Correlation of Creep Properties by a Diffusion Analogy

1952 ◽  
Vol 19 (3) ◽  
pp. 320-326
Author(s):  
Leon Green
Keyword(s):  
Activation Energy ◽  
Time Behavior ◽  
Creep Equation ◽  
Creep Properties ◽  
Self Diffusion ◽  
Polycrystalline Metals ◽  
Similar Temperature Dependence ◽  
Similar Temperature ◽  
Apparent Activation Energies ◽  
Undetermined Constant

Abstract The necessity of atom movements for both creep and self-diffusion suggests a method of correlating the constant-stress creep properties of pure metals. The concept of steady-state creep is discarded, and two empirical approximations for the strain-time behavior of pure polycrystalline metals lead to a creep equation defining an activation energy as the only undetermined constant. For cases where the orientation of individual crystals is important, a second constant is required. Application of this equation to published creep data effects a correlation which indicates that the apparent activation energies observed for creep and self-diffusion show a similar temperature dependence. The effect of stress upon the activation energy for several metals is described approximately, but the need for further experiments encompassing lower values of stress is revealed. The qualitative effects of impurities, grain size, cold-working, and surface conditions upon creep as predicted by a diffusion analogy are found to be in agreement with experimental results, but it is noted that the analogy does not hold if creep deformation is obtained as a result of slip.

scholarly journals Effect of CaO on catalytic combustion of semi-coke

2021 ◽  
Vol 10 (1) ◽  
pp. 011-020
Author(s):  
Luyao Kou ◽  
Junjing Tang ◽  
Tu Hu ◽  
Baocheng Zhou ◽  
Li Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Combustion Rate ◽  
Activation Energies ◽  
Combustion Reaction ◽  
Tg Analysis ◽  
Conversion Rates ◽  
Apparent Activation Energies ◽  
Ozawa Integral Method ◽  
Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

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.

Doping Effect in Nickel Oxide

2009 ◽  
Vol 289-292 ◽  
pp. 775-782 ◽  
Author(s):  
Zbigniew Jurasz ◽  
Krzysztof Adamaszek ◽  
Romuald Janik ◽  
Zbigniew Grzesik ◽  
Stanisław Mrowec
Keyword(s):  
Activation Energy ◽  
Nickel Oxide ◽  
High Temperatures ◽  
Oxygen Pressure ◽  
Pressure Dependence ◽  
Oxidation Rate ◽  
Doping Effect ◽  
Self Diffusion ◽  
Electron Holes ◽  
Influence Of Impurities

Detailed investigations of nonstoichiometry as well as chemical and self-diffusion in nickel oxide have shown that doubly ionised cation vacancies and electron holes are the predominant defects in this material. The present work is an attempt to demonstrate that aliovalent impurities (Cr, Al, Na and Li) may considerably influence the concentration of these defects and, consequently, the oxidation rate of nickel at high temperatures. It has been shown that small amounts of tri-valent impurities (Cr, Al) bring about an increase of the oxidation rate, while mono-valent ones (Li, Na) decrease the rate of oxidation. These phenomena may satisfactorily be explained in terms of a doping effect. All experiments have been carried out as a function of temperature (1373-1673 K) and oxygen pressure (1-105 Pa) and consequently, it was possible to determine the influence of impurities not only on the oxidation rate but also on the activation energy of reaction and its pressure dependence. The results of these investigations could again be elucidated in terms of doping effect.

Electrical Properties of β-FeSi2 Thin Films on Insulating Substrates

2003 ◽  
Vol 796 ◽  
Author(s):  
Kensuke Akiyama ◽  
Takeshi Kimura ◽  
Shin Nishiyama ◽  
Takeo Hattori ◽  
Naoki Ohashi ◽  
...  
Keyword(s):  
Thin Films ◽  
Iron Silicide ◽  
Amorphous Film ◽  
Rf Magnetron Sputtering ◽  
Atomic Ratio ◽  
Similar Temperature Dependence ◽  
Electrical Conductivities ◽  
Similar Temperature ◽  
Band Conduction ◽  
Insulating Substrates

ABSTRACTIron silicide thin films were prepared on insulating substrates using RF magnetron sputtering method. Amorphous, polycrystalline and epitaxial β-FeSi2 were obtained on MgO(001), Al2O3(110) and Al2O3(001) substrates, respectively. Electrical conductivities of these films showed similar temperature dependence. Intrinsic band conduction and hopping conduction mechanism were predominant above and below 600K, respectively. The localized ordering in the polycrystalline and epitaxial films that controled the movement of carriers were as low as in the amorphous film. For the epitaxial β-FeSi2 film, electrical conductivity below 600K were affected by atomic ratio of silicon to iron (Si/Fe) in the films, because the localized ordering in the films decreased as Si/Fe atomic ratio decreased.

scholarly journals Probing the Locally Generated Even and Odd Order Nonlinearity in Y–Ba–Cu–O and Tl–Ba–Ca–Cu–O (2212) Microwave Resonators Around <img src="/images/tex/19586.gif" alt="T_{\rm C}">

2013 ◽  
Vol 23 (3) ◽  
pp. 9000105-9000105 ◽  
Author(s):  
Brooke Jeries ◽  
Sean Cratty ◽  
S Remillard
Keyword(s):  
Meissner Effect ◽  
Second Order ◽  
Intermodulation Distortion ◽  
Coaxial Cable ◽  
Superconducting Resonators ◽  
Third Order ◽  
Odd Order ◽  
Similar Temperature Dependence ◽  
Similar Temperature ◽  
Lower Temperature

Spatial scanning of the synchronously generated second- and third-order intermodulation distortion in superconducting resonators uncovers local nonlinearity hot spots, and possible time reversal symmetry breaking, using a simple probe fashioned from coaxial cable. It is clear that even and odd order nonlinearity in these samples do not share the same physical origins, because their temperature and static magnetic field dependences are quite different. 2nd order intermodulation distortion remains strong in these measurements as the temperature continues to drop belowTCto 77 K even though the 3rd order peaks nearTCand becomes smaller at lower temperature as predicted by the nonlinear Meissner effect. Both YBa2Cu3O7and Tl2Ba2CaCu2O8resonators of the same structure exhibit similar temperature dependence in the second order with second order remaining high at lower temperature. The YBa2Cu3O7sample has lower third-order intermodulation distortion with a pronounced peak atTC.

High Temperature Creep Behavior and Effects of Stacking Fault Energy in Mg-Y and Mg-Y-Zn Dilute Solid Solution Alloys

2014 ◽  
Vol 783-786 ◽  
pp. 491-496
Author(s):  
Mayumi Suzuki ◽  
Yasuyuki Murata ◽  
Kyosuke Yoshimi
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
Creep Behavior ◽  
Ternary Alloys ◽  
Dislocation Creep ◽  
Prismatic Slip ◽  
Dislocation Slip ◽  
Self Diffusion ◽  
Controlling Mechanism ◽  
Hot Rolled

Compressive creep behavior of hot-rolled (40%) Mg-Y binary and Mg-Y-Zn ternary dilute solid solution alloys are investigated in this study. Creep strength is substantially improved by the addition of zinc. Activation Energy for creep in Mg-Y and Mg-Y-Zn alloys are around 200 kJ/mol at the temperature range from 480 to 570 K. These values are higher than the activation energy for self-diffusion coefficient in magnesium (135 kJ/mol). Many stacking faults, which are planar type defects are observed on the basal planes of the magnesium matrix in Mg-Y-Zn ternary alloys. TEM observation has been revealed that the non-basal a-dislocation slip is significantly activated by these alloys. The rate controlling mechanism of Mg-Y and Mg-Y-Zn dilute alloys are considered to the cross-slip or prismatic-slip controlled dislocation creep with high activation energy for creep, more than 1.5 times higher than the activation energy for creep controlled dislocation climb.

scholarly journals New Developments in Understanding Harper-Dorn, Five- power Law Creep and Power-law Breakdown

2020 ◽  
Author(s):  
michael kassner
Keyword(s):  
Stress Exponent ◽  
Power Law ◽  
Dislocation Network ◽  
Creep Equation ◽  
Self Diffusion ◽  
Wide Range ◽  
Recent Developments ◽  
Initial Dislocation Density ◽  
Power Law Creep ◽  
Edge Dislocations

This paper discusses recent developments in creep, over a wide range of temperature, that mqy change our understanding of creep. The five-power law creep exponent (3.5 to 7) has never been explained in fundamental terms. The best the scientific community has done is to develop a natural three power-law creep equation that falls short of rationalizing the higher stress exponents that are typically five. This inability has persisted for many decades. Computational work examining the stress-dependence of the climb rate of edge dislocations we may rationalize the phenomenological creep equations. Harper-Dorn creep, “discovered” over 60 years ago has been immersed in controversy. Some investigators have insisted that a stress exponent of one is reasonable. Others believe that the observation of a stress exponent of one is a consequence of dislocation network frustration. Others believe the stress exponent is artificial due to the inclusion of restoration mechanisms such as dynamic recrystallization or grain growth that is not of any consequence in the five power-law regime. Also, the experiments in the Harper-Dorn regime, which accumulate strain very slowly (sometimes over a year) may not have attained a true steady state. New theories suggest that absence or presence of Harper-Dorn may be a consequence of the initial dislocation density. Novel experimental work suggests that power-law breakdown may be a consequence of a supersaturation of vacancies which increase self-diffusion.

TEMPERATURE COEFFICIENTS FOR SELF-DIFFUSION IN SOLUTION

1954 ◽  
Vol 32 (2) ◽  
pp. 71-78 ◽  
Author(s):  
C. J. Krauss ◽  
J. W. T. Spinks
Keyword(s):  
Activation Energy ◽  
Aqueous Solutions ◽  
Infinite Dilution ◽  
Kcal Mole ◽  
Self Diffusion ◽  
Temperature Coefficients ◽  
Sodium Dihydrogen

Coefficients of self-diffusion have been measured for aqueous solutions of sodium dihydrogen phosphates from 1 molar to 10−4 molar and at temperatures of 15, 25, 35, and 45 °C. The activation energy of self-diffusion has been calculated for various concentrations. It decreases from 5.4 kcal./mole at 0.9 M to 4.3 kcal./mole. at infinite dilution.

Nonlinear Damage Creep Model of Coal or Rock Containing Gas

2012 ◽  
Vol 204-208 ◽  
pp. 289-296
Author(s):  
Xiao Bin Yang ◽  
Yang Li ◽  
Hai He Guan ◽  
Tian Yang Li ◽  
Jie Shan He
Keyword(s):  
Gas Absorption ◽  
Creep Model ◽  
Creep Experiment ◽  
Creep Equation ◽  
Stick Slip ◽  
Kelvin Model ◽  
Creep Properties ◽  
Material Parameters ◽  
Whole Process ◽  
Creep Curves

In order to study the creep properties of coal or rock containing gas, the creep properties of coal or rock without gas were studied firstly. Through analyzing the previous creep experiment results of coal or rock, one nonlinear damage creep model of coal or rock was founded based on the general Kelvin model. In this model, assumed that the damage is a function of stress level and time, and introduced one nonlinear hardened function into the general Kelvin model, the nonlinear damage fading creep equation and the nonlinear damage creep whole process equation were obtained. Besides this model, considering the composite structure of coal or rock, gas and gas absorption layer, and assuming that this structure has the stick-slip property under the outside load, so a stick-slip module was added in the general Kelvin model and a new nonlinear damage creep model of coal or rock containing gas was founded. Given the value of the material parameters in the two equations, the creep curves varied with the time were drawn under different axial compression. Through the theoretical curves, the nonlinear damage creep model in this paper was proved to be rational.

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