E. Evangelista - Academia.edu (original) (raw)

Papers by E. Evangelista

Research paper thumbnail of A TEM study of the combined effect of severe plastic deformation and (Zr), (Sc+Zr)-containing dispersoids on an Al–Mg–Si alloy

Journal of Materials Science, 2006

... 2002) Acta Mater 50:4461 7. Horita Z, Fujinami T, Langdon TG (2001) Mater Sci Eng A318:34 8. ... more ... 2002) Acta Mater 50:4461 7. Horita Z, Fujinami T, Langdon TG (2001) Mater Sci Eng A318:34 8. Segal VM, Reznikov VI, Drobyshevskiy AE, Kopylov VI (1981) Russ Metall 1 ... Matsuda K, Gamada H, Fuji K, Uteni Y, Sato T, Kamis A, Ikeno S (1998) Metall Mater Trans A29:1161 34. ...

Research paper thumbnail of Characterisation of a 6082 Aluminum Alloy after Thixoforming

Key Engineering Materials, 2000

... 6082 (bars) 30-/ '/ / 20 - w 10 J II r r-i г—i—i' м mi ■ ■)" i'i ... cert... more ... 6082 (bars) 30-/ '/ / 20 - w 10 J II r r-i г—i—i' м mi ■ ■)" i'i ... certain difficulty, due to the narrow window of temperatures above 595°C in which the solid a-phase ... free component, the tensile strength) by means of proper heat treatments, the same normally used for extrusion alloys. ...

Research paper thumbnail of Dynamic recovery and strain hardening in the hot deformation of type 317 stainless steel

Materials Science and Engineering, 1986

ABSTRACT

Research paper thumbnail of A study of the hot formability of an Al-Cu-Mg-Zr alloy

ABSTRACT The high-temperature plasticity of a Zr-stabilised 2014 aluminium alloy was investigated... more ABSTRACT The high-temperature plasticity of a Zr-stabilised 2014 aluminium alloy was investigated in a wide range of temperatures and strain rates. The microstructure of representative torsioned samples was analysed by transmission electron microscopy, and the characteristics of particle and precipitate distribution were quantitatively estimated. The strain-rate dependence on stress and temperature was analysed by means of the conventional constitutive equations used for describing hot-working behaviour as well as a modified form of the sinh equation, where the stress was substituted by an effective stress, i.e., by the difference between the stress and a threshold stress. This temperature-dependent threshold stress was found to be a fraction of the Orowan stress generated by precipitates increasing from 62 to 94% as temperature decreased from 773 to 573 K.

Research paper thumbnail of Semi-solid thermal transformations of Al−Si alloys and the resulting mechanical properties

This study demonstrated that 356/357 type Al−Si alloys cast with high solidification rates result... more This study demonstrated that 356/357 type Al−Si alloys cast with high solidification rates resulting in a fine grain structure could be rapidly thermally transformed into a structure suitable for semi-solid forming. The mechanical properties of these alloys were comparable to those of electromagnetically stirred semi-solid as well as the as-cast properties.

Research paper thumbnail of Transmission Electron Microscopy Study of Strain-Induced Low- and High-Angle Boundary Development in Equal-Channel Angular-Pressed Commercially Pure Aluminum

Metallurgical and Materials Transactions A, 2008

The evolution of the microstructure in a commercially pure aluminum during equal channel angular ... more The evolution of the microstructure in a commercially pure aluminum during equal channel angular pressing (ECAP) using route BC was investigated by transmission electron microscopy. Subgrains, or cells, form, which have both high (ϕ > 15 deg) and low (ϕ < 15 deg) misorientation. Misorientations and spacings of cell boundaries were determined from about 250 boundaries per pass of ECAP cell boundaries on the basis of Kikuchi patterns and Moiré fringes. The average cell size and misorientation saturate within the first two passes. Misorientations and spacings of high-angle boundaries decrease with the number of passes. After eight passes, the cell size is ≈1.3 μm and the fraction of high-angle boundaries is ≈0.7. The marked differences in the rate of grain structure evolution per pass are linked to differences in the ability of dislocations introduced in new passes to recombine with the existing ones. With increasing ECAP strain, the distribution of misorientations develops strong deviations from the MacKenzie distribution for statistical grain orientation. This is interpreted as a result of the tendency to form equiaxed grains in a textured grain structure.

Research paper thumbnail of Isothermal forging of AA2618 + 20% Al2O3 by means of hot torsion and hot compression tests

Materials Science and Engineering: A, 2004

The isothermal forming of AA2618 + 20% Al 2 O 3 was studied by employing hot torsion and hot comp... more The isothermal forming of AA2618 + 20% Al 2 O 3 was studied by employing hot torsion and hot compression tests in the temperature and strain rate ranges of 350-500 • C and 10-3-1 s-1 strain rate, respectively. The processing and stability maps of the material were calculated following the dynamic material model leading to identification of the best forming conditions. The constitutive equations were calculated for the studied material and the damage produced by forming operation was calculated in all the test conditions. Both optical and scanning electron microscopy were used to evaluate the microstructural evolution of the material.

Research paper thumbnail of Serrated grain boundaries in hot-worked aluminum alloys at high strains

Materials Characterization, 1995

ABSTRACT

Research paper thumbnail of Isothermal forging of metal matrix composites: Recrystallization behaviour by means of deformation efficiency

Composites Science and Technology, 2006

... Isothermal forging of metal matrix composites: Recrystallization behaviour by means of deform... more ... Isothermal forging of metal matrix composites: Recrystallization behaviour by means of deformation efficiency. ... A development of the map concept was obtained by Raj [2], who examined two important damage mechanisms in 6061 aluminium alloy reinforced with different ...

Research paper thumbnail of Influence of severe plastic deformations on secondary phase precipitation in a 6082 Al-Mg-Si alloy

Metallurgical and Materials Transactions A, 2005

The role of severe plastic deformation on the second-phase stability in a 6082 Al-Mg-Si alloy was... more The role of severe plastic deformation on the second-phase stability in a 6082 Al-Mg-Si alloy was studied using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. The alloy was fully annealed prior to undergoing up to six equal channel angular pressing (ECAP) passes using route C. The Orowan strengthening mechanism was calculated on the basis of TEM inspections for the two hardening second-phase precipitates: Mg 2 Si and Si. The former had a major tendency to be cut and fragmented by dislocations, while in the latter, a dissolution process was induced by severe plastic deformation. Accordingly, the second-phase Si particles became progressively less effective with increasing deformation (i.e., additional ECAP passes). The increase in hardness with the ECAP passes was mostly due to the grain refining mechanism and to dislocation tangles within the newly formed grains. The expected, though if limited, contribution of second-phase hardening was prevalently accounted for by the Mg 2 Si particles.

Research paper thumbnail of A TEM study of the combined effect of severe plastic deformation and (Zr), (Sc+Zr)-containing dispersoids on an Al–Mg–Si alloy

Journal of Materials Science, 2006

... 2002) Acta Mater 50:4461 7. Horita Z, Fujinami T, Langdon TG (2001) Mater Sci Eng A318:34 8. ... more ... 2002) Acta Mater 50:4461 7. Horita Z, Fujinami T, Langdon TG (2001) Mater Sci Eng A318:34 8. Segal VM, Reznikov VI, Drobyshevskiy AE, Kopylov VI (1981) Russ Metall 1 ... Matsuda K, Gamada H, Fuji K, Uteni Y, Sato T, Kamis A, Ikeno S (1998) Metall Mater Trans A29:1161 34. ...

Research paper thumbnail of Characterisation of a 6082 Aluminum Alloy after Thixoforming

Key Engineering Materials, 2000

... 6082 (bars) 30-/ '/ / 20 - w 10 J II r r-i г—i—i' м mi ■ ■)" i'i ... cert... more ... 6082 (bars) 30-/ '/ / 20 - w 10 J II r r-i г—i—i' м mi ■ ■)" i'i ... certain difficulty, due to the narrow window of temperatures above 595°C in which the solid a-phase ... free component, the tensile strength) by means of proper heat treatments, the same normally used for extrusion alloys. ...

Research paper thumbnail of Dynamic recovery and strain hardening in the hot deformation of type 317 stainless steel

Materials Science and Engineering, 1986

ABSTRACT

Research paper thumbnail of A study of the hot formability of an Al-Cu-Mg-Zr alloy

ABSTRACT The high-temperature plasticity of a Zr-stabilised 2014 aluminium alloy was investigated... more ABSTRACT The high-temperature plasticity of a Zr-stabilised 2014 aluminium alloy was investigated in a wide range of temperatures and strain rates. The microstructure of representative torsioned samples was analysed by transmission electron microscopy, and the characteristics of particle and precipitate distribution were quantitatively estimated. The strain-rate dependence on stress and temperature was analysed by means of the conventional constitutive equations used for describing hot-working behaviour as well as a modified form of the sinh equation, where the stress was substituted by an effective stress, i.e., by the difference between the stress and a threshold stress. This temperature-dependent threshold stress was found to be a fraction of the Orowan stress generated by precipitates increasing from 62 to 94% as temperature decreased from 773 to 573 K.

Research paper thumbnail of Semi-solid thermal transformations of Al−Si alloys and the resulting mechanical properties

This study demonstrated that 356/357 type Al−Si alloys cast with high solidification rates result... more This study demonstrated that 356/357 type Al−Si alloys cast with high solidification rates resulting in a fine grain structure could be rapidly thermally transformed into a structure suitable for semi-solid forming. The mechanical properties of these alloys were comparable to those of electromagnetically stirred semi-solid as well as the as-cast properties.

Research paper thumbnail of Transmission Electron Microscopy Study of Strain-Induced Low- and High-Angle Boundary Development in Equal-Channel Angular-Pressed Commercially Pure Aluminum

Metallurgical and Materials Transactions A, 2008

The evolution of the microstructure in a commercially pure aluminum during equal channel angular ... more The evolution of the microstructure in a commercially pure aluminum during equal channel angular pressing (ECAP) using route BC was investigated by transmission electron microscopy. Subgrains, or cells, form, which have both high (ϕ > 15 deg) and low (ϕ < 15 deg) misorientation. Misorientations and spacings of cell boundaries were determined from about 250 boundaries per pass of ECAP cell boundaries on the basis of Kikuchi patterns and Moiré fringes. The average cell size and misorientation saturate within the first two passes. Misorientations and spacings of high-angle boundaries decrease with the number of passes. After eight passes, the cell size is ≈1.3 μm and the fraction of high-angle boundaries is ≈0.7. The marked differences in the rate of grain structure evolution per pass are linked to differences in the ability of dislocations introduced in new passes to recombine with the existing ones. With increasing ECAP strain, the distribution of misorientations develops strong deviations from the MacKenzie distribution for statistical grain orientation. This is interpreted as a result of the tendency to form equiaxed grains in a textured grain structure.

Research paper thumbnail of Isothermal forging of AA2618 + 20% Al2O3 by means of hot torsion and hot compression tests

Materials Science and Engineering: A, 2004

The isothermal forming of AA2618 + 20% Al 2 O 3 was studied by employing hot torsion and hot comp... more The isothermal forming of AA2618 + 20% Al 2 O 3 was studied by employing hot torsion and hot compression tests in the temperature and strain rate ranges of 350-500 • C and 10-3-1 s-1 strain rate, respectively. The processing and stability maps of the material were calculated following the dynamic material model leading to identification of the best forming conditions. The constitutive equations were calculated for the studied material and the damage produced by forming operation was calculated in all the test conditions. Both optical and scanning electron microscopy were used to evaluate the microstructural evolution of the material.

Research paper thumbnail of Serrated grain boundaries in hot-worked aluminum alloys at high strains

Materials Characterization, 1995

ABSTRACT

Research paper thumbnail of Isothermal forging of metal matrix composites: Recrystallization behaviour by means of deformation efficiency

Composites Science and Technology, 2006

... Isothermal forging of metal matrix composites: Recrystallization behaviour by means of deform... more ... Isothermal forging of metal matrix composites: Recrystallization behaviour by means of deformation efficiency. ... A development of the map concept was obtained by Raj [2], who examined two important damage mechanisms in 6061 aluminium alloy reinforced with different ...

Research paper thumbnail of Influence of severe plastic deformations on secondary phase precipitation in a 6082 Al-Mg-Si alloy

Metallurgical and Materials Transactions A, 2005

The role of severe plastic deformation on the second-phase stability in a 6082 Al-Mg-Si alloy was... more The role of severe plastic deformation on the second-phase stability in a 6082 Al-Mg-Si alloy was studied using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. The alloy was fully annealed prior to undergoing up to six equal channel angular pressing (ECAP) passes using route C. The Orowan strengthening mechanism was calculated on the basis of TEM inspections for the two hardening second-phase precipitates: Mg 2 Si and Si. The former had a major tendency to be cut and fragmented by dislocations, while in the latter, a dissolution process was induced by severe plastic deformation. Accordingly, the second-phase Si particles became progressively less effective with increasing deformation (i.e., additional ECAP passes). The increase in hardness with the ECAP passes was mostly due to the grain refining mechanism and to dislocation tangles within the newly formed grains. The expected, though if limited, contribution of second-phase hardening was prevalently accounted for by the Mg 2 Si particles.