Static and cyclic creep behavior of in situTiB2 particulate reinforced aluminum composite

1999 ◽  
Vol 14 (12) ◽  
pp. 4541-4550 ◽  
Author(s):  
Z. Y. Ma ◽  
S. C. Tjong ◽  
S. X. Li
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Cyclic Creep ◽  
Creep Tests ◽  
Aluminum Composite ◽  
Self Diffusion ◽  
True Activation Energy ◽  
Static Creep ◽  
Particulate Reinforced

Static and cyclic creep tests of Al–15 vol% TiB2in situ composite were carried out at 573–623 K. The values of apparent stress exponent and activation energy for cyclic creep of the composite were much higher than that for static creep. Furthermore, the cyclic creep rate tended to decrease with increasing percentage of unloading amount but was independent of the loading frequencies under the frequency ranges investigated. Finally, the true stress exponent of the composite was equal to 8, and the true activation energy was close to the value for the lattice self-diffusion of aluminum by incorporating a threshold stress for the analysis.

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.

The contribution of friction stress to the creep behaviour of the nickel-base in situ composite, γ—γ'-Cr 3 C 2

1980 ◽  
Vol 373 (1752) ◽  
pp. 93-109 ◽  
Keyword(s):  
Activation Energy ◽  
Creep Behaviour ◽  
Friction Stress ◽  
Matrix Alloy ◽  
Dislocation Motion ◽  
Self Diffusion ◽  
The Matrix ◽  
Nickel Base ◽  
Distribution Of Stress

Transient creep following stress reductions has been analysed by the method described by McLean (1980) to determine the friction stress σ 0 as a function of temperature and directional solidification conditions for the γ-γ'-Cr 3 Cr 2 in-situ composite and for the γ-γ' matrix alloy. These values of σ 0 are identical to the flow stresses at creep strain rates and can be identified with the sums of the barriers to dislocation motion through the matrix by climb around γ'-particles and Orowan bowing between the carbide fibres. The friction stress and the kinetics of deformation of the composite are determined by the matrix behaviour, whereas its creep strength depends on the distribution of stress between fibre and matrix. When the steady-state creep behaviour of γ-γ'-Cr 3 C 2 is analysed by using the usual power law description in terms of the effective stress σ — σ 0 , rather than the applied stress σ, the stress exponent is ca 4 and the activation energy is similar to the activation energy of self-diffusion for nickel. The results provide strong evidence for the operation of recovery-creep in both the composite and matrix alloys.

Impression Creep Behaviour of Extruded Mg-Sn Alloy

2016 ◽  
Vol 8 (3) ◽  
Author(s):  
V. Thenambika ◽  
S. Jayalakshmi ◽  
R.A. Singh ◽  
J.K. Nidhi ◽  
M. Gupta
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Creep Deformation ◽  
Creep Behaviour ◽  
Impression Creep ◽  
Temperature Dependent ◽  
Creep Tests ◽  
Automobile Engine ◽  
Creep Curves ◽  
Mg2sn Phase

Mg-Sn alloys contain thermally stable Mg2Sn phase, and are proposed as heat-resistant alloys for automobile engine applications. In this study, the creep behaviour of Mg-5Sn alloy was investigated using impression creep technique. The impression creep tests were carried out under constant punching stress in the range of 80-320 MPa at temperatures 373-573 K, for dwell times up to 5 hours. The results highlight that creep of Mg-5Sn alloy was load and temperature dependent, i.e. increasing the load and temperature resulted in larger creep deformation and hence to higher creep rates. From the creep curves, the stress exponent and the activation energy were estimated and the creep mechanism was identified.

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.

Effect of W on Deformation Resistance of Co-Bearing 12Cr Ferrite Heat-Resistant Steel for USC Steam Turbines

2010 ◽  
Vol 650 ◽  
pp. 199-204
Author(s):  
Hui Ran Cui ◽  
Feng Sun ◽  
Lan Ting Zhang ◽  
Ai Dang Shan ◽  
Jian Sheng Wu
Keyword(s):  
Activation Energy ◽  
Tensile Tests ◽  
Deformation Resistance ◽  
Diffusion Activation Energy ◽  
Potential Candidate ◽  
Steam Turbines ◽  
Creep Tests ◽  
Self Diffusion ◽  
Heat Resistant ◽  
Arc Melting

12Cr heat resistant steels with different concentration of Co and W, while Mo equivalent (Mo+1/2W) was fixed at 1.6, were prepared by arc-melting and hot rolling. Mechanical properties were evaluated by tensile tests conducted with the strain rate 2×10-5S-1 at 575oC, 600oC and 625oC instead of time-consuming creep tests. The results show that when Co content is fixed, the steel with 1.5 wt% W is found having the best deformation resistance which is strong work hardening and slow strain softening. Apparent activation energy of the steel with 3.1 wt% Co and 1.5 wt% W is in the range of 370~413 kJ/mol, higher than those of the other steels in our study, which are close to the self-diffusion activation energy of iron (239 kJ/mol). Therefore, the steel with 3.1 % Co and 1.5% W is suggested as a potential candidate material for 625oC~650oC class USC steam turbines.

Creep Properties of a High Niobium Containing γ-TiAl Alloy Sheet Material

2002 ◽  
Vol 753 ◽  
Author(s):  
A. Bartels ◽  
S. Bystrzanowski ◽  
R. Gerling ◽  
F.-P. Schimansky ◽  
H. Kestler ◽  
...  
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Elevated Temperatures ◽  
Sheet Material ◽  
Rolling Direction ◽  
Constant Load ◽  
Alloy Sheet ◽  
Tensile Creep ◽  
Creep Tests ◽  
Fine Grained

ABSTRACTIn this study Ti-46Al-9Nb (at%) sheet material processed by a powder metallurgical route was examined. Subsequent to hot rolling the sheets were subjected to a stress-relief treatment at 1273K for 3 hours. During this heat treatment a fine-grained near gamma microstructure has been formed. 100 hours tensile creep tests under constant load were carried out at 700°C in rolling direction, transverse direction as well as 45° direction. Using the method of load changes a stress exponent of 4.1 was determined. Furthermore, the apparent activation energy was determined in the temperature range of 715 – 775°C. Both stress exponent and activation energy suggest that diffusion assisted dislocation climb is the dominant creep mode. A comparison of these results with those of so-called conventional or so-called “2nd generation” γ-TiAl based alloys, e.g. Ti-46.5Al-4(Cr,Nb,Ta,B) (at%) and Ti-47Al-4(Cr,Mn,Nb,Si,B) (at%), indicates a significantly better creep resistance and a higher activation energy of the high Nb containing alloy. Additionally, internal friction experiments were conducted in order to analyze the deformation behavior under very small strains at elevated temperatures.

Creep Behavior of Two Series Magnesium Alloys

2010 ◽  
Vol 638-642 ◽  
pp. 1596-1601 ◽  
Author(s):  
Yang Shan Sun ◽  
Jing Bai ◽  
Feng Xue
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Stress Exponent ◽  
Magnesium Alloys ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Grain Boundary Sliding ◽  
Creep Tests ◽  
Sharp Drop ◽  
Creep Properties

The creep behavior of two series of magnesium alloys, Mg-4Al based alloys with strontium addition and binary Mg-Nd alloys, has been studied. Results show that the high creep properties achieved by the Mg-Nd alloys are attributed to the precipitation of tiny dispersed β’ particles, which form and effectively restrict the dislocation slipping and climb during creep deformation. In terms of values of the stress exponent and apparent activation energy gained from systematic creep tests, the mechanism responsible for creep deformation of the Mg-Nd alloys is inferred as dislocation climb, which is supported by TEM observations performed on the Mg-2Nd alloy after creep test. For the Mg-4Al based alloys, however, microstructural observations reveal that the significant improvement on creep properties caused by Sr addition is accounted for the formation of an interphase network consisting of Al4Sr and a Mg-Al-Sr ternary compound distributing at grain boundaries. The breakage of the interphase network after extrusion results in a sharp drop of creep properties, indicating the creep deformation of the alloy is controlled mainly by grain boundary sliding, which is in contradiction to the mechanism for creep of the alloys inferred by the classical criterions based on the values of stress exponent and apparent activation energy.

In-Situ Measurements of the Activation Energy for D.C. Conduction in Polar ice

1979 ◽  
Vol 22 (87) ◽  
pp. 237-246
Author(s):  
Charles R. Bently
Keyword(s):  
Activation Energy ◽  
Impurity Content ◽  
Apparent Temperature ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Metamorphic History ◽  
True Activation Energy ◽  
Resistivity Variation ◽  
Ionic Impurity

AbstractElectrical resistivity measurements were carried out at station J9 on the Ross Ice Shelf where temperature measurements were available to a depth exceeding three-quarters of the thickness of the shelf. As in a previously published study at a point about 30 km up-steam (Bentley, 1977), the apparent resistivities fit well to a model based upon a steady-state ice shelf with zero bottom balance-rate and an apparent activation energy in the solid ice of 0.15 to 0.25 eV (14–24. kJ mol−1), with preference for the lower end of the range. This model also fits the observed temperature data almost perfectly. Causes of resistivity variation with depth other than the temperature, such as impurity content, metamorphic history, grain size and crystal orientation, probably do not strongly affect the resistivity depth function. Our conclusion is that the true activation energy in the solid ice is less than 0.25 eV (24 kJ mol−1) and perhaps as small as 0.15 eV (14 kJ mol−1), although a reduction by a factor of two or three in the ionic impurity concentration between 50 and 250 m depth cannot be entirely ruled out as a cause of the low apparent temperature effect. A note added in proof indicates that Herron and Langway (in press) have, in fact, reported a decrease in Na+ concentration with increasing depth by a factor of two or three.

scholarly journals Cyclic Creep Behavior and Modified Life Prediction of Bainite 2.25Cr-1Mo Steel at 455 °C

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1486
Author(s):  
Hao Jiang ◽  
Oluwadamilola Ogunmola ◽  
Zizhen Zhao ◽  
Bingbing Li ◽  
Xu Chen
Keyword(s):  
Life Prediction ◽  
Accumulation Rate ◽  
Prediction Method ◽  
Strain Curve ◽  
Cyclic Creep ◽  
Strain Component ◽  
Creep Tests ◽  
Systematic Classification ◽  
Static Creep ◽  
Unloading Rate

Uniaxial static and cyclic creep tests were carried out on bainite 2.25Cr-1Mo steel at 455 °C. Effects of the unloading rate from 0.6 to 39 MPa/s and valley stress duration from 0 to 30 min on the cyclic creep deformation behavior were discussed. The results indicated that the fracture behavior under static and cyclic creep conditions showed a consistent ductile mode. The strain accumulation rate under cyclic creep was significantly retarded as compared with static creep due to the presence of anelastic recovery which was apparently influenced by the unloading conditions. For cyclic creep tests, the unrecoverable strain component determined by a systematic classification of the stress–strain curve was the true damage. A modified life prediction method proposed based on the unrecoverable strain component presented a good life prediction for cyclic creep.

Creep behavior of in situ dual-scale particles-TiB whisker and TiC particulate-reinforced titanium composites

2002 ◽  
Vol 17 (9) ◽  
pp. 2307-2313 ◽  
Author(s):  
Z. Z. Ma ◽  
S. S. Tjong ◽  
X. X. Meng
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Load Transfer ◽  
Lattice Diffusion ◽  
Creep Activation Energy ◽  
Order Of Magnitude ◽  
Scale Particle ◽  
Tic Particulates ◽  
Dual Scale

A titanium composite reinforced by in situ dual-scale particle, high-aspect-ratio TiB whiskers and fine TiC particulates was fabricated by a reactive hot pressing technique from a B4C–Ti system. The composite was subjected to creep investigations in compression at 873–923 K. This composite exhibited a stress exponent of 4.5–4.6 and a creep activation energy of 298 kJ/mol. By comparison, unreinforced Ti exhibited a stress exponent of 5.2–5.3 and a creep activation energy of 259 kJ/mol. No change in the stress exponent with varying creep rates was observed in both composite and unreinforced Ti under the investigated creep rates. The creep resistance of the composite was more than one order of magnitude higher than that of the unreinforced Ti. The load transfer mechanism accounted for this result. The creep of both composite and unreinforced Ti was controlled by lattice diffusion in the titanium matrix.

Sign in / Sign up

Export Citation Format

Share Document