Florian Torre - Academia.edu (original) (raw)
Papers by Florian Torre
Acta Mater, 2002
The microstructure of commercially available nanocrystalline (nc) electroplated Ni foils is studi... more The microstructure of commercially available nanocrystalline (nc) electroplated Ni foils is studied by means of X-ray diffraction and transmission electron microscopy. It is shown that the microstructure is inhomogeneous and batch-dependent. Tensile properties at strain rates between 10−5 and 103 s−1 are studied and compared with the results of coarse-grained Ni. Data on strength, strain-rate sensitivity and work hardening are presented. At the highest strain rates, shear banding with local grain growth is observed in the nc structure. It is also suggested that the differences found in nc Ni for 3 and 20 mm tensile specimens are the size effects related to the inhomogeneous microstructure.
Acta Materialia, Feb 1, 2008
Two eutectic multicomponent La-based alloys with high glass-forming ability were identified by ul... more Two eutectic multicomponent La-based alloys with high glass-forming ability were identified by ultrahigh acceleration centrifugal processing during cooling of compositionally off-eutectic melts. The identified ternary composition, La 64 Al 13 Cu 23 , was cast amorphously to 3 mm in diameter, comparable to previous studies. The quaternary composition, La 65 Al 13 Ni 10 Cu 12 , was cast to 10 mm in diameter, showing the highest glass-forming ability for this system. These results show that instead of extensive traditional alloy development, it is sufficient to study one centrifugally processed sample to discover the composition with the deepest eutectic, which (as predicted by Turnbull) produces good glass-forming ability.
Journal of the Mechanical Behavior of Biomedical Materials, 2016
Mater Sci Eng a Struct Mater, 2006
Microstructure evolution, workability, and post-working fatigue behavior were established for alu... more Microstructure evolution, workability, and post-working fatigue behavior were established for aluminum alloy 2124-T851 processed via equal channel angular extrusion (ECAE) with back pressure. ECAE without back pressure resulted in complete fracture during the first pass. On the other hand, ECAE with back pressure enabled the production of sound material with significant grain refinement to the nano-scale. In contrast to typical property trends, an attractive combination of tensile ductility and LCF fatigue life was obtained as well as improved strength and HCF fatigue life compared to coarse-grained material in the as-received (T851) condition.
Phil Mag Lett, 2007
ABSTRACT Micromechanical analysis of ductile bulk metallic glasses at various temperatures and st... more ABSTRACT Micromechanical analysis of ductile bulk metallic glasses at various temperatures and strain rates revealed accurate information on inhomogeneous flow kinetics. The disappearance of flow instabilities (i.e. serrations) at low temperatures correlates with a change from negative to positive strain-rate sensitivity and exhibits an activation energy of 0.37 eV. Based on these findings, a constitutive deformation model for thermally-activated flow in disordered systems is presented, which accounts for possible structural relaxation processes within the shear bands. Similarities in the flow behaviour of bulk metallic glasses with the Portevin-Le Châtelier effect known for crystalline metals are discussed.
Scripta Mater, 2005
ABSTRACT Tensile properties and microstructure of Danocrystalline electrodeposited Ni at temperat... more ABSTRACT Tensile properties and microstructure of Danocrystalline electrodeposited Ni at temperatures between room temperature and 330° C are presented. Above 300° C low flow stress and high tensile elongation are observed along with grain growth and segregation of sulphur to the grain boundaries causing the formation of a Ni-sulphide phase. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
International Journal of Earth Sciences, 2010
The Valais units in Savoy (Zone des Brèches de
Materials Processing Handbook, 2007
Physical Review Letters, 2011
In situ acoustic emission monitoring is shown to capture the initiation of shear bands in metalli... more In situ acoustic emission monitoring is shown to capture the initiation of shear bands in metallic glasses. A model picture is inferred from stick-slip flow in granular media such that the origin of acoustic emission is attributed to a mechanism of structural dilatation. By employing a quantitative approach, the critical volume change associated with shear-band initiation in a metallic glass is estimated to be a few percent only. This result agrees with typical values of excess free volume found in the supercooled liquid regime near the glass transition temperature.
Nanoscale, 2009
We present a method where epsilon-cobalt nanoparticles with an average diameter of 4.5 nm can be ... more We present a method where epsilon-cobalt nanoparticles with an average diameter of 4.5 nm can be synthesized in a controlled process and in significantly larger quantities than previously reported in the literature, based on the thermal decomposition of dicobaltoctacarbonyl in the presence of oleic acid and trioctylphosphine oxide (TOPO). Moreover, since the resulting particles are coated with an oleate layer, as shown by infrared (IR) spectroscopy, the colloids can be re-dispersed in organic solvents. These dispersions are suitable for the preparation of nanocomposites by a simple procedure, i.e. mixing of the cobalt dispersion with a polymer solution followed by casting and solvent evaporation. Magnetization measurements confirm the expected superparamagnetic behavior for both the cobalt nanoparticles and the metal-polymer nanocomposites.
Metallurgical and Materials Transactions A, 2007
The microstructure and texture of copper subjected to equal channel angular extrusion (ECAE) via ... more The microstructure and texture of copper subjected to equal channel angular extrusion (ECAE) via route B C for up to 16 passes have been assessed using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), X-ray diffraction (XRD) peak broadening, and texture analysis. The differences in grain size measured by these techniques allows for an understanding of microstructural evolution. A gradual decrease in grain size occurs with an increasing number of passes, while the subgrain size remains approximately constant. Up to four passes, the fraction of high-angle grain boundaries (HAGBs) (>15 deg) increases from 15 to 45 pct, but remains constant thereafter. The grain boundary character distribution shows a decrease of S1 boundaries and an increase of S3 boundaries with higher passes. After 16 passes, a few regions of large 1 to 4 lm sized grains embedded in a submicrometer sized matrix were observed. These agglomerates of larger grain diameters together with the measured decrease in the dislocation density correlate with the observed decrease in yield strength of samples subjected to four and more passes. Texture evolution is adequately described under conditions of negative simple shear. The effect of increased accumulated strain results in an overall spread of orientation densities due to the absence of stable end positions post-ECAE. Detailed microstructural information suggests that strengthening mechanisms in the material can be sufficiently well described by the classical Hall-Petch relationship by applying it to the subgrain size, while the subgrain size remains smaller than the grain size.
MATERIALS TRANSACTIONS, 2007
New findings on the inhomogeneous plastic deformation of bulk metallic glasses (BMGs) have shown ... more New findings on the inhomogeneous plastic deformation of bulk metallic glasses (BMGs) have shown a disappearance of serrated flow below a critical temperature or above a critical strain rate. This correlates with a change in the strain rate sensitivity (SRS) from negative to positive values, suggesting a change in the deformation mechanism. In addition, a change in the SRS correlating with the increase in the stress drop magnitude is observed with increasing strain. Results on the serration and flow dependence for the binary BMG Cu 50 Zr 50 show close phenomenological similarities with the Portevin -Le Châtelier or dynamic strain aging effect known for crystalline solids. An alternative model for the appearance and disappearance of serrated flow based on the structural relaxation of the atomic configuration of shear transformation zones is described. [
Materials Science and Engineering: A, 2006
Progressive texture evolution during the second pass of equal channel angular extrusion (ECAE) of... more Progressive texture evolution during the second pass of equal channel angular extrusion (ECAE) of copper via route B C was investigated by interrupting the extrusion and measuring the textures of seven sections starting within the entry channel, continuing through the die corner region, and ending within the exit channel. Experimental textures showed the development of {1 1 1} u v w θ and {h k l} 1 1 0 θ partial fibers; and that the most significant texture changes occurred near the die intersection plane. Consistent texture predictions were achieved by visco-plastic selfconsistent modelling (VPSC) using finite element (FE)-predicted deformation history. The FE simulation from the center of the billet cross-section indicated that the deviation of ECAE deformation from simple shear at the intersection of the die channels was not significant.
Materials Science and Engineering: A, 2006
Texture and microstructural evolution of interstitial-free (IF) steel and copper (Cu) subjected t... more Texture and microstructural evolution of interstitial-free (IF) steel and copper (Cu) subjected to room temperature equal channel angular extrusion for N = 1, 2 and 4 passes, route B C were compared. Both materials exhibit texture development similar to simple shear. Orientations of E {0 1 1} 1 1 1 and D {1 1 2} 1 1 1 type components are most prominent for IF-steel, while maximum intensities for A andĀ {1 1 1} 1 1 0 components were found in Cu. Quantitative texture and difference indices indicate a general increase up to the second pass followed by a decrease at the end of four passes. Following each pass, the five most dominant orientations were used to quantify the change in Taylor factor estimate for simulated uniaxial tensile deformation along the three principal deformation directions. The results show approximately equivalent estimates for both materials after four passes and reflect increasing microstructural homogeneity after a full 360 • revolution of the billet longitudinal axis. Transmission electron microscopy shows strongly aligned lamellar boundaries oriented along the major slip planes and directions of bcc and fcc structures. After four passes, the refined microstructure is characterised by an average subgrain size of ∼230 for IF-steel and ∼170 nm for Cu.
Journal of Materials Science, 2007
Journal of Materials Chemistry, 2012
... André R. Studart*a, Adrienne Nelsonb, Boris Iwanovskyb, Martin Kotyrbab, Andreas A. Kündigb, ... more ... André R. Studart*a, Adrienne Nelsonb, Boris Iwanovskyb, Martin Kotyrbab, Andreas A. Kündigb, Florian H. Dalla Torreb, Urs T. Gonzenbachc, Ludwig J. Gaucklerc and Jörg F. Löfflerb. ... 13, HJ Jin and J. Weissmuller, Adv. Eng. ...
Journal of Alloys and Compounds, 2010
At low homologous temperatures metallic glasses exhibit inhomogeneous flow behaviour, which is as... more At low homologous temperatures metallic glasses exhibit inhomogeneous flow behaviour, which is associated with narrow shear banding. Based on the width of the shear bands and the time-dependent heat conduction, we show here that this process is not fully adiabatic at low strain rates, even though temperatures are sufficiently high to create a drop in viscosity within either a new or a pre-existing shear band. Evaluation of the deformation kinetics at cryogenic temperatures suggests an increase in viscosity within the shear band, although temperatures are still sufficiently high to cause localised melting at fracture. In addition, a change from serrated to non-serrated flow can be observed if the temperature is lowered below a critical value. This macroscopic change in the flow behaviour is directly related to a change in the strain rate sensitivity from negative to positive values, suggesting a clear change in deformation behaviour. We propose a refined shear dilatation model to explain the experimental findings.
Applied Physics Letters, 2006
ABSTRACT Detailed investigations were carried out on the deformation behavior of Zr-based monolit... more ABSTRACT Detailed investigations were carried out on the deformation behavior of Zr-based monolithic bulk metallic glass and bulk metallic glass matrix composites. The latter, due to splitting and multiplication of shear bands, exhibits larger compressive strains than the former, without significant loss of strength. Serrated flow in conjunction with a negative strain rate sensitivity was observed in both materials. This observation, together with an increase in stress drops with increasing strain and their decrease with increasing strain rate, indicates phenomenologically close similarities with the dynamic strain aging deformation mechanism known for crystalline solids. The micromechanical mechanism of a shear event is discussed in light of these results.
Acta Mater, 2002
The microstructure of commercially available nanocrystalline (nc) electroplated Ni foils is studi... more The microstructure of commercially available nanocrystalline (nc) electroplated Ni foils is studied by means of X-ray diffraction and transmission electron microscopy. It is shown that the microstructure is inhomogeneous and batch-dependent. Tensile properties at strain rates between 10−5 and 103 s−1 are studied and compared with the results of coarse-grained Ni. Data on strength, strain-rate sensitivity and work hardening are presented. At the highest strain rates, shear banding with local grain growth is observed in the nc structure. It is also suggested that the differences found in nc Ni for 3 and 20 mm tensile specimens are the size effects related to the inhomogeneous microstructure.
Acta Materialia, Feb 1, 2008
Two eutectic multicomponent La-based alloys with high glass-forming ability were identified by ul... more Two eutectic multicomponent La-based alloys with high glass-forming ability were identified by ultrahigh acceleration centrifugal processing during cooling of compositionally off-eutectic melts. The identified ternary composition, La 64 Al 13 Cu 23 , was cast amorphously to 3 mm in diameter, comparable to previous studies. The quaternary composition, La 65 Al 13 Ni 10 Cu 12 , was cast to 10 mm in diameter, showing the highest glass-forming ability for this system. These results show that instead of extensive traditional alloy development, it is sufficient to study one centrifugally processed sample to discover the composition with the deepest eutectic, which (as predicted by Turnbull) produces good glass-forming ability.
Journal of the Mechanical Behavior of Biomedical Materials, 2016
Mater Sci Eng a Struct Mater, 2006
Microstructure evolution, workability, and post-working fatigue behavior were established for alu... more Microstructure evolution, workability, and post-working fatigue behavior were established for aluminum alloy 2124-T851 processed via equal channel angular extrusion (ECAE) with back pressure. ECAE without back pressure resulted in complete fracture during the first pass. On the other hand, ECAE with back pressure enabled the production of sound material with significant grain refinement to the nano-scale. In contrast to typical property trends, an attractive combination of tensile ductility and LCF fatigue life was obtained as well as improved strength and HCF fatigue life compared to coarse-grained material in the as-received (T851) condition.
Phil Mag Lett, 2007
ABSTRACT Micromechanical analysis of ductile bulk metallic glasses at various temperatures and st... more ABSTRACT Micromechanical analysis of ductile bulk metallic glasses at various temperatures and strain rates revealed accurate information on inhomogeneous flow kinetics. The disappearance of flow instabilities (i.e. serrations) at low temperatures correlates with a change from negative to positive strain-rate sensitivity and exhibits an activation energy of 0.37 eV. Based on these findings, a constitutive deformation model for thermally-activated flow in disordered systems is presented, which accounts for possible structural relaxation processes within the shear bands. Similarities in the flow behaviour of bulk metallic glasses with the Portevin-Le Châtelier effect known for crystalline metals are discussed.
Scripta Mater, 2005
ABSTRACT Tensile properties and microstructure of Danocrystalline electrodeposited Ni at temperat... more ABSTRACT Tensile properties and microstructure of Danocrystalline electrodeposited Ni at temperatures between room temperature and 330° C are presented. Above 300° C low flow stress and high tensile elongation are observed along with grain growth and segregation of sulphur to the grain boundaries causing the formation of a Ni-sulphide phase. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
International Journal of Earth Sciences, 2010
The Valais units in Savoy (Zone des Brèches de
Materials Processing Handbook, 2007
Physical Review Letters, 2011
In situ acoustic emission monitoring is shown to capture the initiation of shear bands in metalli... more In situ acoustic emission monitoring is shown to capture the initiation of shear bands in metallic glasses. A model picture is inferred from stick-slip flow in granular media such that the origin of acoustic emission is attributed to a mechanism of structural dilatation. By employing a quantitative approach, the critical volume change associated with shear-band initiation in a metallic glass is estimated to be a few percent only. This result agrees with typical values of excess free volume found in the supercooled liquid regime near the glass transition temperature.
Nanoscale, 2009
We present a method where epsilon-cobalt nanoparticles with an average diameter of 4.5 nm can be ... more We present a method where epsilon-cobalt nanoparticles with an average diameter of 4.5 nm can be synthesized in a controlled process and in significantly larger quantities than previously reported in the literature, based on the thermal decomposition of dicobaltoctacarbonyl in the presence of oleic acid and trioctylphosphine oxide (TOPO). Moreover, since the resulting particles are coated with an oleate layer, as shown by infrared (IR) spectroscopy, the colloids can be re-dispersed in organic solvents. These dispersions are suitable for the preparation of nanocomposites by a simple procedure, i.e. mixing of the cobalt dispersion with a polymer solution followed by casting and solvent evaporation. Magnetization measurements confirm the expected superparamagnetic behavior for both the cobalt nanoparticles and the metal-polymer nanocomposites.
Metallurgical and Materials Transactions A, 2007
The microstructure and texture of copper subjected to equal channel angular extrusion (ECAE) via ... more The microstructure and texture of copper subjected to equal channel angular extrusion (ECAE) via route B C for up to 16 passes have been assessed using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), X-ray diffraction (XRD) peak broadening, and texture analysis. The differences in grain size measured by these techniques allows for an understanding of microstructural evolution. A gradual decrease in grain size occurs with an increasing number of passes, while the subgrain size remains approximately constant. Up to four passes, the fraction of high-angle grain boundaries (HAGBs) (>15 deg) increases from 15 to 45 pct, but remains constant thereafter. The grain boundary character distribution shows a decrease of S1 boundaries and an increase of S3 boundaries with higher passes. After 16 passes, a few regions of large 1 to 4 lm sized grains embedded in a submicrometer sized matrix were observed. These agglomerates of larger grain diameters together with the measured decrease in the dislocation density correlate with the observed decrease in yield strength of samples subjected to four and more passes. Texture evolution is adequately described under conditions of negative simple shear. The effect of increased accumulated strain results in an overall spread of orientation densities due to the absence of stable end positions post-ECAE. Detailed microstructural information suggests that strengthening mechanisms in the material can be sufficiently well described by the classical Hall-Petch relationship by applying it to the subgrain size, while the subgrain size remains smaller than the grain size.
MATERIALS TRANSACTIONS, 2007
New findings on the inhomogeneous plastic deformation of bulk metallic glasses (BMGs) have shown ... more New findings on the inhomogeneous plastic deformation of bulk metallic glasses (BMGs) have shown a disappearance of serrated flow below a critical temperature or above a critical strain rate. This correlates with a change in the strain rate sensitivity (SRS) from negative to positive values, suggesting a change in the deformation mechanism. In addition, a change in the SRS correlating with the increase in the stress drop magnitude is observed with increasing strain. Results on the serration and flow dependence for the binary BMG Cu 50 Zr 50 show close phenomenological similarities with the Portevin -Le Châtelier or dynamic strain aging effect known for crystalline solids. An alternative model for the appearance and disappearance of serrated flow based on the structural relaxation of the atomic configuration of shear transformation zones is described. [
Materials Science and Engineering: A, 2006
Progressive texture evolution during the second pass of equal channel angular extrusion (ECAE) of... more Progressive texture evolution during the second pass of equal channel angular extrusion (ECAE) of copper via route B C was investigated by interrupting the extrusion and measuring the textures of seven sections starting within the entry channel, continuing through the die corner region, and ending within the exit channel. Experimental textures showed the development of {1 1 1} u v w θ and {h k l} 1 1 0 θ partial fibers; and that the most significant texture changes occurred near the die intersection plane. Consistent texture predictions were achieved by visco-plastic selfconsistent modelling (VPSC) using finite element (FE)-predicted deformation history. The FE simulation from the center of the billet cross-section indicated that the deviation of ECAE deformation from simple shear at the intersection of the die channels was not significant.
Materials Science and Engineering: A, 2006
Texture and microstructural evolution of interstitial-free (IF) steel and copper (Cu) subjected t... more Texture and microstructural evolution of interstitial-free (IF) steel and copper (Cu) subjected to room temperature equal channel angular extrusion for N = 1, 2 and 4 passes, route B C were compared. Both materials exhibit texture development similar to simple shear. Orientations of E {0 1 1} 1 1 1 and D {1 1 2} 1 1 1 type components are most prominent for IF-steel, while maximum intensities for A andĀ {1 1 1} 1 1 0 components were found in Cu. Quantitative texture and difference indices indicate a general increase up to the second pass followed by a decrease at the end of four passes. Following each pass, the five most dominant orientations were used to quantify the change in Taylor factor estimate for simulated uniaxial tensile deformation along the three principal deformation directions. The results show approximately equivalent estimates for both materials after four passes and reflect increasing microstructural homogeneity after a full 360 • revolution of the billet longitudinal axis. Transmission electron microscopy shows strongly aligned lamellar boundaries oriented along the major slip planes and directions of bcc and fcc structures. After four passes, the refined microstructure is characterised by an average subgrain size of ∼230 for IF-steel and ∼170 nm for Cu.
Journal of Materials Science, 2007
Journal of Materials Chemistry, 2012
... André R. Studart*a, Adrienne Nelsonb, Boris Iwanovskyb, Martin Kotyrbab, Andreas A. Kündigb, ... more ... André R. Studart*a, Adrienne Nelsonb, Boris Iwanovskyb, Martin Kotyrbab, Andreas A. Kündigb, Florian H. Dalla Torreb, Urs T. Gonzenbachc, Ludwig J. Gaucklerc and Jörg F. Löfflerb. ... 13, HJ Jin and J. Weissmuller, Adv. Eng. ...
Journal of Alloys and Compounds, 2010
At low homologous temperatures metallic glasses exhibit inhomogeneous flow behaviour, which is as... more At low homologous temperatures metallic glasses exhibit inhomogeneous flow behaviour, which is associated with narrow shear banding. Based on the width of the shear bands and the time-dependent heat conduction, we show here that this process is not fully adiabatic at low strain rates, even though temperatures are sufficiently high to create a drop in viscosity within either a new or a pre-existing shear band. Evaluation of the deformation kinetics at cryogenic temperatures suggests an increase in viscosity within the shear band, although temperatures are still sufficiently high to cause localised melting at fracture. In addition, a change from serrated to non-serrated flow can be observed if the temperature is lowered below a critical value. This macroscopic change in the flow behaviour is directly related to a change in the strain rate sensitivity from negative to positive values, suggesting a clear change in deformation behaviour. We propose a refined shear dilatation model to explain the experimental findings.
Applied Physics Letters, 2006
ABSTRACT Detailed investigations were carried out on the deformation behavior of Zr-based monolit... more ABSTRACT Detailed investigations were carried out on the deformation behavior of Zr-based monolithic bulk metallic glass and bulk metallic glass matrix composites. The latter, due to splitting and multiplication of shear bands, exhibits larger compressive strains than the former, without significant loss of strength. Serrated flow in conjunction with a negative strain rate sensitivity was observed in both materials. This observation, together with an increase in stress drops with increasing strain and their decrease with increasing strain rate, indicates phenomenologically close similarities with the dynamic strain aging deformation mechanism known for crystalline solids. The micromechanical mechanism of a shear event is discussed in light of these results.