Enhanced Plasticity of Pure Nickel Processed by HPT Consolidation of Rapid Quenched Ribbons

2016 ◽  
Vol 838-839 ◽  
pp. 122-126
Author(s):  
Alexander P. Zhilyaev
Keyword(s):  
Liquid Phase ◽  
Low Temperature ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Nanocrystalline Materials ◽  
Pure Nickel ◽  
Superplastic Behavior ◽  
Half Century ◽  
Pure Metals ◽  
Future Work

Although superplasticity has intensively been studied for half century, few observations have been reported for pure metals due to fast grain growth at temperatures required for superplasticity. With developing of nanocrystalline materials, there was a hope that superplasticity could be obtained in a number of pure metals. Indeed, low temperature superplasticity in pure nickel was reported in pioneering work in 1999, later superplastic feature of nanonickel was attributed to sulfur presence in grain boundaries. Recently, it was concluded that superplasticity it is not related to the presence of sulfur at grain boundaries or a liquid phase at grain boundaries. Thereby, the phenomenon of superplasticity in pure metals is still far away for our understanding and it requires future work. This report is devoted to reassessment of superplastic behavior of nanonickel and it provides new results on enhanced plasticity of pure nickel processed by HPT consolidation of rapid quenched ribbons.

Grain growth behavior of a nanostructured 5083 Al–Mg alloy

2001 ◽  
Vol 16 (4) ◽  
pp. 938-944 ◽  
Author(s):  
V. L. Tellkamp ◽  
S. Dallek ◽  
D. Cheng ◽  
E. J. Lavernia
Keyword(s):  
Activation Energy ◽  
Stress Relaxation ◽  
Low Temperature ◽  
Grain Boundaries ◽  
Relaxation Process ◽  
Grain Growth ◽  
Alloy Powder ◽  
Growth Behavior ◽  
Mg Alloy ◽  
Grain Growth Behavior

A nanostructured 5083 Al–Mg alloy powder was subjected to various thermal heat treatments in an attempt to understand the fundamental mechanisms of recovery, recrystallization and grain growth as they apply to nanostructured materials. A low-temperature stress relaxation process associated with reordering of the grain boundaries was found to occur at 158 °C. A bimodal restructuring of the grains occurred at 307 °C for the unconstrained grains and 381 °C for the constrained grains. An approximate activation energy of 5.6 kJ/mol was found for the metastable nanostructured grains, while an approximate activation energy of 142 kJ/mol was found above the restructuring temperature.

Grain growth and the microstructural effects on the properties of YBa2Cu3O7−y superconductor

1990 ◽  
Vol 5 (9) ◽  
pp. 1819-1826 ◽  
Author(s):  
C. T. Chu ◽  
B. Dunn
Keyword(s):  
Liquid Phase ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Tetragonal Phase ◽  
Sintering Temperature ◽  
Oxygen Stoichiometry ◽  
Microstructural Development ◽  
Prolonged Annealing ◽  
Microstructural Effects ◽  
Oxygenation Rate

The microstructural development and grain growth of YBa2Cu3O7−y ceramics at 925, 950, and 975 °C were studied. Densification occurred quite rapidly at temperatures below 925 °C. The grain growth of YBa2Cu3O7−y followed a D5 − D50 = Kt relation when sintered at 925 and 950 °C. At 975 °C, the kinetics changed to cubic (D3) behavior, which can be attributed to the formation of a liquid phase at grain boundaries. A trend of decreasing Jc with increasing sintering temperature was observed. Other properties including Tc and the width of the transition were virtually unaffected by the change in microstructure. Without prolonged annealing, a relatively homogeneous oxygen stoichiometry of 6.8 was obtained for fairly dense samples (>93% of theoretical). These results suggest that the oxygenation rate of YBa2Cu3O7−y was quite rapid between the tetragonal phase and the orthorhombic composition of YBa2Cu3O6.8.

scholarly journals Low-Temperature Sintering of Apatite-Type Lanthanum Silicate with Fluoride Additives

2010 ◽  
Vol 62 ◽  
pp. 235-240
Author(s):  
Junichi Takahashi ◽  
Hidetoshi Honda ◽  
Takaya Akashi ◽  
Kazutomo Abe ◽  
Hidenobu Itoh ◽  
...  
Keyword(s):  
Activation Energy ◽  
Liquid Phase ◽  
Low Temperature ◽  
Bulk Density ◽  
Grain Growth ◽  
Low Temperatures ◽  
Abnormal Grain Growth ◽  
Low Temperature Sintering ◽  
Lanthanum Silicate ◽  
Apatite Type

Various fluorides (3 - 8 wt%) were added to a La9.33Si6O26 (LSO) powder synthesized by calcining the corresponding oxides mixture at 1100°C for 4 h. The addition of BaF2, AlF3 or Ba3Al2F12 caused an appreciable and substantial increase in bulk density after sintering at 1400º and 1450°C, respectively. These fluorides melt below 1400°C to form liquid phase which could assist the densification at low temperatures. Abnormal grain growth was observed for LSO samples with the addition of AlF3 and Ba3Al2F12, but it was effectively suppressed by stepwise sintering at 1400º and 1450°C. The BaF2 addition brought about the simultaneous promotion of densification and moderate grain growth, leading to the production of a densified LSO sample showing a conductivity of 1.5 x 10–2 Scm–1 at 800°C with an activation energy of 1.23 eV.

Low-temperature sintering of PNW–PMN–PZT piezoelectric ceramics

2007 ◽  
Vol 22 (9) ◽  
pp. 2410-2415 ◽  
Author(s):  
Pengxian Lu ◽  
Mankang Zhu ◽  
Dehe Xu ◽  
Wenjun Zou ◽  
Zhengxin Li ◽  
...  
Keyword(s):  
Low Temperature ◽  
Phase Boundary ◽  
Grain Boundaries ◽  
Relative Density ◽  
Grain Growth ◽  
Piezoelectric Properties ◽  
Sintering Temperature ◽  
Secondary Phase ◽  
Low Temperature Sintering ◽  
Densification Process

For low-temperature firing of Pb0.94Sr0.06(Ni1/2W1/2)0.02(Mn1/3Nb2/3)0.07(Zr0.51Ti0.49)0.91O3 (PNW–PMN–PZT) system, BiFeO3 is selected as the sintering agent. In this study, the effects of BiFeO3 addition and sintering temperature on the microstructures and piezoelectric properties of the ceramics were investigated in detail. The ceramic with 10 mol% BiFeO3 sintered at 950 °C possesses optimal microstructure and piezoelectric properties. However, with the increase of sintering temperature the lower relative density, abnormal grain growth, and secondary phase accumulated at grain boundaries are observed, which deteriorates the piezoelectric properties. For the ceramics with different BiFeO3 addition sintered at 950 °C, the densification process and the grain growth are improved by suitable BiFeO3, while the morphotropic phase boundary (MPB) moving to the Ti-rich direction and the shrinkage of crystal cell occur. However, extra BiFeO3 inhabits the grain growth and introduces more cavities into the materials. Because of the microstructural changes that accompany the addition of BiFeO3 and the resulting decrease in sintering temperature, the maximum values of the piezoelectric properties are attained. By doping with 10 mol% BiFeO3, the sintering temperature of the PNW–PMN–PZT system can be lowered successfully from 1200 to 950 °C, while the excellent electric properties are kept.

Crystalline Films on Amorphous Substrates by Zone Melting and Surface-Energy-Driven Grain Growth in Conjunction with Patferning

1985 ◽  
Vol 53 ◽  
Author(s):  
Henry I. Smith ◽  
M. W. Geis ◽  
C. V. Thompson ◽  
C. K. Chen
Keyword(s):  
Low Temperature ◽  
Surface Energy ◽  
Grain Boundaries ◽  
Grain Growth ◽  
High Temperatures ◽  
Zone Melting ◽  
Si Substrates ◽  
Crystalline Films ◽  
Amorphous Substrates ◽  
Si Films

ABSTRACTTwo approaches to preparing oriented crystalline films on amorphous substrates are reviewed briefly: zone-melting recrystallization (ZMR) and surface-energy-driven grain growth (SEDGG). In both approaches patterning can be employed either to establish orientation or to control the location of defects. ZMR has been highly successful for the growth of Si films on oxidized Si substrates, but its applicability is limited by the high temperatures required. SEDGG has been investigated as a potentially universal, low temperature approach. It has been demonstrated in Si, Ge, and Au. Surface gratings favor the growth of grains with a specific in-plane orientation. In order for SEDGG to be of broad practical value, the mobility of semiconductor grain boundaries must be increased substantially. Mobility enhancement has been achieved via doping and ion bombardment.

Triple Junction Controlled Grain Growth

2004 ◽  
Vol 467-470 ◽  
pp. 1093-1098 ◽  
Author(s):  
Vladimir Yu. Novikov
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Growth Kinetics ◽  
Triple Junction ◽  
Nanocrystalline Materials ◽  
Triple Junctions ◽  
Restricted Mobility ◽  
Triple Junction Mobility ◽  
Grain Diameter

Grain growth in 2D polycrystals was simulated under the supposition that triple junctions possess a restricted mobility and so impede the migration of grain boundaries. A parameter 0 L = 0 D m taking into account the effect of triple junctions was varied in the range from 0.003 to 270 (m is the ratio of the triple junction mobility to that of grain boundary and 0 D the initial grain diameter). It was shown that at 0 L <0.4–0.5, i.e. at a small 0 D and small m, the growth kinetics becomes linear. It is supposed that the effect of triple junctions on grain growth can be observed in nanocrystalline materials.

Grain-Growth Phenomena in ZnO-Based Ceramics

2007 ◽  
Vol 558-559 ◽  
pp. 857-862 ◽  
Author(s):  
Slavko Bernik ◽  
Mateja Podlogar ◽  
Nina Daneu ◽  
Aleksander Rečnik
Keyword(s):  
Liquid Phase ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Growth Mechanism ◽  
Pyrochlore Phase ◽  
Early Stages ◽  
Zno Ceramics

Grain growth in ZnO ceramics doped with 0.01 and 0.02 mol.% Bi2O3 and Sb2O3 in amounts appropriate for Sb2O3/Bi2O3 ratios of 0.8, 1.0 and 1.2, sintered at 1200oC for 2 and 10 hours, was investigated. Grain growth is promoted by a sufficient amount of the Bi2O3 liquid phase at the grain boundaries and also by the presence of IBs in the ZnO grains. While the doping of ZnO with such small amounts of Bi2O3 caused the exaggerated growth of some grains, the addition of Sb2O3 resulted, via the IBs-induced grain-growth mechanism, in uniform grain growth and the presence of IBs in most of the ZnO grains. The formation of the pyrochlore phase bounds the Bi2O3 and Sb2O3, which affects, depending on the Sb2O3/Bi2O3 ratio, the occurrence of the Bi2O3 liquid phase and also the amount of available Sb2O3 for the nucleation of IBs in the ZnO grains during the early stages of sintering. As a result, it influences the grain growth.

Elucidation of block boundaries as the dissolution channels in hydrated cement

1978 ◽  
Vol 36 (1) ◽  
pp. 484-485
Author(s):  
N.V. Belov ◽  
U.I. Papiashwili ◽  
B.E. Yudovich
Keyword(s):  
Liquid Phase ◽  
Grain Boundaries ◽  
Benzoyl Peroxide ◽  
Phase Contrast ◽  
Active Role ◽  
Point Of View ◽  
Hardened Cement ◽  
Hydrated Cement ◽  
Hardened Cement Paste

It has been almost universally adopted that dissolution of solids proceeds with development of uniform, continuous frontiers of reaction.However this point of view is doubtful / 1 /. E.g. we have proved the active role of the block (grain) boundaries in the main phases of cement, these boundaries being the areas of hydrate phases' nucleation / 2 /. It has brought to the supposition that the dissolution frontier of cement particles in water is discrete. It seems also probable that the dissolution proceeds through the channels, which serve both for the liquid phase movement and for the drainage of the incongruant solution products. These channels can be appeared along the block boundaries.In order to demonsrate it, we have offered the method of phase-contrast impregnation of the hardened cement paste with the solution of methyl metacrylahe and benzoyl peroxide. The viscosity of this solution is equal to that of water.

HREM observation of NiO growth on submicron spheres of pure nickel

1989 ◽  
Vol 47 ◽  
pp. 548-549
Author(s):  
C.M. Teng ◽  
T.F. Kelly ◽  
J.P. Zhang ◽  
H.M. Lin ◽  
Y.W. Kim
Keyword(s):  
Nickel Oxide ◽  
Grain Boundaries ◽  
Pure Nickel ◽  
Submicron Particles ◽  
Crystal Formation ◽  
Nickel Wire ◽  
Liquid Droplets ◽  
Oxide Interface ◽  
Nickel Chromium ◽  
Chromium Alloys

Spherical submicron particles of materials produced by electrohydrodynamic (EHD) atomization have been used to study a variety of materials processes including nucleation of alternative crystallization phases in iron-nickel and nickel-chromium alloys, amorphous solidification in submicron droplets of pure metals, and quasi-crystal formation in nickel-chromium alloys. Some experiments on pure nickel, nickel oxide single crystals, the nickel/nickel(II) oxide interface, and grain boundaries in nickel monoxide have been performed by STEM. For these latter studies, HREM is the most direct approach to obtain particle crystal structures at the atomic level. Grain boundaries in nickel oxide have also been investigated by HREM. In this paper, we present preliminary results of HREM observations of NiO growth on submicron spheres of pure nickel.Small particles of pure nickel were prepared by EHD atomization. For the study of pure nickel, 0.5 mm diameter pure nickel wire (99.9975%) is sprayed directly in the EHD process. The liquid droplets solidify in free-flight through a vacuum chamber operated at about 10-7 torr.

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