EBSD and TEM Characterization of Ultrafine Grained High Purity Aluminum Produced by Accumulative Roll-Bonding

2006 ◽  
Vol 512 ◽  
pp. 91-96 ◽  
Author(s):  
Naoya Kamikawa ◽  
X. Huang ◽  
Nobuhiro Tsuji ◽  
Niels Hansen ◽  
Yoritoshi Minamino
Keyword(s):  
Misorientation Angle ◽  
High Purity ◽  
Accumulative Roll Bonding ◽  
Structural Parameters ◽  
Rolling Direction ◽  
Structural Features ◽  
High Angle ◽  
Roll Bonding ◽  
High Purity Aluminum

High purity aluminum (99.99% purity) was severely deformed by accumulative roll-bonding (ARB) to a thickness reduction of 98.4%. Quantitative microstructural characterization of the deformed sample was carried out by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD scans at various locations from the sample surface to the mid-thickness revealed a fairly uniform and equiaxed structure, although a small fraction of an elongated structure parallel to rolling direction (RD) was also observed. Misorientation angle distributions for grain boundaries of which misorientation angle was larger than 2° were evaluated by EBSD, showing that more than 70% of the boundaries were high-angle ones (>15°). More detailed structural features, such as low-angle boundaries (<2°) and dislocations between boundaries were characterized by TEM. The TEM results indicated that about 17% of the boundaries have misorientations <2° and that the fraction of high-angle boundaries is about 52%. An estimated yield strength based on the structural parameters determined by TEM was in good agreement with the measured value.

Crystallography of the Low Angle Lamellar Band Boundaries in ARB- Processed Aluminum Sheet

2011 ◽  
Vol 702-703 ◽  
pp. 161-164
Author(s):  
M. Zakaria Quadir ◽  
Michael Ferry ◽  
P. R. Munroe
Keyword(s):  
Accumulative Roll Bonding ◽  
Structural Features ◽  
Aluminum Sheet ◽  
Extensive Investigation ◽  
Sheet Metals ◽  
High Angle ◽  
Structural Refinement ◽  
Roll Bonding ◽  
Dense Distribution ◽  
Crystallographic Orientations

Lamellar bands are the primary structural features in accumulative roll bonding (ARB) of sheet metals. The structural refinement in ARB sheets occur by forming a dense distribution of lamellar band boundaries. The lamellar band boundaries initiate as low angle interfaces, parallel to the existing lamellar band boundaries, irrespective of the crystallographic orientations of the parent lamellar bands. From an extensive investigation it was found that the transverse directions across the lamellar band boundaries are rotated by an angle equal to their misorientations. Such a phenomenon is not sustained when the boundaries turn to high angle.

Microstructure of Pure Ni Subjected to High Pressure Torsion

2010 ◽  
Vol 667-669 ◽  
pp. 529-534 ◽  
Author(s):  
Hong Wen Zhang ◽  
Xiao Xu Huang ◽  
Niels Hansen ◽  
Reinhard Pippan
Keyword(s):  
High Pressure ◽  
Misorientation Angle ◽  
High Pressure Torsion ◽  
Structural Parameters ◽  
Structural Features ◽  
Structural Refinement ◽  
Boundary Misorientation ◽  
Transmission Electron ◽  
Structure Strength

Plastic deformation leads to a structural refinement by introducing low angle dislocation boundaries and high angle boundaries in the initial coarse grains. To understand the mechanisms for the structural refinement and to establish the structure-strength relationship requires a precise characterization of key structural parameters, namely the boundary spacing and boundary misorientation angle. This study gives the results of such a characterization of pure Ni subjected to high pressure torsion (HPT) up to a strain of 300. The structural analysis was carried out by transmission electron microscopy in the longitudinal sample section in which the detailed structural features can be resolved. It is found that the microstructure in the HPT Ni samples is dominated by a lamellar structure. The spacing of the lamellar boundaries decreases and their misorientation angle increases with strain following a power law up to strain of 12, above which saturation is reached at a strain of about 34. The distribution of lamellar spacings normalized by their respective average values at each strain show an identical form. This scaling behavior is discussed also with reference to other metals and processing routes.

Lamellar Subdivision during Accumulative Roll Bonding of a Titanium Interstitial Free Steel

2005 ◽  
Vol 495-497 ◽  
pp. 351-356 ◽  
Author(s):  
Ana Carmen C. Reis ◽  
Leo Kestens ◽  
Yvan Houbaert
Keyword(s):  
Shear Strain ◽  
Accumulative Roll Bonding ◽  
Rolling Direction ◽  
Orientation Imaging Microscopy ◽  
Lamellar Microstructure ◽  
Composite Sample ◽  
Interstitial Free ◽  
High Angle ◽  
Roll Bonding ◽  
Interstitial Free Steel

Titanium alloyed interstitial free steel was processed by means of accumulative roll bonding (ARB) in order to obtain an ultrafine grained structure. Ten consecutive rolling passes were applied at 480°C with a nominal reduction of 50% per pass and an intermediate annealing treatment of 5 min. at 500°C. A total true strain was obtained of evM = 8.0 which corresponds to an accumulated reduction of 99.9%. Orientation imaging microscopy was used to evaluate textures and microstructures. A pronounced lamellar structure was observed until the 5th pass with an incidence of high angle grain boundaries predominantly parallel to the rolling direction. After the 6th pass (evM = 4.8) an increased fragmentation perpendicular to the rolling direction starts to develop in spite of the lamellar microstructure with an average spacing of approximately 1 µm. From the 7th pass onwards (evM ≥ 5.6) a random high angle grain boundary distribution develops which results in a more equi-axed ultrafine microstructure after the 9th pass (evM = 7.2) with an average grain width of 200 nm. As the rolling is carried out without lubrication, the surface areas display a slightly more fragmented structure than the midlayer sections and typical shear texture components are present in these surface zones (<110>//ND and <211>//ND fibre). Although the sheets are stacked upon each other after each subsequent pass, the shear strain microstructural and textural features are rapidly decomposed in the midlayer in each subsequent rolling pass which is clearly revealed by the cross sectional orientation scan on the composite sample. Hence it cannot be concluded that the surface shear strain significantly contributes to the grain fragmentation in the bulk volume of the composite sample.

Microstructure and Texture Evolution in Nickel during Accumulative Roll Bonding

2016 ◽  
Vol 879 ◽  
pp. 454-458 ◽  
Author(s):  
Jia Qi Duan ◽  
Md Zakaria Quadir ◽  
Michael Ferry
Keyword(s):  
Grain Boundaries ◽  
Accumulative Roll Bonding ◽  
Texture Evolution ◽  
Shear Bands ◽  
Rolling Direction ◽  
Sample Surface ◽  
Deformation Texture ◽  
Roll Bonding ◽  
Equiaxed Grains ◽  
Electron Back Scattered Diffraction

Microstructure and texture evolution of commercially pure Ni processed by accumulative roll-bonding (ARB) up to eight cycles were studied using electron back scattered diffraction (EBSD). During ARB processing, the original coarse equiaxed grains were gradually transformed into refined lamellar grains along the rolling direction (RD). Shear bands started forming after three cycles. The fraction of low angle grain boundaries (LAGBs) increased after the first and second cycle because of orientation spreading within the original grains. However, their fraction decreased with the evolution of high angle grain boundaries (HAGBs) during subsequent deformations, until saturation was reached after six cycles. Overall, the typical deformation texture components (S, Copper and Brass) were enhanced up to six ARB cycles and then only Copper was further strengthened. At higher cycles a higher Copper concentration was found near sample surface than the interiors due to a high frictional shear of ARB processing.

Ultra Grain Refinement of Low C Steels by Accumulative Roll Bonding

2006 ◽  
Vol 503-504 ◽  
pp. 311-316 ◽  
Author(s):  
I. Salvatori
Keyword(s):  
Accumulative Roll Bonding ◽  
Orientation Imaging Microscopy ◽  
Low Carbon Steel ◽  
Small Samples ◽  
Low Carbon ◽  
High Angle ◽  
Misorientation Distribution ◽  
Roll Bonding ◽  
Orientation Imaging ◽  
Annealing Conditions

Refinement of grain size is one of the biggest challenges to produce steels with improved combination of strength and toughness. Ultrafine structures are being produced world-wide on various materials, including low carbon steel, using different types of processes. However, the majority of these processes also exhibit severe limitations because they are generally restricted to small samples and are difficult to be implemented on an industrial scale. A promising technique for industrial implementation is the Accumulative Roll Bonding (ARB), a process able to supply large samples, even in the laboratory scale. In this paper, warm intense straining (ε = 4) by ARB was applied to a plain low-C steel in order to develop ultrafine grains, aiming at sizes around 1-2 μm, suitable to maintain an adequate combination of strength and ductility. The effect of annealing conditions on the evolution of the work-hardened microstructure and the bonding behaviour after each pass were investigated. Orientation Imaging Microscopy was used to investigate the microstructure and give a quantitative assessment of high angle and low angle boundaries. It is showed that the frequency of high angle grain boundaries increases with the strain but the misorientation distribution remained far from that typical of a recrystallised material.

Martensitic Transformation from Ultrafine Grained Austenite Fabricated by ARB in Fe-24Ni-0.3C

2010 ◽  
Vol 667-669 ◽  
pp. 361-366 ◽  
Author(s):  
Hamidreza Jafarian ◽  
Ehsan Borhani ◽  
Akinobu Shibata ◽  
Daisuke Terada ◽  
Nobuhiro Tsuji
Keyword(s):  
Martensitic Transformation ◽  
Accumulative Roll Bonding ◽  
Martensite Transformation ◽  
Early Stage ◽  
Crystallographic Analysis ◽  
High Angle ◽  
Metastable Austenite ◽  
Roll Bonding ◽  
Nucleation Sites ◽  
Ultrafine Grained

In this paper, martensitic transformation from ultrafine grained (UFG) austenite fabricated by accumulative roll bonding (ARB) process in a metastable austenite alloy was studied. Microstructural observations and crystallographic analysis were carried out by FE-SEM/EBSD. The results showed that elongated UFG austenite having 200-300 nm in thickness surrounded by high angle boundaries was obtained after 6 cycles of the ARB process. The martensite transformed from the UFG austenite showed characteristic morphology and texture. The martensite transformation starting (Ms) temperature increased after 1 cycle ARB, which is related to increasing amount of nucleation sites, such as low angle boundaries, introduced during early stage of ARB process. In contrast, by increasing the ARB cycles, Ms temperature decreased. Decreasing the Ms temperature could be correlated to strengthening of austenite by the ARB process.

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