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Papers by Jagga R Gatti

Research paper thumbnail of Microstructure and Texture of Al-2.5wt.%Mg Processed by Combining Accumulative Roll Bonding and Conventional Rolling

Journal of Materials Engineering and Performance, 2014

Research paper thumbnail of Nucleation behavior and formation of recrystallization texture in pre-recovery treated heavily cold and warm-rolled Al–2.5 wt.%Mg alloy

Materials Characterization, 2015

ABSTRACT Evolution of cube texture after annealing was investigated in severely cold and warm-rol... more ABSTRACT Evolution of cube texture after annealing was investigated in severely cold and warm-rolled Al–2.5 wt.%Mg alloy without and with prior recovery treatments. The alloy was cold and warm-rolled at room temperature and at 473 K (200 °C), respectively, to 97% reduction in thickness and annealed at different temperatures ranging from 548 K (275 °C) to 673 K (400 °C). The warm-rolled material showed much stronger and sharper cube texture as compared to the cold-rolled material after different annealing treatments. However, prior recovery treatments at 473 K (200 °C) significantly diminished the strength of the cube texture in the warm-rolled material after annealing. In contrast, the strength of the cube component after annealing in the cold-rolled material was not significantly affected by the prior recovery treatments. The observed differences could be adequately explained by the preferential recovery and nucleation behavior of cube grains in different treated conditions.

Research paper thumbnail of Annealing textures of severely cold and warm-rolled Al–2.5 wt.%Mg alloy

Journal of Alloys and Compounds, 2014

Abstract The evolution of recrystallization texture was investigated in severely deformed Al–2.5 ... more Abstract The evolution of recrystallization texture was investigated in severely deformed Al–2.5 wt.%Mg alloy. For this purpose the alloy was cold and warm-rolled to 97% reduction in thickness at room temperature and 473 K (200 °C), respectively, using a combination of accumulative roll bonding and conventional rolling. The deformed materials were annealed at temperatures ranging between 473 K (200 °C) and 673 K (400 °C). The deformed materials showed fine lamellar structure and strong copper type texture. However, the warm-rolled material showed much stronger cube texture ({1 0 0}〈0 0 1〉) after different annealing treatments. Orientations of early recrystallized grains in partially recrystallized materials obtained after annealing for short duration revealed strong tendency for preferential nucleation of cube grains in warm-rolled as compared to the cold-rolled material. The observed preferential nucleation of cube oriented grains in warm-rolled material was attributed to more recovered structure of cube oriented grains. In contrast, strong pinning of dislocations by solute Mg atoms during cold-rolling at room temperature inhibited the recovery of cube grains and greatly diminished their preferential nucleation. The cube component was significantly strengthened with increasing annealing temperature in both cold and warm-rolled materials due to the growth of the cube grains.

Research paper thumbnail of Effect of Prior Recovery Treatment on the Evolution of Cube Texture During Annealing of Severely Warm-Rolled Al-2.5 wt pctMg Alloy

Metallurgical and Materials Transactions A, 2015

Research paper thumbnail of Effect of Change in Strain Path During Cold Rolling on the Evolution of Microstructure and Texture in Al and Al-2.5%Mg

Journal of Materials Engineering and Performance, 2013

ABSTRACT The effect of change in strain path during cold rolling on the evolution of microstructu... more ABSTRACT The effect of change in strain path during cold rolling on the evolution of microstructure and texture is investigated. For this purpose, high purity aluminum and Al-2.5%Mg alloy are deformed (~90% reduction in thickness) by unidirectional and cross cold rolling. Irrespective of the alloy system, copper-type texture is observed in unidirectional processed materials, while strong brass ({011}〈112〉) texture is developed during cross rolling. Unidirectionally rolled aluminum showed higher HAGB fraction, but similar HAGB spacing as compared to the cross-rolled aluminum after 90% reduction in thickness. At the same time, the internal misorientation in the cross-rolled 2N-Al is higher than in the unidirectionally rolled material. In contrast, Al-2.5% Mg alloy processed differently in both ways shows similar HAGB fraction, spacing, and internal misorientation distribution. These observations indicate that microstructure evolution due to strain path change is more strongly affected by dynamic recovery as compared to texture evolution.

Research paper thumbnail of Texture Evolution During Cross Rolling and Annealing of High-Purity Nickel

Metallurgical and Materials Transactions A, 2013

ABSTRACT Evolution of texture during cross rolling and subsequent annealing was studied in high-p... more ABSTRACT Evolution of texture during cross rolling and subsequent annealing was studied in high-purity nickel. For this purpose nickel samples were subjected to multipass cross rolling up to 90 pct reduction in thickness followed by annealing at different temperatures ranging between 673 K and 1073 K (400 °C and 800 °C). Cross rolling was carried out by rotating the samples about the normal direction (ND) by 90 deg interchanging the rolling direction and transverse direction (TD) between each consecutive pass. The development of microstructure and texture was characterized using X-ray and electron backscattered diffraction (EBSD) techniques. The deformation texture was characterized by the presence of strong brass ({110}〈112〉) and ND-rotated brass ({011}〈21 $ \overline{13} $ 13〉)) orientations. Upon annealing at 673 K (400 °C), ND||[111] fiber could be observed in the microtexture which originated from the twin formation of the recrystallized TD-rotated cube ({027}〈0 $ \overline{7} $ 2〉) grains. The fiber was weakened after annealing at 1073 K (800 °C) because of the decreased propensity for twin formation, and the microtexture was found to be weak and diffused. EBSD studies on early recrystallization stages indicated the absence of preferential nucleation of cube grains being in agreement with a weak cube texture formation in annealed cross-rolled high-purity nickel.

Research paper thumbnail of Evolution of microstructure and texture during annealing of Al-2.5%Mg-0.2%Sc severely deformed by a combination of accumulative roll bonding (ARB) and conventional rolling.

Evolution of microstructure and texture during heavy cold-rolling and annealing of Al-2.5%Mg-0.2%... more Evolution of microstructure and texture during heavy cold-rolling and annealing of Al-2.5%Mg-0.2%Sc alloy was investigated. For this purpose recrystallized sheets of 1mm
thickness having finely dispersed precipitates were processed to 3 cycles of ARB (equivalent strain, εeq=2.4) followed by conventional rolling to a final thickness of 200µm resulting in total equivalent strain of 4.0. Evolution of ultrafine microstructure and strong copper or pure metal
type texture were observed during deformation. During annealing very stable microstructure was observed up to 400˚C but further annealing resulted in formation of a layered
microstructure with deformed layer sandwiched between recrystallized layers. Formation of strong cube texture is not observed in the recrystallized layers. Isothermal annealing for longer time at 500°C leads to abnormal growth of Q orientation ({013}<213>) within the deformed layer.

Research paper thumbnail of EVOLUTION OF MICROSTRUCTURE AND TEXTURE DURING SEVERE COLD ROLLING AND ANNEALING OF Al-2.5%Mg AND Al-2.5%Mg-0.2%Sc ALLOYS

Evolution of microstructure and texture in Al-2.5%Mg and Al- 2.5%Mg-0.2%Sc alloys during severe c... more Evolution of microstructure and texture in Al-2.5%Mg and Al-
2.5%Mg-0.2%Sc alloys during severe cold rolling and subsequent annealing was studied using electron back scatter diffraction (EBSD). These alloys were first thermo-mechanically processed to sheets of average thickness (~1mm) with well recrystallized microstructures. These sheets were subsequently severely coldrolled up to an equivalent strain of 4.32 using a combination of Accumulative Roll Bonding and conventional cold-rolling. The deformed alloys were subjected to isochronal annealing treatment for one hour in a wide temperature range. Development of Ultrafine lamellar microstructure subdivided by high angle grain boundaries (HAGB) and pure metal or copper type texture was observed in both the alloys during deformation. Al-Mg-Sc consistently showed higher hardness as compared to the Al-Mg.
Al-Mg recrystallized around ~ 2500C but in Al-Mg-Sc the
recrystallization was greatly delayed up to 500°C and the
deformation texture components were retained during annealing. The differences in the recrystallization behavior of two materials were discussed with regard to the deformation microstructure and presence of fine precipitates.

Research paper thumbnail of Texture Evolution During Cross Rolling and Annealing of High-Purity Nickel

Evolution of texture during cross rolling and subsequent annealing was studied in high-purity nic... more Evolution of texture during cross rolling and subsequent annealing was studied in high-purity nickel. For this purpose nickel samples were subjected to multipass cross rolling up to 90 pct reduction in thickness followed by annealing at different temperatures ranging between 673 K and 1073 K (400 °C and 800 °C). Cross rolling was carried out by rotating the samples about the normal direction (ND) by 90 deg interchanging the rolling direction and transverse direction (TD) between each consecutive pass. The development of microstructure and texture was characterized using X-ray and electron backscattered diffraction (EBSD) techniques. The deformation texture was characterized by the presence of strong brass ({110}h112i) and ND-rotated brass ({011}h211313i)) orientations. Upon annealing at 673 K (400 °C), ND||[111] fiber could be observed in the microtexture which originated from the twin formation of the recrystallized TD-rotated cube ({027}h072i) grains. The fiber was weakened after annealing at 1073 K (800 °C) because of the decreased propensity for twin formation, and the microtexture was found to be weak and diffused. EBSD studies on early recrystallization stages indicated the absence of preferential nucleation of cube grains being in agreement with a weak cube texture formation in annealed cross-rolled high-purity nickel.

Research paper thumbnail of Effect of Change in Strain Path During Cold Rolling on the Evolution of Microstructure and Texture in Al and Al-2.5%Mg

The effect of change in strain path during cold rolling on the evolution of microstructure and te... more The effect of change in strain path during cold rolling on the evolution of microstructure and texture is investigated. For this purpose, high purity aluminum and Al-2.5%Mg alloy are deformed ($90% reduction in thickness) by unidirectional and cross cold rolling. Irrespective of the alloy system, copper-type texture is observed in unidirectional processed materials, while strong brass ({011}AE112ae) texture is developed during cross rolling. Unidirectionally rolled aluminum showed higher HAGB fraction, but similar HAGB spacing as compared to the cross-rolled aluminum after 90% reduction in thickness. At the same time, the internal misorientation in the cross-rolled 2N-Al is higher than in the unidirectionally rolled material. In contrast, Al-2.5% Mg alloy processed differently in both ways shows similar HAGB fraction, spacing, and internal misorientation distribution. These observations indicate that microstructure evolution due to strain path change is more strongly affected by dynamic recovery as compared to texture evolution.

Research paper thumbnail of Microstructure and texture evolution during annealing of equiatomic CoCrFeMnNi high-entropy alloy

Evolution of microstructure and texture after heavy cold rolling and subsequent annealing in a wi... more Evolution of microstructure and texture after heavy cold rolling and subsequent annealing in a wide temperature range was first studied in an FCC equiatomic CoCrFeMnNi high-entropy alloy (HEA). Development of a submicron-cell structure and a strong brass-type texture was observed after 90% cold rolling. An ultra-fine microstructure having average recrystallized grain size $1 lm with profuse annealing twins was observed after annealing at 650 °C. Remarkable resistance against grain coarsening was observed at least up to 800 °C. The mechanisms for these features were closely related with the distinct whole-solute matrix in HEAs. The recrystallization texture was characterized by the retention of deformation texture components similar to those of TWIP and 316 stainless steels. But notable differences exist. The S ({1 2 3}h6 3 4i) component is stronger than brass ({1 1 0}h1 1 2i) and Goss ({1 1 0}h0 0 1i), and strengthened with increasing annealing temperatures. Strong a-fiber (h1 1 0i//ND) components other than the deformation components B S and G, and higher fraction of random components also develop. It could be attributed to profuse annealing twin formation due to the low stacking fault energy of the alloy.

Research paper thumbnail of Nucleation behavior and formation of recrystallization texture in pre-recovery treated heavily cold and warm-rolled Al–2.5 wt.%Mg alloy

Evolution of cube texture after annealing was investigated in severely cold and warm-rolled Al–2.... more Evolution of cube texture after annealing was investigated in severely cold and warm-rolled Al–2.5 wt.%Mg alloy without and with prior recovery treatments. The alloy was cold and warm-rolled at room temperature and at 473 K (200 °C), respectively, to 97% reduction in thickness and annealed at different temperatures ranging from 548 K (275 °C) to 673 K (400 °C). The warm-rolled material showed much stronger and sharper cube texture as compared to the cold-rolled material after different annealing treatments. However, prior recovery treatments at 473 K (200 °C) significantly diminished the strength of the cube texture in the warm-rolled material after annealing. In contrast, the strength of the cube component after annealing in the cold-rolled material was not significantly affected by the prior recovery treatments. The observed differences could be adequately explained by the preferential recovery and nucleation behavior of cube grains in different treated conditions.

Research paper thumbnail of Effect of Prior Recovery Treatment on the Evolution of Cube Texture During Annealing of Severely Warm-Rolled Al-2.5 wt pctMg Alloy

The effect of prior recovery on the evolution of cube texture ({001}h100i) in severely warm-rolle... more The effect of prior recovery on the evolution of cube texture ({001}h100i) in severely warm-rolled and annealed Al-2.5 wt pctMg alloy was studied. The Al-2.5 wt pctMg alloy was warm rolled to 97 pct reduction in thickness at 473 K (200 °C). The warm-rolled sheets were isochronally annealed for 1 hour at temperatures ranging from 523 K to 673 K (250 °C to 400 °C) without and with prior recovery treatments. In case of prior recovery, the sheets were pre-treated at 473 K (200 °C) for different time intervals ranging from 3.6 9 10 3 seconds (1 hour) to 8.64 9 10 4 seconds (24 hours) before the annealing. The warm-rolled alloy showed finely subdivided lamellar structure and strong presence of pure metal type texture. The annealed materials without any prior recovery treatment showed strong cube texture after annealing which could be attributed to the oriented nucleation of cube grains resulting from the preferentially recovered structure of cube regions in the warm-rolled state. In contrast, the cube texture was significantly weakened in materials subjected to different prior recovery treatments. The prior recovery treatments resulted in homogenous recovery which was confirmed by microstructural, textural, and conductivity measurements. Homogenous recovery eliminated the nucleation advantage of cube regions originating from the preferentially recovered structure and weakened the cube texture significantly. The present results indicated that prior recovery treatment could be effectively used to control recrystallization cube texture in severely warm-rolled aluminum alloys.

Research paper thumbnail of Microstructure and Texture of Al-2.5wt.%Mg Processed by Combining Accumulative Roll Bonding and Conventional Rolling

Evolution of microstructure and texture during severe deformation and annealing was studied in Al... more Evolution of microstructure and texture during severe deformation and annealing was studied in Al-2.5%Mg alloy processed by two different routes, namely, monotonic Accumulative Roll Bonding (ARB) and a hybrid route combining ARB and conventional rolling (CR). For this purpose Al-2.5%Mg sheets were subjected to 5 cycles of monotonic ARB (equivalent strain (e eq) = 4.0) processing while in the hybrid route (ARB + CR) 3 cycle ARB-processed sheets were further deformed by conventional rolling to 75% reduction in thickness (e eq = 4.0). Although formation of ultrafine structure was observed in the two processing routes, the monotonic ARB—processed material showed finer microstructure but weak texture as compared to the ARB + CR—processed material. After complete recrystallization, the ARB + CR-processed material showed weak cube texture ({001}AE100ae) but the cube component was almost negligible in the monotonic ARB-processed material-processed material. However, the ND-rotated cube components were stronger in the monotonic ARB-processed material-processed material. The observed differences in the microstructure and texture evolution during deformation and annealing could be explained by the characteristic differences of the two processing routes.

Research paper thumbnail of Annealing textures of severely cold and warm-rolled Al–2.5 wt.%Mg alloy

The evolution of recrystallization texture was investigated in severely deformed Al–2.5 wt.%Mg al... more The evolution of recrystallization texture was investigated in severely deformed Al–2.5 wt.%Mg alloy. For this purpose the alloy was cold and warm-rolled to 97% reduction in thickness at room temperature and 473 K (200 °C), respectively, using a combination of accumulative roll bonding and conventional rolling. The deformed materials were annealed at temperatures ranging between 473 K (200 °C) and 673 K (400 °C). The deformed materials showed fine lamellar structure and strong copper type texture. However , the warm-rolled material showed much stronger cube texture ({1 0 0}h0 01i) after different anneal-ing treatments. Orientations of early recrystallized grains in partially recrystallized materials obtained after annealing for short duration revealed strong tendency for preferential nucleation of cube grains in warm-rolled as compared to the cold-rolled material. The observed preferential nucleation of cube oriented grains in warm-rolled material was attributed to more recovered structure of cube oriented grains. In contrast, strong pinning of dislocations by solute Mg atoms during cold-rolling at room temperature inhibited the recovery of cube grains and greatly diminished their preferential nucleation. The cube component was significantly strengthened with increasing annealing temperature in both cold and warm-rolled materials due to the growth of the cube grains.

Conference Presentations by Jagga R Gatti

Research paper thumbnail of Microstructure, Texture and Hardness Properties of Bulk Ultrafinegrained Al-2.5%Mg and Al-2.5%Mg-0.2%Sc Alloys Processed by Accumulative Roll Bonding (ARB

Evolution of microstructure, texture and hardness properties during severe plastic deformation by... more Evolution of microstructure, texture and hardness properties during severe plastic deformation by accumulative roll bonding (ARB) was studied in Al-2.5%Mg and Al-2.5%Mg-0.2%Sc alloys using electron back scatter diffraction (EBSD) and micro hardness tester. Sheets of these alloys having 1 mm thickness were processed up to 7 cycles of ARB at room temperature corresponding to an accumulated equivalent strain (ɛ eq) of 5.6. Ultrafine lamellar microstructure with interlamellar spacing less than 400nm finely subdivided by high angle boundaries (misorientation angle >15°) was observed in both the alloys. Development of a strong β–fiber rolling texture could be observed in both alloys from the EBSD measurements. The hardness was found to increase monotonically with increasing number of ARB cycles in both materials. The key effect of Sc alloying was revealed by consistently higher hardness in Al-Mg-Sc as compared to the Al-Mg at all deformation levels. The increase in hardness in Al-Mg-Sc could be attributed to the presence of very fine Al 3 Sc precipitates in the starting material.

Research paper thumbnail of Microstructure and Texture of Al-2.5wt.%Mg Processed by Combining Accumulative Roll Bonding and Conventional Rolling

Journal of Materials Engineering and Performance, 2014

Research paper thumbnail of Nucleation behavior and formation of recrystallization texture in pre-recovery treated heavily cold and warm-rolled Al–2.5 wt.%Mg alloy

Materials Characterization, 2015

ABSTRACT Evolution of cube texture after annealing was investigated in severely cold and warm-rol... more ABSTRACT Evolution of cube texture after annealing was investigated in severely cold and warm-rolled Al–2.5 wt.%Mg alloy without and with prior recovery treatments. The alloy was cold and warm-rolled at room temperature and at 473 K (200 °C), respectively, to 97% reduction in thickness and annealed at different temperatures ranging from 548 K (275 °C) to 673 K (400 °C). The warm-rolled material showed much stronger and sharper cube texture as compared to the cold-rolled material after different annealing treatments. However, prior recovery treatments at 473 K (200 °C) significantly diminished the strength of the cube texture in the warm-rolled material after annealing. In contrast, the strength of the cube component after annealing in the cold-rolled material was not significantly affected by the prior recovery treatments. The observed differences could be adequately explained by the preferential recovery and nucleation behavior of cube grains in different treated conditions.

Research paper thumbnail of Annealing textures of severely cold and warm-rolled Al–2.5 wt.%Mg alloy

Journal of Alloys and Compounds, 2014

Abstract The evolution of recrystallization texture was investigated in severely deformed Al–2.5 ... more Abstract The evolution of recrystallization texture was investigated in severely deformed Al–2.5 wt.%Mg alloy. For this purpose the alloy was cold and warm-rolled to 97% reduction in thickness at room temperature and 473 K (200 °C), respectively, using a combination of accumulative roll bonding and conventional rolling. The deformed materials were annealed at temperatures ranging between 473 K (200 °C) and 673 K (400 °C). The deformed materials showed fine lamellar structure and strong copper type texture. However, the warm-rolled material showed much stronger cube texture ({1 0 0}〈0 0 1〉) after different annealing treatments. Orientations of early recrystallized grains in partially recrystallized materials obtained after annealing for short duration revealed strong tendency for preferential nucleation of cube grains in warm-rolled as compared to the cold-rolled material. The observed preferential nucleation of cube oriented grains in warm-rolled material was attributed to more recovered structure of cube oriented grains. In contrast, strong pinning of dislocations by solute Mg atoms during cold-rolling at room temperature inhibited the recovery of cube grains and greatly diminished their preferential nucleation. The cube component was significantly strengthened with increasing annealing temperature in both cold and warm-rolled materials due to the growth of the cube grains.

Research paper thumbnail of Effect of Prior Recovery Treatment on the Evolution of Cube Texture During Annealing of Severely Warm-Rolled Al-2.5 wt pctMg Alloy

Metallurgical and Materials Transactions A, 2015

Research paper thumbnail of Effect of Change in Strain Path During Cold Rolling on the Evolution of Microstructure and Texture in Al and Al-2.5%Mg

Journal of Materials Engineering and Performance, 2013

ABSTRACT The effect of change in strain path during cold rolling on the evolution of microstructu... more ABSTRACT The effect of change in strain path during cold rolling on the evolution of microstructure and texture is investigated. For this purpose, high purity aluminum and Al-2.5%Mg alloy are deformed (~90% reduction in thickness) by unidirectional and cross cold rolling. Irrespective of the alloy system, copper-type texture is observed in unidirectional processed materials, while strong brass ({011}〈112〉) texture is developed during cross rolling. Unidirectionally rolled aluminum showed higher HAGB fraction, but similar HAGB spacing as compared to the cross-rolled aluminum after 90% reduction in thickness. At the same time, the internal misorientation in the cross-rolled 2N-Al is higher than in the unidirectionally rolled material. In contrast, Al-2.5% Mg alloy processed differently in both ways shows similar HAGB fraction, spacing, and internal misorientation distribution. These observations indicate that microstructure evolution due to strain path change is more strongly affected by dynamic recovery as compared to texture evolution.

Research paper thumbnail of Texture Evolution During Cross Rolling and Annealing of High-Purity Nickel

Metallurgical and Materials Transactions A, 2013

ABSTRACT Evolution of texture during cross rolling and subsequent annealing was studied in high-p... more ABSTRACT Evolution of texture during cross rolling and subsequent annealing was studied in high-purity nickel. For this purpose nickel samples were subjected to multipass cross rolling up to 90 pct reduction in thickness followed by annealing at different temperatures ranging between 673 K and 1073 K (400 °C and 800 °C). Cross rolling was carried out by rotating the samples about the normal direction (ND) by 90 deg interchanging the rolling direction and transverse direction (TD) between each consecutive pass. The development of microstructure and texture was characterized using X-ray and electron backscattered diffraction (EBSD) techniques. The deformation texture was characterized by the presence of strong brass ({110}〈112〉) and ND-rotated brass ({011}〈21 $ \overline{13} $ 13〉)) orientations. Upon annealing at 673 K (400 °C), ND||[111] fiber could be observed in the microtexture which originated from the twin formation of the recrystallized TD-rotated cube ({027}〈0 $ \overline{7} $ 2〉) grains. The fiber was weakened after annealing at 1073 K (800 °C) because of the decreased propensity for twin formation, and the microtexture was found to be weak and diffused. EBSD studies on early recrystallization stages indicated the absence of preferential nucleation of cube grains being in agreement with a weak cube texture formation in annealed cross-rolled high-purity nickel.

Research paper thumbnail of Evolution of microstructure and texture during annealing of Al-2.5%Mg-0.2%Sc severely deformed by a combination of accumulative roll bonding (ARB) and conventional rolling.

Evolution of microstructure and texture during heavy cold-rolling and annealing of Al-2.5%Mg-0.2%... more Evolution of microstructure and texture during heavy cold-rolling and annealing of Al-2.5%Mg-0.2%Sc alloy was investigated. For this purpose recrystallized sheets of 1mm
thickness having finely dispersed precipitates were processed to 3 cycles of ARB (equivalent strain, εeq=2.4) followed by conventional rolling to a final thickness of 200µm resulting in total equivalent strain of 4.0. Evolution of ultrafine microstructure and strong copper or pure metal
type texture were observed during deformation. During annealing very stable microstructure was observed up to 400˚C but further annealing resulted in formation of a layered
microstructure with deformed layer sandwiched between recrystallized layers. Formation of strong cube texture is not observed in the recrystallized layers. Isothermal annealing for longer time at 500°C leads to abnormal growth of Q orientation ({013}<213>) within the deformed layer.

Research paper thumbnail of EVOLUTION OF MICROSTRUCTURE AND TEXTURE DURING SEVERE COLD ROLLING AND ANNEALING OF Al-2.5%Mg AND Al-2.5%Mg-0.2%Sc ALLOYS

Evolution of microstructure and texture in Al-2.5%Mg and Al- 2.5%Mg-0.2%Sc alloys during severe c... more Evolution of microstructure and texture in Al-2.5%Mg and Al-
2.5%Mg-0.2%Sc alloys during severe cold rolling and subsequent annealing was studied using electron back scatter diffraction (EBSD). These alloys were first thermo-mechanically processed to sheets of average thickness (~1mm) with well recrystallized microstructures. These sheets were subsequently severely coldrolled up to an equivalent strain of 4.32 using a combination of Accumulative Roll Bonding and conventional cold-rolling. The deformed alloys were subjected to isochronal annealing treatment for one hour in a wide temperature range. Development of Ultrafine lamellar microstructure subdivided by high angle grain boundaries (HAGB) and pure metal or copper type texture was observed in both the alloys during deformation. Al-Mg-Sc consistently showed higher hardness as compared to the Al-Mg.
Al-Mg recrystallized around ~ 2500C but in Al-Mg-Sc the
recrystallization was greatly delayed up to 500°C and the
deformation texture components were retained during annealing. The differences in the recrystallization behavior of two materials were discussed with regard to the deformation microstructure and presence of fine precipitates.

Research paper thumbnail of Texture Evolution During Cross Rolling and Annealing of High-Purity Nickel

Evolution of texture during cross rolling and subsequent annealing was studied in high-purity nic... more Evolution of texture during cross rolling and subsequent annealing was studied in high-purity nickel. For this purpose nickel samples were subjected to multipass cross rolling up to 90 pct reduction in thickness followed by annealing at different temperatures ranging between 673 K and 1073 K (400 °C and 800 °C). Cross rolling was carried out by rotating the samples about the normal direction (ND) by 90 deg interchanging the rolling direction and transverse direction (TD) between each consecutive pass. The development of microstructure and texture was characterized using X-ray and electron backscattered diffraction (EBSD) techniques. The deformation texture was characterized by the presence of strong brass ({110}h112i) and ND-rotated brass ({011}h211313i)) orientations. Upon annealing at 673 K (400 °C), ND||[111] fiber could be observed in the microtexture which originated from the twin formation of the recrystallized TD-rotated cube ({027}h072i) grains. The fiber was weakened after annealing at 1073 K (800 °C) because of the decreased propensity for twin formation, and the microtexture was found to be weak and diffused. EBSD studies on early recrystallization stages indicated the absence of preferential nucleation of cube grains being in agreement with a weak cube texture formation in annealed cross-rolled high-purity nickel.

Research paper thumbnail of Effect of Change in Strain Path During Cold Rolling on the Evolution of Microstructure and Texture in Al and Al-2.5%Mg

The effect of change in strain path during cold rolling on the evolution of microstructure and te... more The effect of change in strain path during cold rolling on the evolution of microstructure and texture is investigated. For this purpose, high purity aluminum and Al-2.5%Mg alloy are deformed ($90% reduction in thickness) by unidirectional and cross cold rolling. Irrespective of the alloy system, copper-type texture is observed in unidirectional processed materials, while strong brass ({011}AE112ae) texture is developed during cross rolling. Unidirectionally rolled aluminum showed higher HAGB fraction, but similar HAGB spacing as compared to the cross-rolled aluminum after 90% reduction in thickness. At the same time, the internal misorientation in the cross-rolled 2N-Al is higher than in the unidirectionally rolled material. In contrast, Al-2.5% Mg alloy processed differently in both ways shows similar HAGB fraction, spacing, and internal misorientation distribution. These observations indicate that microstructure evolution due to strain path change is more strongly affected by dynamic recovery as compared to texture evolution.

Research paper thumbnail of Microstructure and texture evolution during annealing of equiatomic CoCrFeMnNi high-entropy alloy

Evolution of microstructure and texture after heavy cold rolling and subsequent annealing in a wi... more Evolution of microstructure and texture after heavy cold rolling and subsequent annealing in a wide temperature range was first studied in an FCC equiatomic CoCrFeMnNi high-entropy alloy (HEA). Development of a submicron-cell structure and a strong brass-type texture was observed after 90% cold rolling. An ultra-fine microstructure having average recrystallized grain size $1 lm with profuse annealing twins was observed after annealing at 650 °C. Remarkable resistance against grain coarsening was observed at least up to 800 °C. The mechanisms for these features were closely related with the distinct whole-solute matrix in HEAs. The recrystallization texture was characterized by the retention of deformation texture components similar to those of TWIP and 316 stainless steels. But notable differences exist. The S ({1 2 3}h6 3 4i) component is stronger than brass ({1 1 0}h1 1 2i) and Goss ({1 1 0}h0 0 1i), and strengthened with increasing annealing temperatures. Strong a-fiber (h1 1 0i//ND) components other than the deformation components B S and G, and higher fraction of random components also develop. It could be attributed to profuse annealing twin formation due to the low stacking fault energy of the alloy.

Research paper thumbnail of Nucleation behavior and formation of recrystallization texture in pre-recovery treated heavily cold and warm-rolled Al–2.5 wt.%Mg alloy

Evolution of cube texture after annealing was investigated in severely cold and warm-rolled Al–2.... more Evolution of cube texture after annealing was investigated in severely cold and warm-rolled Al–2.5 wt.%Mg alloy without and with prior recovery treatments. The alloy was cold and warm-rolled at room temperature and at 473 K (200 °C), respectively, to 97% reduction in thickness and annealed at different temperatures ranging from 548 K (275 °C) to 673 K (400 °C). The warm-rolled material showed much stronger and sharper cube texture as compared to the cold-rolled material after different annealing treatments. However, prior recovery treatments at 473 K (200 °C) significantly diminished the strength of the cube texture in the warm-rolled material after annealing. In contrast, the strength of the cube component after annealing in the cold-rolled material was not significantly affected by the prior recovery treatments. The observed differences could be adequately explained by the preferential recovery and nucleation behavior of cube grains in different treated conditions.

Research paper thumbnail of Effect of Prior Recovery Treatment on the Evolution of Cube Texture During Annealing of Severely Warm-Rolled Al-2.5 wt pctMg Alloy

The effect of prior recovery on the evolution of cube texture ({001}h100i) in severely warm-rolle... more The effect of prior recovery on the evolution of cube texture ({001}h100i) in severely warm-rolled and annealed Al-2.5 wt pctMg alloy was studied. The Al-2.5 wt pctMg alloy was warm rolled to 97 pct reduction in thickness at 473 K (200 °C). The warm-rolled sheets were isochronally annealed for 1 hour at temperatures ranging from 523 K to 673 K (250 °C to 400 °C) without and with prior recovery treatments. In case of prior recovery, the sheets were pre-treated at 473 K (200 °C) for different time intervals ranging from 3.6 9 10 3 seconds (1 hour) to 8.64 9 10 4 seconds (24 hours) before the annealing. The warm-rolled alloy showed finely subdivided lamellar structure and strong presence of pure metal type texture. The annealed materials without any prior recovery treatment showed strong cube texture after annealing which could be attributed to the oriented nucleation of cube grains resulting from the preferentially recovered structure of cube regions in the warm-rolled state. In contrast, the cube texture was significantly weakened in materials subjected to different prior recovery treatments. The prior recovery treatments resulted in homogenous recovery which was confirmed by microstructural, textural, and conductivity measurements. Homogenous recovery eliminated the nucleation advantage of cube regions originating from the preferentially recovered structure and weakened the cube texture significantly. The present results indicated that prior recovery treatment could be effectively used to control recrystallization cube texture in severely warm-rolled aluminum alloys.

Research paper thumbnail of Microstructure and Texture of Al-2.5wt.%Mg Processed by Combining Accumulative Roll Bonding and Conventional Rolling

Evolution of microstructure and texture during severe deformation and annealing was studied in Al... more Evolution of microstructure and texture during severe deformation and annealing was studied in Al-2.5%Mg alloy processed by two different routes, namely, monotonic Accumulative Roll Bonding (ARB) and a hybrid route combining ARB and conventional rolling (CR). For this purpose Al-2.5%Mg sheets were subjected to 5 cycles of monotonic ARB (equivalent strain (e eq) = 4.0) processing while in the hybrid route (ARB + CR) 3 cycle ARB-processed sheets were further deformed by conventional rolling to 75% reduction in thickness (e eq = 4.0). Although formation of ultrafine structure was observed in the two processing routes, the monotonic ARB—processed material showed finer microstructure but weak texture as compared to the ARB + CR—processed material. After complete recrystallization, the ARB + CR-processed material showed weak cube texture ({001}AE100ae) but the cube component was almost negligible in the monotonic ARB-processed material-processed material. However, the ND-rotated cube components were stronger in the monotonic ARB-processed material-processed material. The observed differences in the microstructure and texture evolution during deformation and annealing could be explained by the characteristic differences of the two processing routes.

Research paper thumbnail of Annealing textures of severely cold and warm-rolled Al–2.5 wt.%Mg alloy

The evolution of recrystallization texture was investigated in severely deformed Al–2.5 wt.%Mg al... more The evolution of recrystallization texture was investigated in severely deformed Al–2.5 wt.%Mg alloy. For this purpose the alloy was cold and warm-rolled to 97% reduction in thickness at room temperature and 473 K (200 °C), respectively, using a combination of accumulative roll bonding and conventional rolling. The deformed materials were annealed at temperatures ranging between 473 K (200 °C) and 673 K (400 °C). The deformed materials showed fine lamellar structure and strong copper type texture. However , the warm-rolled material showed much stronger cube texture ({1 0 0}h0 01i) after different anneal-ing treatments. Orientations of early recrystallized grains in partially recrystallized materials obtained after annealing for short duration revealed strong tendency for preferential nucleation of cube grains in warm-rolled as compared to the cold-rolled material. The observed preferential nucleation of cube oriented grains in warm-rolled material was attributed to more recovered structure of cube oriented grains. In contrast, strong pinning of dislocations by solute Mg atoms during cold-rolling at room temperature inhibited the recovery of cube grains and greatly diminished their preferential nucleation. The cube component was significantly strengthened with increasing annealing temperature in both cold and warm-rolled materials due to the growth of the cube grains.

Research paper thumbnail of Microstructure, Texture and Hardness Properties of Bulk Ultrafinegrained Al-2.5%Mg and Al-2.5%Mg-0.2%Sc Alloys Processed by Accumulative Roll Bonding (ARB

Evolution of microstructure, texture and hardness properties during severe plastic deformation by... more Evolution of microstructure, texture and hardness properties during severe plastic deformation by accumulative roll bonding (ARB) was studied in Al-2.5%Mg and Al-2.5%Mg-0.2%Sc alloys using electron back scatter diffraction (EBSD) and micro hardness tester. Sheets of these alloys having 1 mm thickness were processed up to 7 cycles of ARB at room temperature corresponding to an accumulated equivalent strain (ɛ eq) of 5.6. Ultrafine lamellar microstructure with interlamellar spacing less than 400nm finely subdivided by high angle boundaries (misorientation angle >15°) was observed in both the alloys. Development of a strong β–fiber rolling texture could be observed in both alloys from the EBSD measurements. The hardness was found to increase monotonically with increasing number of ARB cycles in both materials. The key effect of Sc alloying was revealed by consistently higher hardness in Al-Mg-Sc as compared to the Al-Mg at all deformation levels. The increase in hardness in Al-Mg-Sc could be attributed to the presence of very fine Al 3 Sc precipitates in the starting material.