Practical accuracy of grain misorientation measurements by Kikuchi line technique

1995 ◽  
Vol 60 (2) ◽  
pp. 207-218 ◽  
Author(s):  
A Gemperle ◽  
J Gemperlová
Author(s):  
W. L. Bell

Disappearance voltages for second order reflections can be determined experimentally in a variety of ways. The more subjective methods, such as Kikuchi line disappearance and bend contour imaging, involve comparing a series of diffraction patterns or micrographs taken at intervals throughout the disappearance range and selecting that voltage which gives the strongest disappearance effect. The estimated accuracies of these methods are both to within 10 kV, or about 2-4%, of the true disappearance voltage, which is quite sufficient for using these voltages in further calculations. However, it is the necessity of determining this information by comparisons of exposed plates rather than while operating the microscope that detracts from the immediate usefulness of these methods if there is reason to perform experiments at an unknown disappearance voltage.The convergent beam technique for determining the disappearance voltage has been found to be a highly objective method when it is applicable, i.e. when reasonable crystal perfection exists and an area of uniform thickness can be found. The criterion for determining this voltage is that the central maximum disappear from the rocking curve for the second order spot.


Author(s):  
J. I. Bennetch

In a recent study of the superplastic forming (SPF) behavior of certain Al-Li-X alloys, the relative misorientation between adjacent (sub)grains proved to be an important parameter. It is well established that the most accurate way to determine misorientation across boundaries is by Kikuchi line analysis. However, the SPF study required the characterization of a large number of (sub)grains in each sample to be statistically meaningful, a very time-consuming task even for comparatively rapid Kikuchi analytical techniques.In order to circumvent this problem, an alternate, even more rapid in-situ Kikuchi technique was devised, eliminating the need for the developing of negatives and any subsequent measurements on photographic plates. All that is required is a double tilt low backlash goniometer capable of tilting ± 45° in one axis and ± 30° in the other axis. The procedure is as follows. While viewing the microscope screen, one merely tilts the specimen until a standard recognizable reference Kikuchi pattern is centered, making sure, at the same time, that the focused electron beam remains on the (sub)grain in question.


2007 ◽  
Vol 353-358 ◽  
pp. 1165-1168
Author(s):  
Yan Hai Xu ◽  
Hao Li ◽  
Li Guo

The influences of crystallographic and geometric parameters such as grain misorientation on the performance of short cracks are illustrated based on FEM in this paper. Firstly, the microstructure is simulated to account for the effects of grain misorientation on the performance of short cracks and the short cracks are initiated within the microstructure for the further investigation. The influence of grain misorientation is demonstrated by the change of neighboring grain orientations with an initiated short crack from 0° to 180°. The effects of the grain boundary on the short crack with the crack arrested or retarded are described by the crack propagation until it approached the grain boundary. The results will give more useful information such as crack arrested and retardation to the further research on the characteristics and evolution of short cracks.


2018 ◽  
Vol 49 (12) ◽  
pp. 6390-6400 ◽  
Author(s):  
Sensen Huang ◽  
Yingjie Ma ◽  
Shilin Zhang ◽  
Sabry S. Youssef ◽  
Jianke Qiu ◽  
...  

Author(s):  
K. Nakano ◽  
Y. Tanaka ◽  
H. Suzuki ◽  
K. Hayakawa ◽  
M. Kurodai

Abstract. Unmanned aerial vehicles (UAVs) equipped with image sensors, which have been widely used in various fields such as construction, agriculture, and disaster management, can obtain images at the millimeter to decimeter scale. Useful tools that produce realistic surface models using 3D reconstruction software based on computer vision technologies are generally used to produce datasets from acquired images using UAVs. However, it is difficult to obtain the feature points from surfaces with limited texture, such as new asphalt or concrete, or detect the ground in areas such as forests, which are commonly concealed by vegetation. A promising method to address such issues is the use of UAV-equipped laser scanners. Recently, low and high performance products that use direct georeferencing devices integrated with laser scanners have been available. Moreover, there have been numerous reports regarding the various applications of UAVs equipped with laser scanners; however, these reports only discuss UAVs as measuring devices. Therefore, to understand the functioning of UAVs equipped with laser scanners, we investigated the theoretical accuracy of the survey grade laser scanner unit from the viewpoint of photogrammetry. We evaluated the performance of the VUX-1HA laser scanner equipped on a Skymatix X-LS1 UAV at a construction site. We presented the theoretical values obtained using the observation equations and results of the accuracy aspects of the acquired data in terms of height.


2017 ◽  
Vol 23 (3) ◽  
pp. 215 ◽  
Author(s):  
Jan Marek Dutkiewicz ◽  
Stanislav Rusz ◽  
Dariusz Kuc ◽  
Ondrej Hilser ◽  
Paweł Pałka ◽  
...  

<p>Magnesium based alloy containing 9 wt. % Li, 1,5 wt. % Al, composed of a + b (hcp + bcc) phases was cast under argon atmosphere and extruded at 350<sup>o</sup>C. Up to 3 passes of Twist Channel Angular Pressing TCAP deformation was applied at 160<sup>o</sup>C. TCAP tool consisted of helical part in horizontal area of the channel with angle of lead γ = 30° to simulate back pressure. The initial grain size of hexagonal a phase estimated at 30 mm decreased in following passes down to 6 mm and that of bcc b phase decreased after TCAP from initial 12 mm down to 5 mm. TEM studies after TCAP passes showed higher dislocation density in the b region than in the a phase. Crystallographic relationship (001) a || (110) b indicated parallel positioning of slip planes of both phases. Electron diffraction confirmed increase of grain misorientation with number of TCAP passes. Stress/strain curves measured at temperature 200<sup>o</sup>C showed superplastic forming after 1<sup>st</sup> and 3<sup>rd</sup> TCAP pass. Values of strain rate sensitivity coefficient <em>m</em> were calculated at 0.31 after 1 TCAP pass and increased after 3<sup>rd</sup> TCAP pass up to 0.47 for the strain rate range 10<sup>-5</sup> – 5 10<sup>-4</sup>. Increase of number of TCAP passes had positive effect on superplastic properties due to finer grains and increase of their misorientation;</p>


2007 ◽  
Author(s):  
Yuriy Perlovich ◽  
Vladimir Fesenko ◽  
Margarita Isaenkova ◽  
Vladimir Goltcev

Author(s):  
Zili Zhang ◽  
Xing Huang ◽  
Chunyan Cui ◽  
Hao Wang ◽  
Feifei Niu ◽  
...  

Abstract This paper presents a novel Nb superconducting joint with an ultralow resistance of 7.9 × 10-16 Ω, fabricated using the electron beam welding (EBW) method. After the EBW process, the two Nb filaments formed a single joint with a much larger grain size and smaller grain misorientation. More importantly, the resistance of the EBW Nb joint was nearly one magnitude lower than that of most conventional pressing joint. The ultralow resistance is essential for superconducting gravimeters, which require an extremely low drift rate. The EBW Nb joint allowed the superconducting gravimeter to have a much better performance when applied in the field of structural geology, geodesy, microgravity, and metrology. We believe that the EBW method could be one of the most promising joint fabrication methods for achieving maximum stability (less than 1 μgal/yr).


1999 ◽  
Vol 5 (S2) ◽  
pp. 236-237 ◽  
Author(s):  
J. A. Sutliff

This work describes the investigation of plastic strain in tensile deformed polycrystalline copper using the automated Electron BackScatter Pattern (EBSP) technique of electron diffraction in the Scanning Electron Microscope (SEM). A strong correlation was found between the known accumulated plastic strain in OFHC copper tensile specimens and quantitative measurements of intra-grain misorientation obtained from an analysis of automated-EBSP data.Previous works on strain measurement using EBSP analysis have focused on the influence of dislocation density on the intensity profiles of diffraction bands. It is known that for some materials, like copper, deformation strain produces highly organized dislocation structures and thus the dislocation density is very inhomogeneous on the sub-micron scale probed by EBSP. This suggests that plastic strain analysis using the EBSP dislocation density analysis route will be difficult to reliably implement in these materials.


Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3761
Author(s):  
Xiang-Long Peng ◽  
Gan-Yun Huang ◽  
Swantje Bargmann

Interaction between dislocations and grain boundaries (GBs) in the forms of dislocation absorption, emission, and slip transmission at GBs significantly affects size-dependent plasticity in fine-grained polycrystals. Thus, it is vital to consider those GB mechanisms in continuum plasticity theories. In the present paper, a new GB model is proposed by considering slip transmission at GBs within the framework of gradient polycrystal plasticity. The GB model consists of the GB kinematic relations and governing equations for slip transmission, by which the influence of geometric factors including the misorientation between the incoming and outgoing slip systems and GB orientation, GB defects, and stress state at GBs are captured. The model is numerically implemented to study a benchmark problem of a bicrystal thin film under plane constrained shear. It is found that GB parameters, grain size, grain misorientation, and GB orientation significantly affect slip transmission and plastic behaviors in fine-grained polycrystals. Model prediction qualitatively agrees with experimental observations and results of discrete dislocation dynamics simulations.


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