Creep Behavior of an Oxide Dispersion Strengthened Iron with Ultrafine Grain Structure

2010 ◽  
Vol 638-642 ◽  
pp. 3194-3199
Author(s):  
Valeriy Dudko ◽  
Rustam Kaibyshev ◽  
Andrey Belyakov ◽  
Yoshikazu Sakai ◽  
Kaneaki Tsuzaki
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Deformation Behavior ◽  
Oxide Dispersion Strengthened ◽  
Lattice Diffusion ◽  
Grain Structure ◽  
Ultrafine Grain ◽  
Creep Data ◽  
Temperature Range

The creep behavior of oxide-bearing Fe-0.6%O steel was studied in the temperature range of 550-700°C at stresses ranging from 100 to 400 MPa. The creep data showed high values of an apparent stress exponent n close to 16 for power-law creep. In addition the apparent experimental activation energy was much higher than that for the lattice diffusion in -iron. Analysis of creep data revealed that the deformation behavior was strongly affected by the threshold stresses, which are associated with the interaction between moving dislocations and fine incoherent oxide particles. Analysis of deformation behavior in terms of threshold stress leads the true stress exponent of 8; the activation energy for creep became close to value of activation energy for lattice diffusion at 700°C and for pipe-diffusion in the temperature range of 550–650°C.

Grain Refinement and Deformation Behavior of Ultrafine Grained Pd and Pd-Ag Alloys Produced by HPT

2008 ◽  
Vol 584-586 ◽  
pp. 182-187
Author(s):  
Lilia Kurmanaeva ◽  
Yulia Ivanisenko ◽  
J. Markmann ◽  
Ruslan Valiev ◽  
Hans Jorg Fecht
Keyword(s):  
Mechanical Properties ◽  
Deformation Behavior ◽  
Materials Science ◽  
High Pressure Torsion ◽  
Uniform Elongation ◽  
Grain Structure ◽  
Coarse Grained ◽  
Ultrafine Grain ◽  
Ultrafine Grained ◽  
Ultrafine Grain Structure

Investigations of mechanical properties of nanocrystalline (nc) materials are still in interest of materials science, because they offer wide application as structural materials thanks to their outstanding mechanical properties. NC materials demonstrate superior hardness and strength as compared with their coarse grained counterparts, but very often they possess a limited ductility or show low uniform elongation due to poor strain hardening ability. Here, we present the results of investigation of the microstructure and mechanical properties of nc Pd and Pd-x%Ag (x=20, 60) alloys. The initially coarse grained Pd-x% Ag samples were processed by high pressure torsion, which resulted in formation of homogenous ultrafine grain structure. The increase of Ag contents led to the decrease of the resulted grain size and change in deformation behavior, because of decreasing of stacking fault energy (SFE). The samples with larger Ag contents demonstrated the higher values of hardness, yield stress and ultimate stress. Remarkably the uniform elongation had also increased with increase of strength.

Microstructures and Creep of AM50-Sb-Gd Alloys

2005 ◽  
Vol 488-489 ◽  
pp. 749-752 ◽  
Author(s):  
Su Gui Tian ◽  
Keun Yong Sohn ◽  
Hyun Gap Cho ◽  
Kyung Hyun Kim
Keyword(s):  
Activation Energy ◽  
Creep Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Deformation Mechanism ◽  
Creep Resistance ◽  
Fine Particles ◽  
Dislocation Climb ◽  
The Matrix

Creep behavior of AM50-0.4% Sb-0.9%Gd alloy has been studied at temperatures ranging from 150 to 200°C and at stresses ranging from 40 to 90 MPa. Results show that the creep rate of AM50-0.4%Sb-0.9%Gd alloy was mainly controlled by dislocation climb at low stresses under 50 MPa. The activation energy for the creep was 131.2 ± 10 kJ/mol and the stress exponent was in the range from 4 to 9 depending on the applied stress. More than one deformation-mechanism were involved during the creep of this alloy. Microstructures of the alloy consist of a–Mg matrix and fine particles, distinguished as Mg17Al12, Sb2Mg3, and Mg2Gd or Al7GdMn5 that were homogeneously distributed in the matrix of the alloy, which effectively reduced the movement of dislocations, enhancing the creep resistance. Many dislocations were identified to be present on non-basal planes after creep deformation.

Interface Controlled Diffusional Creep of Cu + 2.8 at.% Co Solid Solution

2012 ◽  
Vol 322 ◽  
pp. 33-39 ◽  
Author(s):  
Sergei Zhevnenko ◽  
Eugene Gershman
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
Surface Tension ◽  
High Temperature ◽  
Creep Behavior ◽  
Pure Copper ◽  
Diffusional Creep ◽  
High Temperature Creep ◽  
Temperature Range ◽  
Different Temperatures

High-temperature creep experiments were performed on a Cu-2.8 ат.% Co solid solution. Cylindrical foils of 18 micrometers thickness were used for this purpose. Creep tests were performed in a hydrogen atmosphere in the temperature range of about from 1233 K to 1343 K and at stresses lower than 0.25 MPa. For comparison, a foil of pure copper and Cu-20 at.% Ni solid solution were investigated on high temperature creep. Measurements on the Cu foil showed classical diffusional creep behavior. The activation energy of creep was defined and turned out to be equal 203 kJ/mol, which is close to the activation energy of bulk self-diffusion of copper. There was a significant increase in activation energy for the Cu-20 at.% Ni solid solution. Its activation energy was about 273 kJ/mol. The creep behavior of Cu-Co solid solution was more complicated. There were two stages of diffusional creep at different temperatures. The extremely large activation energy (about 480 kJ/mol) was determined at relatively low temperature and a small activation energy (about 105 kJ/mol) was found at high temperatures. The creep rate of Cu-Co solid solution was lower than that of pure copper at all temperatures. In addition, the free surface tension of Cu-2.8 ат.% Co was measured at different temperatures from 1242 K to 1352 K. The surface tension increases in this temperature range from 1.6 N/m to 1.75 N/m. There were no features on the temperature dependence of the surface tension.

scholarly journals Microstructure and impression creep characteristics Al-9Si-xCu aluminum alloys

10.30544/101 ◽  
2015 ◽  
Vol 21 (2) ◽  
pp. 115-126 ◽  
Author(s):  
Mohsen Yousefi ◽  
Mehdi Dehnavi ◽  
S.M. Miresmaeili
Keyword(s):  
Activation Energy ◽  
Aluminum Alloys ◽  
Intermetallic Compound ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Eutectic Phase ◽  
Dislocation Creep ◽  
Impression Creep ◽  
Pipe Diffusion ◽  
Creep Characteristics

The effects of 1.5, 2.5 and 3.5 wt.% Cu additions on the microstructure and creep behavior of the as-cast Al-9Si alloy were investigated by impression tests. The tests were performed at temperature ranging from 493 to 553 K and under punching stresses in the range 300 to 414 MPa for dwell times up to 3000 seconds. The results showed that, for all loads and temperatures, the Al–9Si–3.5Cu alloy had the lowest creep rates and thus, the highest creep resistance among all materials tested. This is attributed to the formation of hard intermetallic compound of Al2Cu, and higher amount of α-Al2Cu eutectic phase. The stress exponent and activation energy are in the ranges of 5.2- 7.2 and 115 -150 kJ/ mol, respectively for all alloys. According to the stress exponent and creep activation energies, the lattice and pipe diffusion- climb controlled dislocation creep were the dominant creep mechanism.

Comparison of the High-Temperature Deformation of Alumina-Zirconia and Alumina-Zirconia-Mullite Composites

2005 ◽  
Vol 20 (1) ◽  
pp. 13-17 ◽  
Author(s):  
Tiandan Chen ◽  
Martha L. Mecartney
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
Strain Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Reactive Processing ◽  
Lower Activation ◽  
Lower Activation Energy

An alumina-based ceramic codispersed with 15 vol% zirconia and 15 vol% mullite (AZM) was synthesized by reactive processing, and the creep behavior was compared to alumina with 30 vol% zirconia (AZ). Constant stress compressive creep behavior for AZM exhibited a stress exponent of 2 and an activation energy of 770 KJ/mol, while a similar stress exponent but lower activation energy of 660 KJ/mol was found for AZ. The strain rate of AZM, however, was more than twice that of the AZ under the same deformation conditions, indicating a better potential for superplastic shape forming.

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.

Hot Deformation Behavior and Microstructure Evolution of Ti-6.5Al-1.5Zr-3.5Mo-0.3Si with an Equiaxed α+β Starting Structure

2007 ◽  
Vol 546-549 ◽  
pp. 1383-1388 ◽  
Author(s):  
Hui Qin Chen ◽  
Hao Zhuan Lin ◽  
L. Guo ◽  
Chun Xiao Cao
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Phase Field ◽  
Hot Deformation ◽  
Deformation Behavior ◽  
Hot Deformation Behavior ◽  
Temperature Range ◽  
Self Diffusion ◽  
Β Phase ◽  
Plastic Deformation Behavior

The hot deformation behavior of TC11 with an equiaxed α+β pre-form microstructure was investigated by hot compression tests in the temperature range 800°C–1090°C and strain rate range 1×10-310s-1. Several approaches have been used in this investigation, which include analysis of shapes of stress–strain curves, kinetic analysis and microstructure observation. The experimented results showed that, (1) In the β phase field, the alloy exhibits dynamic re-crystallization. The apparent activation energy in this domain is estimated to be 183kJ/ mol, which is close to that for self-diffusion in β. The re-crystallized grain size may be governed by competing of diffusion and dynamic re-crystallization rate at deforming conditions. (2) In the α+β phase field, the alloy exhibits super-plastic deformation behavior at 0.001-0.01s-1 and 980°C -850°C, and the apparent activation energy estimated in this domain is about 600 kJ/mol, which is much higher than that for self-diffusion in α-titanium due to β volume fraction is not constant over the test temperature range.

Elevated temperature mechanical behavior of CoSi and particulate reinforced CoSi produced by spray atomization and co-deposition

1994 ◽  
Vol 9 (2) ◽  
pp. 362-371 ◽  
Author(s):  
Don Baskin ◽  
Jeff Wolfenstine ◽  
Enrique J. Lavernia
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Elevated Temperature ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Diffusional Creep ◽  
Spray Atomization ◽  
Dislocation Glide ◽  
Unreinforced Material ◽  
Particulate Reinforced

Monolithic CoSi and TiB2 reinforced CoSi materials were produced by spray atomization and co-deposition. The creep behavior of both materials at elevated temperature was investigated. The unreinforced material of grain size ≍25 μm exhibited a stress exponent of three, activation energy for creep of 320 kJ/mole, dislocation substructure of homogeneously distributed dislocations, and inverse creep transients upon stress increases. These results suggest that the creep behavior of CoSi is controlled by a dislocation glide mechanism. In contrast, the reinforced material of a finer grain size (≍10 μm) exhibited a stress exponent of unity, activation energy for creep of 240 kJ/mole, and negligible creep transients upon stress increases, suggesting that the creep behavior of the reinforced material is controlled by a diffusional creep mechanism. The creep resistance of the reinforced material was lower than that for the unreinforced material. This is a result of the finer grain size and higher porosity in the reinforced material.

Investigation on Creep Mechanisms of Alloy 709

2017 ◽  
Author(s):  
Abdullah S. Alomari ◽  
Nilesh Kumar ◽  
Korukonda L. Murty
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Tensile Tests ◽  
Lattice Diffusion ◽  
Creep Tests ◽  
True Activation Energy ◽  
Sodium Fast Reactor ◽  
Safety And Reliability ◽  
Power Law Creep ◽  
Gen Iv

To improve efficiency, safety, and reliability of nuclear reactors, structural materials for Gen-IV reactors are being designed and developed. Alloy 709, a 20Cr-25Ni austenitic stainless steel, has superior mechanical properties to be a preferred candidate material for Sodium Fast Reactor structural application. Creep tensile tests were performed at temperatures of 700 °C, 725 °C and 750 °C and range of stresses from 100 MPa to 250 MPa. The apparent stress exponent and activation energy were found to be 10.3±0.4 and 368.6±14.7 kJ/mol. Linear extrapolation method was used to rationalize the higher stress exponent and activation energy relative to the mechanism in power law creep yielding to a true stress exponent of 7.1 ± 0.3 and a true activation energy of 277 ± 12.8 kJ/mol which is close to the lattice diffusion of iron in Fe-20Cr-25Ni. Hence, the lattice diffusion controlled dislocation climb process is believed to be the rate controlling creep deformation mechanism in this range of stresses and temperatures. The appropriate constitutive equation was developed based on the results; however, microstructural evaluations are under investigation to confirm the rate controlling mechanism. In addition, creep tests at higher temperatures and lower stresses are being conducted to extend the stress and strain-rate ranges to observe possible transition in creep mechanism.

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