature ◽  
Boundary Diffusion ◽  
Boundary Phase ◽  
Al Alloy ◽  
Cu Films ◽  
Isothermal Heat Treatments ◽  
Lower Temperature

AbstractThe microstructural evolution of unpatterned Al-2wt.%Cu thin films has been examined to elucidate the mechanism by which copper improves electromigration resistance. After annealing at 425°C and cooling to room temperature at a rate of approximately 1°C/min., the microstructure of the Al-Cu films consisted of 1 μm aluminum grains with θ-phase Al2Cu precipitates at grain boundaries and triple points. The grain size and precipitation distribution did not change with subsequent isothermal heat treatments in the temperature range of 200° to 400°C. Al-Cu thin films annealed at 400°C, a temperature just below the Al/Al+θ solvus, exhibited microstructures in which the aluminum grain boundaries were depleted in copper except for the presence of the pre-existing large, widely dispersed AI2Cu precipitates. Al-Cu thin films annealed at 200° to 300°C were enriched with copper at the aluminum grain boundaries. The large, widely dispersed Al2Cu precipitates remained after the lower temperature anneals. From these results, it is proposed that the presence of copper in aluminum thin films improves electromigration resistance due to the precipitation of a thin film of Al2Cu, or a substoichiometric precursor, along the grain boundaries. The grain boundary phase retards grain boundary diffusion in the thin films, thereby reducing total mass transport and improving electromigration resistance.

scholarly journals Protective Alumina Scale Growth at 900 °C for a Ni- and Cr-Free Co-Base Model Alloy with γ/γ’-Microstructure: Synergistic Effects by Combining Shot-Peening and Halogenation

2021 ◽  
Author(s):  
S. P. Hagen ◽  
K. Beck ◽  
D. Kubacka ◽  
H.-E. Zschau ◽  
M. C. Galetz ◽  
...  
Keyword(s):  
Oxidation Resistance ◽  
Shot Peening ◽  
Synergistic Effects ◽  
Microscopic Analysis ◽  
Alumina Scale ◽  
Model Alloy ◽  
Gravimetric Analysis ◽  
Scale Growth ◽  
Electron Microscopic ◽  
The Impact

AbstractThe oxidation resistance of novel γ/γ’-strengthened Co-base superalloys is clearly outmatched by their Ni-base counterparts within the high-temperature regime. Therefore, surface modification strategies to foster protective alumina growth seem auspicious. This study elucidates the impact of fluorination and shot-peening on protective alumina formation at 900 °C for a quaternary Co-base model alloy (Co-Al-W-Ta system) which is well known for an exceptionally low inherent oxidation resistance. Time-resolved isothermal gravimetric analysis (TGA) in synthetic air, detailed electron microscopic analysis, and X-ray diffraction (XRD) were used. For polished samples, no pronounced enhancement of oxidation resistance could be obtained by halogenation. However, in case of shot-peened samples (halogen-free), an increased tendency for alumina formation is found compared to polished surfaces. The very early stages of oxidation were identified to be especially crucial with respect to sustainable protective scale growth. Most noteworthy is the observation of a strong synergistic effect derived by a combination of halogenation and shot-peening, leading to significantly increased oxidation resistance.

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