High temperature creep mechanisms in magnesium

Milička, K.; Čadek, J.; Ryš, P.

doi:10.1016/0001-6160(70)90005-2

Cited by 76 publications

(38 citation statements)

References 20 publications

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“…9a); (2) the activation energy is inversely related to the applied stresses (Fig. 11); 11,14) (3) the experimental stress exponent n ¼ 2:2 agrees fairly well with the theoretical n ¼ 2 predicted by the Friedel model. 8,9,11,22) The Friedel mechanism is given schematically in Fig.…”

Section: )supporting

confidence: 65%

“…Milicka et al 14) reported relatively high the stress exponent, n, and the activation energy, Q, and suggested an original explanation of these data. However, other authors 11,13) interpreted the results of Milicka et al 14) to be caused by the presence of fine oxides in the material. At high temperatures, Edelin and Poirier 10) obtained an activation energy essentially higher than the self-diffusion activation energy.…”

Section: Mechanisms Of Plastic Deformationmentioning

confidence: 95%

“…Despite several studies on mechanisms of plastic deformation in pure Mg, 8,10,11,[13][14][15] its deformation behavior is still under discussion. The reason is that, to date, the complete and clear view on the deformation behavior of magnesium is hardly available for wide ranges of temperatures and strain rates, and theoretical models applied to explain the deformation behavior are greatly different.…”

Section: Mechanisms Of Plastic Deformationmentioning

confidence: 99%

“…In earlier studies, 10,14) dislocation climb was assumed as the mechanism controlling deformation. Milicka et al 14) reported relatively high the stress exponent, n, and the activation energy, Q, and suggested an original explanation of these data.…”

Section: Mechanisms Of Plastic Deformationmentioning

confidence: 99%

“…No single interpretation of deformation processes can be suggested to describe the behavior of Mg in the entire temperature range. 8,10,11,[13][14][15] The deformation behavior of Mg was found to be very complicated at temperatures above 523 K. The approach 10,14) explaining this behavior in terms of the transition from hightemperature to low-temperature dislocation climb seems to be inconsistent due to the following reasons:…”

Section: An Examination Of Deformation Mechanisms Inmentioning

confidence: 99%

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Deformation Behavior and Controlling Mechanisms for Plastic Flow of Magnesium and Magnesium Alloy

2003

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Deformation behavior of pure Mg and Mg alloy were studied in the temperature range of 423 to 773 K and at strain rates of 10 À4 -10 À2 s À1 . Three temperature regions can be categorized both in Mg and Mg alloy. The deformation behavior in Mg can be described by an exponantional law at temperatures below 523 K. At the higher temperatures a power law of deformation is valid with the stress exponent close to n ¼ 7 in the intermediate (523-623 K) and 2.2 in the high (673-773 K) temperature ranges. The alloying of Mg with elements such as Zn changes the phenomenology of plastic deformation. An exponantional law is operative at temperatures below 473 K. At above 473 K deformation obeys a power law. The stress exponent is close to n ¼ 7 at intermediate temperatures (473-523 K) and 5 in the high temperature range. An analysis of experimental results shows that alloying changes the controlling mechanisms of plastic deformation and so leads to different deformation behavior in pure Mg and Mg alloy that can be associated with decreasing stacking fault energy (SFE) in Mg alloy. The effect of SFE on the mechanisms of plastic deformation when alloying Mg is discussed.

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Section: )supporting

confidence: 65%

Section: Mechanisms Of Plastic Deformationmentioning

confidence: 95%

Section: Mechanisms Of Plastic Deformationmentioning

confidence: 99%

Section: Mechanisms Of Plastic Deformationmentioning

confidence: 99%

Section: An Examination Of Deformation Mechanisms Inmentioning

confidence: 99%

See 3 more Smart Citations

Deformation Behavior and Controlling Mechanisms for Plastic Flow of Magnesium and Magnesium Alloy

2003

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Stress Relaxation in AX41 Magnesium Alloy Studied at Elevated Temperatures

2007

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For recent years, research and development of magnesium alloys have shown that the Mg-based alloys have great potential for applications as the lightweight materials. Among them, the Mg-Al-Ca alloys exhibit good resistance due to the presence of a heat-stable phase. During plastic deformation in a certain range of temperature and strain rate, different micromechanisms may play important role. The analysis of deformation microstructures has shown that one should consider dislocation-based mechanisms in order to explain the deformation behaviour. It is widely accepted that the resolved shear stress s necessary for the dislocation motion in the slip plane can be divided into two components:where s i is the (internal) athermal contribution to the stress, resulting from long-range internal stresses impeding the plastic flow.where G is the shear modulus, a 1 is a constant describing interaction between dislocations, b is the Burgers vector of dislocations and q t is the total dislocation density. The effective shear stress s* acts on dislocations during their thermally activated motion when they overcome short range obstacles. The mean velocity of dislocations v is connected with the plastic shear strain rate by the Orowan equation:where q m is the density of mobile dislocations. The dislocation velocity (the plastic shear strain rate) is controlled by obstacles (their strength, density) and it depends on temperature and the effective shear stress. In polycrystalline materials, the resolved shear stress s and its components are related to the applied stress r and its corresponding components by the Taylor orientation factor W: r = Ws. A simple relation between the resolved shear strain rate and strain rate is c=We.The most common equation used in describing the average dislocation velocity as a function of the effective stress is an Arrhenius type. The plastic strain rate _ e for a single thermally activated process can be expressed as:where _ e 0 is a pre-exponential factor containing the mobile dislocation density, the average area covered by the dislocations in every activation act, the dislocation Burgers vector, the vibration frequency of the dislocation line, and the geometric factor. T is the absolute temperature and k is the Boltzmann constant. DG(r * ) is the change in the Gibbs free enthalpy depending on the effective stress r * = r ap Àr i and its simple form isHere DG 0 is the Gibbs free enthalpy necessary for overcoming a short range obstacle without the stress and V = bdL is the activation volume where d is the obstacle wide and L is the mean length of dislocation segments between obstacles. It should be mentioned that L may depend on the stress acting on dislocation segments. [**] This work is a part of the research plan MSM 1M2560471601that is financed by the Ministry of Education, Youth and Sports of the Czech Republic. 100ºC ε 0.00 0.02 0.04 0.06 0.08 0.10 σ (MPa) 50 100 150 200 250 σ ap σ R σ i Fig. 1. A part of the true stress-true strain curve at 100°C. The points on the curve indicate the stresses...

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A Review of Different Creep Mechanisms in Mg Alloys Based on Stress Exponent and Activation Energy

et al. 2015

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Magnesium being the lightest structural material, is being increasingly used in automotive industry but at elevated temperatures, alloys like AZ91D, AM60B, AM50A etc. exhibit poor creep resistance which hinders the powertrain applications. This article summarizes the various creep deformation mechanisms prevailing in magnesium alloys at elevated temperatures by the influence of elemental additions. The main creep mechanisms are found to be dislocation climb, diffusion creep, and grain boundary sliding. The variation of creep mechanisms for different Mg alloys with respect to the activation energy (Q), stress exponent (n) for different stresses and temperatures are reported.

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High temperature creep mechanisms in magnesium

Cited by 76 publications

References 20 publications

Deformation Behavior and Controlling Mechanisms for Plastic Flow of Magnesium and Magnesium Alloy

Deformation Behavior and Controlling Mechanisms for Plastic Flow of Magnesium and Magnesium Alloy

Stress Relaxation in AX41 Magnesium Alloy Studied at Elevated Temperatures

A Review of Different Creep Mechanisms in Mg Alloys Based on Stress Exponent and Activation Energy

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