Thermally Activated Dislocation Motion in an AS21 Alloy and Alloy Reinforced with Short Ceramic Fibres Studied at Elevated Temperatures

2013 ◽  
Vol 592-593 ◽  
pp. 71-74
Author(s):  
Zuzana Zdražilová ◽  
Zuzanka Trojanová ◽  
Kristián Máthis ◽  
Pavel Lukáč
Keyword(s):  
Magnesium Alloy ◽  
Stress Relaxation ◽  
Applied Stress ◽  
Elevated Temperatures ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Dislocation Motion ◽  
Thermally Activated ◽  
Effective Components ◽  
Thermally Activated Process

AS21 magnesium alloy (2.1Al-1Si-balance Mg in wt.%) and the alloy reinforced with short δ-Al2O3fibres (Saffil®) were deformed in compression at temperatures between 23 and 300 °C. Stress relaxation tests were performed in order to reveal features of the thermally activated dislocation motion. Internal and effective components of the applied stress have been estimated. The activation volume decreases with increasing effective stress. The values of the activation volume and the activation enthalpy indicate that the main thermally activated process in the alloy as well as in the composite is the dislocation motion in non-compact planes.

Stress Relaxation in an AZ31 Magnesium Alloy

2011 ◽  
Vol 465 ◽  
pp. 101-104 ◽  
Author(s):  
Pavel Lukáč ◽  
Zuzanka Trojanová
Keyword(s):  
Magnesium Alloy ◽  
Stress Relaxation ◽  
Deformation Temperature ◽  
Room Temperature ◽  
Activation Volume ◽  
Initial Strain Rate ◽  
Az31 Magnesium Alloy ◽  
Thermally Activated ◽  
Relaxation Curves ◽  
Thermally Activated Process

Stress relaxation tests have been used in order to determine parameters of a possible thermally activated process in AZ31 magnesium alloy. The samples were deformed at a constant initial strain rate of 6.7x10-5 s-1 at various temperatures between room temperature and 300 °C. Stress relaxation, i.e. a decrease in the stress with time, was measured at various stress levels and at various temperatures. An analysis of the stress relaxation curves enabled to estimate the internal stress as a function of the strain and the test temperature. It has been shown that the activation volume is a function of the effective stress independently of the deformation temperature.

Mechanical Properties of γ-TiAl Based Alloys at Elevated Temperatures

2000 ◽  
Vol 646 ◽  
Author(s):  
M. Weller ◽  
A. Chatterjee ◽  
G. Haneczok ◽  
F. Appel ◽  
H. Clemens
Keyword(s):  
High Temperature ◽  
Elevated Temperatures ◽  
Activation Enthalpy ◽  
Low Frequency ◽  
Loss Peak ◽  
Mechanical Loss ◽  
Creep Tests ◽  
Thermally Activated ◽  
Diffusion Controlled ◽  
Mechanical Spectra

ABSTRACTMechanical loss (internal friction) and creep experiments were carried out on specimens of a Ti-46.5at.%Al-4at.%(Cr,Nb,Ta,B) alloy with differently spaced fully lamellar microstructures. The creep tests were performed in a temperature range of 970 K to 1070 K at 175 MPa. For the mechanical loss measurements a low frequency subresonance torsion apparatus was applied, operating in the frequency range of 0.01 Hz to 10 Hz. The mechanical spectra show two phenomena: (i) A loss peak of Debye-type at 900 K (0.01 Hz) which is controlled by an activation enthalpy of 3.0 eV. The loss peak is related to thermally activated (reversible) motion of dislocation segments which are pinned at the lamellae interface and within gamma lamellae. (ii) A viscoelastic high temperature background above 1000 K with an activation enthalpy of 3.8 eV. This value agrees well with the activation enthalpy of 3.6 eV from creep experiments. Both high temperature background as well as creep are assigned to diffusion controlled climb of dislocations.

Deformation Behavior And Internal Stress Of Icosahedral Al-Pd-Mn With Decagonal Phase Lamellae At Elevated Temperatures

1998 ◽  
Vol 553 ◽  
Author(s):  
H. Hirai ◽  
T. Tomita ◽  
F. Yoshida ◽  
H. Nakashima
Keyword(s):  
Stress Relaxation ◽  
Strain Rate ◽  
Internal Stress ◽  
Stress Exponent ◽  
Deformation Behavior ◽  
Elevated Temperatures ◽  
Initial Strain Rate ◽  
Decagonal Phase ◽  
Thermally Activated ◽  
High Internal Stress

AbstractFine decagonal phase lamellae-bearing icosahedral Al-Pd-Mn quasicrystals were tested compressionally at temperatures of 997 to 1073 K and initial strain rate of 3 × 10−5. to I × 10−4 S−1, and stress relaxation tests were performed at various stages of deformation. The results confirmed the thermally activated nature of deformation, and the stress exponent of strain rate was around 4. Internal stress for deformation estimated by Kikuchi's method reached 50 to 90 % of applied stress. The effective stress exponent of strain rate was revealed to be about 1.3. At least a part of high internal stress was attributable to complicated dislocation microstructure.

Internal stress and thermally activated dislocation motion in an AZ63 magnesium alloy

2011 ◽  
Vol 130 (3) ◽  
pp. 1146-1150 ◽  
Author(s):  
Zuzanka Trojanová ◽  
Kristián Máthis ◽  
Pavel Lukáč ◽  
Gergely Németh ◽  
František Chmelík
Keyword(s):  
Magnesium Alloy ◽  
Internal Stress ◽  
Dislocation Motion ◽  
Thermally Activated

Correlation of Stress Relaxation and Microstructure Change in Polycrystalline Thin Films on Substrates: Au on Si at RT

1991 ◽  
Vol 230 ◽  
Author(s):  
A. C. Vermeulen ◽  
R. Delhez ◽  
E. J. Mittemeijer
Keyword(s):  
Stress Relaxation ◽  
Dislocation Density ◽  
Room Temperature ◽  
Dominant Role ◽  
Dislocation Motion ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thermally Activated ◽  
Polycrystalline Thin Films ◽  
Simultaneous Decrease

AbstractStress relaxation in polycrystalline layers can be explained by processes, in which the microstructure plays a dominant role. The microstructure itself may also be subjected to changes. With X-ray diffraction information about both the stress and the microstructure can be obtained without destroying the specimen and without disturbing the stress relaxation process.In this paper a model system is studied: Au on Si<100>. The specimens showed a simultaneous decrease of macrostress and dislocation density with time at room temperature. This could be interpreted on the basis of a model founded on thermally activated dislocation motion. It followed that the grain size is an important parameter for the change of the dislocation density.

Low-temperature deformation of body-centred cubic metals. II. Mechanism of thermally activated flow

1964 ◽  
Vol 281 (1385) ◽  
pp. 240-257 ◽  
Keyword(s):  
Low Temperature ◽  
Low Temperatures ◽  
Activation Volume ◽  
Temperature Deformation ◽  
Cubic Metals ◽  
Thermally Activated ◽  
Free Energy Of Activation ◽  
Peierls Barrier ◽  
Straight Dislocation ◽  
Thermally Activated Process

The experimental results of I indicate that the dislocation velocity is limited by a thermally activated process, and the parameters of the appropriate rate equation are evaluated. At very low temperatures, the stress derivative of the free energy of activation (the 'activation volume’) is only a few atomic volumes. It is very difficult to explain the magnitude of the low-temperature stress or that of the activation volume if direct dislocation—impurity interactions are responsible for most of the resistance to motion, and it is concluded that there is probably a significant lattice interaction (a ‘Peierls-Nabarro force’). The results are compared with the predictions of recent models for the overcoming of the Peierls barrier by the production of double kinks in straight dislocation lines.

Simulation of Dislocation Dynamics in Ni3Al: A Study of Velocity Autocorrelations

1999 ◽  
Vol 578 ◽  
Author(s):  
C. K. Erdonmez ◽  
D. C. Chrzan
Keyword(s):  
Yield Strength ◽  
Applied Stress ◽  
Critical Stress ◽  
Threshold Stress ◽  
Dislocation Motion ◽  
Cross Slip ◽  
Dislocation Dynamics ◽  
Thermally Activated ◽  
Simple Rules ◽  
Isotropic Elasticity

AbstractThe yield strength anomaly in some L12 compounds has been linked to the thermally assisted cross slip of screw superdislocations. This work continues earlier efforts to understand the yield strength anomaly in L12 alloys using computer simulations of dislocation motion. Dislocations are modelled within isotropic elasticity theory, and simple rules are used to model the cross-slip process in the two dimensional geometry of the simulation. The velocity of a single dislocation in Ni3Al is studied as a function of the applied stress. The observed velocities vary nonlinearly with the applied stress. Further, dislocations are observed to become immobile for small applied loads. At high stresses, the dislocations are observed to advance relatively unhindered by the thermally activated cross slip process. Fluctuations in the velocity of the dislocations are studied, and their autocorrelation function shows an increased correlation time near a threshold stress. This threshold stress is identified with the critical stress proposed in earlier works.

scholarly journals Stress Relaxation in AX41 Magnesium Alloy Studied at Elevated Temperatures

2007 ◽  
Vol 9 (5) ◽  
pp. 370-374 ◽  
Author(s):  
Z. Trojanová ◽  
P. Lukác ◽  
K. U. Kainer
Keyword(s):  
Magnesium Alloy ◽  
Stress Relaxation ◽  
Elevated Temperatures
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