scholarly journals The Effects of Strain Annealing on Grain Boundary Distribution and Hardening in Superpure Nickel

1996 ◽  
Vol 28 (1-2) ◽  
pp. 71-79 ◽  
Author(s):  
C. B. Thomson ◽  
V. Randle
Keyword(s):  
Grain Boundary ◽  
Electron Backscatter Diffraction ◽  
Pure Nickel ◽  
Special Boundary ◽  
Special Boundaries ◽  
Commercially Pure ◽  
Electron Backscatter ◽  
Twin Formation ◽  
High Level ◽  
Backscatter Diffraction

Electron backscatter diffraction is applied to the study of texture and mesotexture in superpure nickel. Low level strain annealing is shown to influence the grain boundary population such that greater proportions of special boundaries exist. It is found that variations in the texture of a specimen are not reflected by characteristic changes in the grain boundary population, indicating that texture analysis cannot be applied to the prediction of special boundary densities. Mechanisms active during the evolution of special boundaries are discussed and compared to those involved under similar conditions in commercially pure nickel. It is shown that alnnealing twin formation need not be prevalent for a high level of special boundaries to form. Differences in the hardness of various boundary types are identified, such that low angle boundaries and ∑3 boundaries close to exact misorientation can be categorized separately to other boundaries, in that they show minimal hardening.

Towards Optimization of Grain-Boundary Structures in Annealed Nickel

1996 ◽  
Vol 54 ◽  
pp. 356-357
Author(s):  
C.B. Thomson ◽  
V. Randle
Keyword(s):  
Grain Boundary ◽  
Electron Backscatter Diffraction ◽  
Coincidence Site Lattice ◽  
Annealing Twin ◽  
Average Deviation ◽  
Special Boundaries ◽  
Boundary Rotation ◽  
Twin Formation ◽  
Backscatter Diffraction ◽  
Statistical Preference

Many properties of materials are influenced by intergranular structure. Increasing the number of grain boundaries with favourable properties, or ‘special’, boundaries, can enhance the performance of a material in service. However, the criteria that must be satisfied for a boundary to be classified as special are not widely understood. For example, it has been shown that Σ3 coincidence site lattice (CSL) boundaries alone present a resistance to corrosion greater than for other boundary types in nickel (fee). In contrast, Rolim Lopes et al. observed no statistical preference for Σ3s in the grain boundary network of FeAl (bcc), and Bouchet and Priester discovered that in nickel there was a weak propensity for segregation to several boundary types, including Σ3, Σ1 1 and Σl9a CSLs.Commercially pure and superpure nickel specimens have been subjected to the strain annealing treatments detailed in the Table. Fig. 1 shows the results from an electron backscatter diffraction study of the commercial purity specimens (CI to C4). It is clear that the only boundary types that increase in frequency with increased thermal processing are Σ3n (n=l,2,3) CSLs. An abundance of annealing twins was observed for sample C4, and is unique to this sample, and this accounts for the very high proportions of Σ3s. Samples CI to C3 were annealed under vacuum, whereas C4 was treated in air, and it is proposed that the dominant energy minimization mechanism has changed from grain/grain boundary rotation for samples CI to C3, to annealing twin formation for sample C4. If the structure of a grain boundary evolves towards the exact misorientation of what is considered a special CSL type, the special properties of that boundary will, in general, become more marked. Σ3s have been shown to possess special properties. Fig. 2 shows the average deviation from exact misorientation for the Σ3s in each sample, normalised by the Brandon criterion for maximum permitted deviation. This clearly indicates that the Σ3s created by annealing twin formation can be considered more special than those produced via grain/grain boundary rotations.

scholarly journals Coupling Automated Electron Backscatter Diffraction with Transmission Electron and Atomic Force Microscopies

2000 ◽  
Vol 6 (S2) ◽  
pp. 940-941
Author(s):  
A.J. Schwartz ◽  
M. Kumar ◽  
P.J. Bedrossian ◽  
W.E. King
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Thermomechanical Processing ◽  
Electron Backscatter Diffraction ◽  
Grain Boundary Character Distribution ◽  
Atomic Force ◽  
Transmission Electron ◽  
Electron Backscatter ◽  
Network Engineering ◽  
Backscatter Diffraction

Grain boundary network engineering is an emerging field that encompasses the concept that modifications to conventional thermomechanical processing can result in improved properties through the disruption of the random grain boundary network. Various researchers have reported a correlation between the grain boundary character distribution (defined as the fractions of “special” and “random” grain boundaries) and dramatic improvements in properties such as corrosion and stress corrosion cracking, creep, etc. While much early work in the field emphasized property improvements, the opportunity now exists to elucidate the underlying materials science of grain boundary network engineering. Recent investigations at LLNL have coupled automated electron backscatter diffraction (EBSD) with transmission electron microscopy (TEM)5 and atomic force microscopy (AFM) to elucidate these fundamental mechanisms.An example of the coupling of TEM and EBSD is given in Figures 1-3. The EBSD image in Figure 1 reveals “segmentation” of boundaries from special to random and random to special and low angle grain boundaries in some grains, but not others, resulting from the 15% compression of an Inconel 600 polycrystal.

Characterizing Slip Transfer In Commercially Pure Titanium Using High Resolution Electron Backscatter Diffraction (HR-EBSD) and Electron Channeling Contrast Imaging (ECCI)

2012 ◽  
Vol 18 (S2) ◽  
pp. 702-703 ◽  
Author(s):  
J.R. Seal ◽  
T. Bieler ◽  
M. Crimp ◽  
B. Britton ◽  
A. Wilkinson
Keyword(s):  
High Resolution ◽  
Electron Backscatter Diffraction ◽  
Pure Titanium ◽  
Commercially Pure Titanium ◽  
Contrast Imaging ◽  
Commercially Pure ◽  
Slip Transfer ◽  
Resolution Electron ◽  
Electron Backscatter ◽  
Backscatter Diffraction

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Application of Electron Backscatter Diffraction to Grain Boundaries

2010 ◽  
Vol 160 ◽  
pp. 39-46 ◽  
Author(s):  
Valerie Randle
Keyword(s):  
Grain Boundary ◽  
Electron Backscatter Diffraction ◽  
Experimental Methodology ◽  
Polycrystalline Materials ◽  
Grain Boundary Engineering ◽  
Network Characteristics ◽  
Grain Boundary Plane ◽  
Electron Backscatter ◽  
Measurement Strategies ◽  
Backscatter Diffraction

The technique of electron backscatter diffraction (EBSD) is ideal for the characterisation of grain boundary networks in polycrystalline materials. In recent years the experimental methodology has evolved to meet the needs of the research community. For example, the capabilities of EBSD have been instrumental in driving forward the topic of ‘grain boundary engineering’. In this paper the current capabilities of EBSD for grain boundary characterisation will be reviewed and illustrated by examples. Topics are measurement strategies based on misorientation statistics, determination of grain boundary plane distributions and grain boundary network characteristics.

scholarly journals Effects of Unidirection/Bidirection Torsional Thermomechanical Processes on Grain Boundary Characteristics and Plasticity of Pure Nickel

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 236
Author(s):  
Yao Lin ◽  
Shan Liu ◽  
Tao Wu ◽  
Guangchun Wang
Keyword(s):  
Grain Boundary ◽  
Electron Backscatter Diffraction ◽  
Pure Nickel ◽  
Random Boundary ◽  
Special Boundaries ◽  
Grain Boundary Characteristics ◽  
Thermomechanical Processes ◽  
Boundary Characteristics ◽  
Boundary Modification ◽  
Boundary Characteristic

The “torsion and annealing” grain boundary modification of pure nickel wires with different diameters was carried out in this paper. The effects of torsional cycles as well as unidirectional/bidirectional torsion methods on grain boundary characteristic distribution and plasticity were investigated. The fraction of special boundaries, grain boundary characteristic distributions and grain orientations of samples with different torsion parameters were detected by electron backscatter diffraction. Hardness measurement was conducted to characterize the plasticity. Then, the relationship between micro grain boundary characteristics and macro plasticity was explored. It was found that the special boundaries, especially Σ3 boundaries, are increased after torsion and annealing and effectively broke the random boundary network. The bidirectional torsion with small torsional circulation unit was the most conducive way to improve the fraction of special boundaries. The experiments also showed that there was a good linear correlation between the fraction of special boundaries and hardness. The plasticization mechanism was that plenty of grains with Σ3 boundaries, [001] orientations and small Taylor factor were generated in the thermomechanical processes. Meanwhile, the special boundaries broke the random boundary network. Therefore, the material was able to achieve greater plastic deformation. Moreover, the mechanism of torsion and annealing on the plasticity of pure nickel was illustrated, which provides theoretical guidance for the pre-plasticization of nickel workpieces.

Application of FIB-EBSD Tomography for Understanding Annealing Phenomena in a Cold Rolled Particle-Containing Nickel Alloy

2007 ◽  
Vol 558-559 ◽  
pp. 413-418 ◽  
Author(s):  
Wan Qiang Xu ◽  
Michael Ferry ◽  
Julie M. Cairney ◽  
John F. Humphreys
Keyword(s):  
Nickel Alloy ◽  
Focused Ion Beam ◽  
Electron Backscatter Diffraction ◽  
Ion Beam ◽  
Serial Sectioning ◽  
Dual Beam ◽  
Electron Backscatter ◽  
Cold Rolled ◽  
Twin Formation ◽  
Backscatter Diffraction

A typical dual-beam platform combines a focused ion beam (FIB) microscope with a field emission gun scanning electron microscope (FEGSEM). Using FIB-FEGSEM, it is possible to sequentially mill away > ~ 50 nm sections of a material by FIB and characterize, at high resolution, the crystallographic features of each new surface by electron backscatter diffraction (EBSD). The successive images can be combined to generate 3D crystallographic maps of the microstructure. A useful technique is described for FIB milling that allows the reliable reconstruction of 3D microstructures using EBSD. This serial sectioning technique was used to investigate the recrystallization behaviour of a particle-containing nickel alloy, which revealed a number of features of the recrystallizing grains that are not clearly evident in 2D EBSD micrographs such as clear evidence of particle stimulated nucleation (PSN) and twin formation and growth during PSN.

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