TY  - JOUR
A1  - Fernandez, Ricardo
A1  - Bruno, Giovanni
A1  - Garces, Gerardo
A1  - Nieto-Luis, H.
A1  - Gonzalez-Doncel, Gaspar
T1  - Fractional brownian motion of dislocations during creep deformation of metals
JF  - Materials science & engineering. A, Structural materials
N2  - The present work offers an explanation on how the long-range interaction of dislocations influences their movement, and therefore the strain, during creep of metals. It is proposed that collective motion of dislocations can be described as a fractional Brownian motion. This explains the noisy appearance of the creep strain signal as a function of time. Such signal is split into a deterministic and a stochastic part. These terms can be related to two kinds of dislocation motions: individual and collective, respectively. The description is consistent with the fractal nature of strain-induced dislocation structures predicated in previous works. Moreover, it encompasses the evolution of the strain rate during all stages of creep, including the tertiary one. Creep data from Al99.8% and Al3.85%Mg tested at different temperatures and stresses are used to validate the proposed ideas: it is found that different creep stages present different diffusion characters, and therefore different dislocation motion character.
KW  - Creep
KW  - Aluminum alloys
KW  - Dislocation motion
KW  - Diffusion
KW  - Fractal
KW  - structures
Y1  - 2020
U6  - https://doi.org/10.1016/j.msea.2020.140013
SN  - 0921-5093
SN  - 1873-4936
VL  - 796
PB  - Elsevier
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Fernandez, Ricardo
A1  - Gonzalez-Doncel, Gaspar
A1  - Garces, Gerardo
A1  - Bruno, Giovanni
T1  - Towards a comprehensive understanding of creep
BT  - microstructural dependence of the pre-exponential term in Al
JF  - Materials science & engineering. A, Structural materials: properties, microstructure and processing
N2  - We show that the equation proposed by Takeuchi and Argon to explain the creep behavior of Al-Mg solid solution can be used to describe also the creep behavior of pure aluminum. In this frame, it is possible to avoid the use of the classic pre-exponential fitting parameter in the power law equation to predict the minimum creep strain rate. The effect of the fractal arrangement of dislocations, developed at the mesoscale, must be considered to fully explain the experimental data. These ideas allow improving the recently introduced SSTC model, fully describing the primary and secondary creep regimes of aluminum alloys without the need for fitting. Creep data from commercially pure A199.8% and Al-Mg alloys tested at different temperatures and stresses are used to validate the proposed ideas.
KW  - creep
KW  - Aluminum alloys
KW  - dislocations
KW  - fractal
KW  - stress exponent
Y1  - 2020
U6  - https://doi.org/10.1016/j.msea.2020.139036
SN  - 0921-5093
SN  - 1873-4936
VL  - 776
PB  - Elsevier
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Cabeza, Sandra
A1  - Müller, Bernd R.
A1  - Pereyra, Ricio
A1  - Fernandez, Ricardo
A1  - Gonzalez-Doncel, Gaspar
A1  - Bruno, Giovanni
T1  - Evidence of damage evolution during creep of Al-Mg alloy using synchrotron X-ray refraction
JF  - Journal of applied crystallography
N2  - In order to provide further evidence of damage mechanisms predicted by the recent solid-state transformation creep (SSTC) model, direct observation of damage accumulation during creep of Al-3.85Mg was made using synchrotron X-ray refraction. X-ray refraction techniques detect the internal specific surface (i.e. surface per unit volume) on a length scale comparable to the specimen size, but with microscopic sensitivity. A significant rise in the internal specific surface with increasing creep time was observed, providing evidence for the creation of a fine grain substructure, as predicted by the SSTC model. This substructure was also observed by scanning electron microscopy.
KW  - aluminium alloys
KW  - creep
KW  - damage
KW  - synchrotron X-ray refraction
KW  - electron microscopy
KW  - subgrain structure
Y1  - 2018
U6  - https://doi.org/10.1107/S1600576718001449
SN  - 1600-5767
VL  - 51
SP  - 420
EP  - 427
PB  - International Union of Crystallography
CY  - Chester
ER  -