Creep Deformation of Ultrafine Grained Ni7 5B1 7Si8

1985 ◽  
Vol 58 ◽  
Author(s):  
Gilles Nussbaum ◽  
Dieter G. Ast
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Creep Deformation ◽  
Stress Regime ◽  
Fine Grained ◽  
Self Diffusion ◽  
Diffusion Controlled ◽  
Superplastic Alloy ◽  
Ultrafine Grained ◽  
Applied Stresses

ABSTRACTThe creep behavior of the fine grained, intermetallic superplastic alloy of overall composition Ni7 5 B1 7Si8 prepared by crystallizing an amorphous precursor was studied in the temperature range between 500 and 615°C, the stress range between 36 and 800 MPa, and for grain sizes between 6.8 and 1.12*10−5 mm. The strain rates measured varied between 10−7 and 6*10−5 sec−1.Two different creep deformation mechanisms were observed. At low applied stresses, the material deformed in a diffusion controlled mode, with proportional to σ1. No dislocations developed in the grains, and the activation energy for creep was 4 eV. This value is higher than the self-diffusion of Ni in Ni (the principal constituent in the alloy) in agreement with observation in other Ni based alloy systems. At high applied stresses, a second mechanism became rate limiting. The activation energy of this process is about 0.6 eV and dislocations develop in the interior of grains when this mechanism operates.The transition between the two regimes is grain size and temperature dependent and occurs at about 400 MPa at a deformation temperature of 550°C and a grain size of 6.8 10−5 mm. An analysis of the grain size dependence of creep strain rate as well as its absolute value indicates that the low stress regime is Coble type creep.

Annealing Behavior during Heating Rate of Ultrafine-Grained 5052 Al Alloy deformed at Cryogenic Temperature

2007 ◽  
Vol 558-559 ◽  
pp. 735-740
Author(s):  
Ui Gu Gang ◽  
Dae Bum Park ◽  
Won Jong Nam
Keyword(s):  
Activation Energy ◽  
Heating Rate ◽  
Annealing Temperature ◽  
Al Alloy ◽  
Annealing Behavior ◽  
Self Diffusion ◽  
Diffusion Controlled ◽  
Ultrafine Grained ◽  
Grain Size Distributions ◽  
Higher Temperature

The microstructural evolution during thermal annealing of a cryogenic rolled 5052 Al alloy was investigated. The activation energy for annealing behavior was calculated using DSC data. For the heating rate of 16°C/min, the precipitation occurred at the annealing temperature of 150~230°C due to Mg self diffusion, recovery occurred at the annealing temperature of 230~260°C, and recrystallization proceeded at a higher temperature up to about 370°C. Both recovery and recrystallization gave rise to non-uniform, bimodal grain-size distributions, which may result from heterogeneous nanostructures. In addition, the activation energy for the precipitation was found as ~115kJ/mol, indicating the process was diffusion-controlled (Mg in Al), and the activation energy for recovery was found to be ~140kJ/mol, representing self-diffusion in pure Al.

Thermal Stability of Ultrafine-Grained Pure Titanium Processed by High-Pressure Torsion

2021 ◽  
Vol 1016 ◽  
pp. 338-344
Author(s):  
Wan Ji Chen ◽  
Jie Xu ◽  
De Tong Liu ◽  
De Bin Shan ◽  
Bin Guo ◽  
...  
Keyword(s):  
Activation Energy ◽  
Thermal Stability ◽  
Grain Size ◽  
High Pressure ◽  
Annealing Temperature ◽  
High Pressure Torsion ◽  
Stored Energy ◽  
Ultrafine Grained ◽  
Average Grain Size ◽  
Thermal Stability Of

High-pressure torsion (HPT) was conducted under 6.0 GPa on commercial purity titanium up to 10 turns. An ultrafine-grained (UFG) pure Ti with an average grain size of ~96 nm was obtained. The thermal properties of these samples were studied by using differential scanning calorimeter (DSC) which allowed the quantitative determination of the evolution of stored energy, the recrystallization temperatures, the activation energy involved in the recrystallization of the material and the evolution of the recrystallized fraction with temperature. The results show that the stored energy increases, beyond which the stored energy seems to level off to a saturated value with increase of HPT up to 5 turns. An average activation energy of about 101 kJ/mol for the recrystallization of 5 turns samples was determined. Also, the thermal stability of the grains of the 5 turns samples with subsequent heat treatments were investigated by microstructural analysis and Vickers microhardness measurements. It is shown that the average grain size remains below 246 nm when the annealing temperature is below 500 °C, and the size of the grains increases significantly for samples at the annealing temperature of 600 °C.

Effect of Silver on Superplastic Deformation in YBa2Cu3O7–x/Ag Composites

2002 ◽  
Vol 17 (5) ◽  
pp. 1172-1177
Author(s):  
Jondo Yun ◽  
Ye T. Chou ◽  
Martin P. Harmer
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Superplastic Deformation ◽  
Close Agreement ◽  
Silver Content ◽  
Strain Rates ◽  
Compression Tests ◽  
Fine Grained ◽  
Soft Inclusion ◽  
Activation Energy Of Deformation

Superplastic deformation was studied in fine-grained (0.7–1.1 μm) YBa2Cu3O7–x/Ag composites containing 2.5–25 vol% Ag. The compression tests were conducted in the temperature range of 750–875 °C and at strain rates of 10−5 to 10−3/s. For the YBa2Cu3O7−x/25%Ag composites with grain size of 0.7–1.1 μm, deformed at 800–850 °C and 10−5 to 10−3/s, the stress exponent, grain size exponent, and the activation energy of deformation were 2.0 ± 0.1, 2.5 ± 0.7, and 760 ± 100 kJ/mol, respectively. These values were the same as those of the pure YBa2Cu3O7−x, indicating that the deformation of the composite was controlled by that of the rigid YBa2Cu3O7−x phase. However, the strain rate was increased by the addition of silver as explained by the soft inclusion model of Chen. The dependence of the flow stress on the silver content was in close agreement with the prediction of the model.

Grain Refinement of Copper Alloys by Equal Channel Angular Pressing

2004 ◽  
Vol 449-452 ◽  
pp. 177-180 ◽  
Author(s):  
Cha Yong Lim ◽  
Jae Hyuck Jung ◽  
Seung Zeon Han
Keyword(s):  
Grain Size ◽  
Equal Channel Angular Pressing ◽  
Copper Alloys ◽  
Metallic Materials ◽  
Fine Grained ◽  
Angular Pressing ◽  
Fine Grain ◽  
Transmission Electron ◽  
Ultrafine Grained ◽  
Average Grain Size

The equal channel angular pressing (ECAP) is one of the methods to refine the grain size of metallic materials. This study investigates the effect of ECAP process on the formation of the fine grain size in oxygen free Cu and Cu alloys. The average grain size has been refined from 150 µm before ECAP to 300 nm. Microstructure was analyzed by transmission electron micrography (TEM). The diffraction pattern of the selected area confirmed the formation of ultrafine-grained structure with high angle grain boundaries after 8 cycles of ECAP. Mechanical properties such as microhardness and tensile properties of the ultra-fine grained copper materials have been investigated.

Effects of Temperature and Grain Size on Diffusivity of Aluminium: Electromigration Experiment and Molecular Dynamic Simulation

2022 ◽  
Author(s):  
Zhen Cui ◽  
Yaqian Zhang ◽  
Dong Hu ◽  
Sten Vollebregt ◽  
Jiajie Fan ◽  
...  
Keyword(s):  
Grain Size ◽  
Molecular Dynamic ◽  
Effective Diffusivity ◽  
Md Simulations ◽  
Atomic Diffusion ◽  
Polycrystalline Aluminum ◽  
Metallic Material ◽  
Self Diffusion ◽  
Diffusion Controlled ◽  
Increasing Temperature

Abstract Understanding the atomic diffusion features in metallic material is significant to explain the diffusion-controlled physical processes. In this paper, using electromigration experiments and molecular dynamic (MD) simulations, we investigate the effects of grain size and temperature on the self-diffusion of polycrystalline aluminum (Al). The mass transport due to electromigration are accelerated by increasing temperature and decreasing grain size. Magnitudes of effective diffusivity (Deff) and grain boundary diffusivity (DGBs) are experimentally determined, in which the Deff changes as a function of grain size and temperature, but DGBs is independent of the grain size, only affected by the temperature. Moreover, MD simulations of atomic diffusion in polycrystalline Al demonstrate those observations from experiments. Based on MD results, the Arrhenius equation of DGBs and empirical formula of the thickness of grain boundaries at various temperatures are obtained. In total, Deff and DGBs obtained in the present study agree with literature results, and a comprehensive result of diffusivities related to the grain size is presented.

Elevated temperature deformation of fine-grained La0.9Sr0.1MnO3

1996 ◽  
Vol 11 (3) ◽  
pp. 657-662 ◽  
Author(s):  
J. Wolfenstine ◽  
T. R. Armstrong ◽  
W. J. Weber ◽  
M. A. Boling-Risser ◽  
K. C. Goretta ◽  
...  
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Elevated Temperature ◽  
Perovskite Oxides ◽  
Lattice Diffusion ◽  
Diffusional Creep ◽  
Temperature Deformation ◽  
Creep Data ◽  
Fine Grained ◽  
Fine Grain

Compressive creep behavior of fine-grained (5 μm) La0.9Sr0.1MnO3with a relative theoretical density between 85 and 90% was investigated over the temperature range 1150–1300 °C in air. The fine grain size, brief creep transients, stress exponent close to unity, and absence of deformation-induced dislocations, suggested that the deformation was controlled by a diffusional creep mechanism. The activation energy for creep of La0.9Sr0.1MnO3was 490 kJ/mole. A comparison of the activation energy for creep of La0.9Sr0.1MnO3with existing diffusion and creep data for perovskite oxides suggested that the diffusional creep of La0.9Sr0.1MnO3was controlled by lattice diffusion of the cations, either lanthanum or manganese.

Creep behavior of a cryomilled ultrafine-grained Al–4% Mg alloy

2000 ◽  
Vol 15 (10) ◽  
pp. 2215-2222 ◽  
Author(s):  
R. W. Hayes ◽  
V. Tellkamp ◽  
E. J. Lavernia
Keyword(s):  
Activation Energy ◽  
Thermal Stability ◽  
Grain Size ◽  
Grain Boundary ◽  
Creep Behavior ◽  
Boundary Region ◽  
Mg Alloy ◽  
Pinning Force ◽  
Ultrafine Grained ◽  
Boundary Deformation

The creep behavior of a cryomilled ultrafine-grained Al–Mg alloy was examined. The grain size ranged from 300 to 400 nm. The stress exponents ranged from 7.2 to 7.4. The apparent activation energy for creep, 83.7 kJ/mol at 27.5 MPa and 77 kJ/mol at 38 MPa, agreed well with the activation energy for grain boundary diffusion in aluminum. Transmission electron microscope analysis following creep at 300 °C to approximately 0.2% strain in 1411 h revealed the grain size was unchanged from its as-extruded size indicating significant thermal stability of this material at relatively high fractions of the melting temperature. The creep resistance of the Al–Mg alloy was rationalized in terms of an attractive interaction between grain boundary dislocations and incoherent particles within the boundary region, which suppressed grain boundary deformation. The grain boundary particles also led to high thermal stability by exerting a Zener pinning force on the grain boundaries, thus inhibiting grain growth at high temperatures.

Mechanical Properties of Ultra-Fine Grained Al-Li Alloys

2006 ◽  
Vol 513 ◽  
pp. 25-34 ◽  
Author(s):  
Bogusława Adamczyk-Cieślak ◽  
Małgorzata Lewandowska ◽  
Jaroslaw Mizera ◽  
Krzysztof Jan Kurzydlowski
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Equal Channel Angular Extrusion ◽  
Coarse Grain ◽  
Initial State ◽  
Fine Grained ◽  
Compression Deformation ◽  
Ultrafine Grained ◽  
Yield Stress Increase ◽  
Li Content

The results obtained in the present study reveal the effect of equal channel angular extrusion (ECAE) on the grain size and mechanical properties of Al-Li alloys. During 8 passes of ECAE process, coarse grain microstructure in the initial state transforms into ultrafine grained. The final grain size depends on both total strain applied and Li content in the alloy. Due to the grain refinement the microhardness and yield stress increase by 100%. During compression deformation, the coarse grain alloys exhibit continuous hardening, whereas in the ultrafine-grained alloys, a stagnation of work hardening at the beginning of compression deformation is observed. This behaviour is related to the dynamic recovery of the severely deformed microstructure.

Influence of the Initial Grain Size on the Structural-Phase State of the VT20 Titanium Alloy Surface after Implantation

2021 ◽  
Vol 1037 ◽  
pp. 535-540
Author(s):  
Viktor Vasilevich Ovchinnikov ◽  
Irina Aleksandrovna Kurbatova ◽  
Elena Vladimirovna Luk'yanenko ◽  
Nadezda Vladimirovna Uchevatkina ◽  
Svetlana Viktorovna Yakutina
Keyword(s):  
Grain Size ◽  
Titanium Alloy ◽  
Phase State ◽  
Structural Phase ◽  
Alloy Surface ◽  
Structural Phase State ◽  
Fine Grained ◽  
Ultrafine Grained ◽  
Alloy Vt20 ◽  
Vt20 Titanium Alloy

The article presents the results of studies of titanium alloy VT20 in ultrafine-grained (UFG), subfine-grained (SMG), fine-grained (MZ) and mesopolycrystalline (MPC) states, obtained, including by methods of plastic deformation and subsequently subjected to ion implantation. The effect of grain size on the structural-phase state of the titanium alloy surface and mechanical properties is shown.

scholarly journals Submarine lava deltas of the 2018 eruption of Kīlauea volcano

2021 ◽  
Vol 83 (4) ◽  
Author(s):  
S. Adam Soule ◽  
Michael Zoeller ◽  
Carolyn Parcheta
Keyword(s):  
Grain Size ◽  
Pore Pressure ◽  
Mechanistic Model ◽  
Large Fraction ◽  
Volcanic Hazards ◽  
Lava Flows ◽  
Coarse Grained ◽  
Fine Grained ◽  
Fine Grain ◽  
Delta Formation

AbstractHawaiian and other ocean island lava flows that reach the coastline can deposit significant volumes of lava in submarine deltas. The catastrophic collapse of these deltas represents one of the most significant, but least predictable, volcanic hazards at ocean islands. The volume of lava deposited below sea level in delta-forming eruptions and the mechanisms of delta construction and destruction are rarely documented. Here, we report on bathymetric surveys and ROV observations following the Kīlauea 2018 eruption that, along with a comparison to the deltas formed at Pu‘u ‘Ō‘ō over the past decade, provide new insight into delta formation. Bathymetric differencing reveals that the 2018 deltas contain more than half of the total volume of lava erupted. In addition, we find that the 2018 deltas are comprised largely of coarse-grained volcanic breccias and intact lava flows, which contrast with those at Pu‘u ‘Ō‘ō that contain a large fraction of fine-grained hyaloclastite. We attribute this difference to less efficient fragmentation of the 2018 ‘a‘ā flows leading to fragmentation by collapse rather than hydrovolcanic explosion. We suggest a mechanistic model where the characteristic grain size influences the form and stability of the delta with fine grain size deltas (Pu‘u ‘Ō‘ō) experiencing larger landslides with greater run-out supported by increased pore pressure and with coarse grain size deltas (Kīlauea 2018) experiencing smaller landslides that quickly stop as the pore pressure rapidly dissipates. This difference, if validated for other lava deltas, would provide a means to assess potential delta stability in future eruptions.

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