Delphic Chen

Effect of microscopic parameters on EBSD spatial resolution

In this study, a quantitative approach is proposed to understand the effect of the accelerating voltage and the probe current on the physical resolution of EBSD. The accelerating voltage was varied from 5 to 30kV and probe currents of 1, 10, and 40nA were selected. The lateral, longitudinal, and depth resolutions at 10kV and 1nA were 34.5, 44.7, and 46nm for copper, respectively. When the accelerating voltage was in the range of 5-20kV, the ratio of the longitudinal to the lateral resolution was below the theoretical ratio of 2.9. Considering the channeling effect, the best physical depth resolution of 38nm was achieved at 5kV and 10nA. The physical depth resolution in an EBSD measurement is much larger due to the channel effect than that obtained without considering this effect.

EBSD characterization of twinned copper using pulsed electrodeposition

We investigated the influence of pulse current density on a crystallographic microstructure of twin Cu films through x-ray diffraction and electron backscatter diffraction (EBSD). With an increase in the pulse current density, the intensity of the preferred orientation (texture), grain size and the fraction of the twins decreased. The high-density twin copper films, including the nanotwins observed from the orientation image maps, were achieved using a pulsed electrodeposition technique at the current density of 0.5 A cm−2, with an average grain size of 818 nm. The crystallographic microstructure of the high-density twin copper films shows a 0 1 1 preferred orientation associated with the 60°1 1 1 twin having a {1 1 1} twin plane.

Characterization of Laves phase in Crofer 22 H stainless steel.

This study investigated the effect of annealing temperature on the precipitation behavior of Crofer(®) 22 H at 600°C, 700°C, and 800°C. The grain size distribution, precipitate phase identification, and microstructure were analyzed using electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). The morphology of Laves phase (Fe,Cr,Si)(2)(Nb,W) precipitates having the Cr(2)Nb structure changed from strip-like to needle-shaped as the annealing temperature was increased. The precipitates of the Laves phase also shifted from the grain boundaries to the grain interiors when the temperature was increased. However, the average grain size (150 μm) of the ferritic matrix did not significantly change at 600°C, 700°C, and 800°C for 10 h.

Effect of Plating Current Density and Frequency on the Crystallographic Texture of Electrodeposited Copper

For interconnect materials in the microelectronic technology copper has replaced aluminum due to its lower resistivity, higher thermal conductivity and better electromigration resistance. Recently, it was found that nanotwinned copper exhibits ultra high yield strength, ductility and electrical conductivity. Therefore, in this study the effect of plating current density and frequency were investigated on the crystallographic texture of Cu electrodeposited to understand the twin character. Electron backscatter diffraction (EBSD) was used for characterizing the preferred orientation, grain size distribution, and grain boundary character distribution. Three kinds of <110>, <111> and <112> textures were found to be related with the electrodeposited parameters of current density and frequency. Here we will discuss the relationship between the preferred orientation and the electrodeposited parameters.

The effect of atomic mass on the physical spatial resolution in EBSD

In this study, bicrystals of silver (Ag) and aluminum (Al) were used to investigate the physical spatial resolution of the electron backscatter diffraction system combining a digital image correlation method. Furthermore, the effect of the accelerating voltage and probe current was investigated on the physical spatial resolution of the lateral and longitudinal resolutions for Ag and Al, respectively. The lateral and longitudinal resolutions show high dependency on the accelerating voltage for a low atomic mass material of Al, In addition, these are almost independent of the accelerating voltage for a high atomic mass material of Ag. Moreover, the probe current does not play any role on both the lateral and longitudinal resolutions. The best lateral resolutions for Al and Ag are 40.5 and 12.1 nm at 10 kV and 1 nA, respectively. The best longitudinal resolutions of 23.2 and 80 nm were obtained at 10 kV and 1 nA for Al and Ag, respectively.

EBSD and electron channeling study of anomalous slip in oligocrystals of high chromium ferritic stainless steel

In the present study, electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) techniques were applied to investigate the deformation pattern of coarse ferrite grains after being subjected to 3%, 6%, and 10% tensile deformation. Oligocrystals of Crofer® 22H ferritic steel were obtained as experimental material at 1075°C for 22min annealing. Using kernel average misorientation (KAM) mapping obtained from EBSD, possible slip planes are (110), (101), (12-1) and (32-1) in grain A; (0-11), (-101), (-112), (1-21) in grain B; and (0-11), (1-21) and (11-2) in grain C. Combining ECCI and EBSD techniques enables us to identify two a0[11¯1]/2 edge dislocations that occur on the (110)[1-11] and (32-1)[1-11] slip systems for grain A, thereby breaking down Schmids law.

Application of edge detection method based on image quality gradient for twin detection

An image quality based method was applied to quantitatively analyse the contribution of electrodeposited copper twinning. This method, based on the image quality as obtained from electron backscattering diffraction, involves three processes: hexagonal edge detection, thinning algorithm and twin determination. The twin density determined by the new algorithm was 65.61% which is higher than the twin density, 57.44% as determined by the Orientation Imaging Microscopy (OIM) analysis. The newly developed algorithm provides an alternative to twin boundary detection.

Effect of prior deformation on microstructural development and Laves phase precipitation in high-chromium stainless steel

This study investigated the influence of deformation on precipitation behaviour and microstructure change during annealing. Here, the prior deformation of high‐chromium stainless steel was tensile deformation of 3%, 6% and 10%, and the specimens were then annealed at 700˚C for 10 h. The specimens were subsequently analyzed using backscattered electron image and electron backscattering diffraction measurements with SEM. Compared with the deformation microstructure, the grains revealed no preferred orientation. The precipitates of TiN and NbC were formed homogenously in the grain interior and at grain boundaries after annealing. Fine Laves phase precipitates were observed in grains and along subgrain boundaries as the deformation increased. Furthermore, the volume fraction of Laves phase increased, but the average particle diameter of precipitate was reduced as the deformation increased.

Orientation contrast of secondary electron images from electropolished metals.

Orientation contrast obtained by an in-lens secondary electron detector in a scanning electron microscope from electropolished/etched metals is reported. The imaging conditions for obtaining such orientation contrast are defined. The mechanism responsible for the formation of the orientation contrast is explained, and an application example of this new imaging method is given.

Grain Boundary Evolution of Cold-Rolled FePd Alloy during Recrystallization at Disordering Temperature

In this study, the grain boundary character and texture of 50% and 90% cold-rolled FePd alloy was investigated during recrystallization at 700 °C. Electron backscatter diffraction (EBSD) measurements were performed on the rolling direction to normal direction section. Kernel average misorientation (KAM) calculated from EBSD measurements was employed to determine the recrystallization fraction. The Avrami exponent n of recrystallization is 1.9 and 4.9 for 50% and 90% cold rolling, respectively. The new formation of texture reveals random texture during the recrystallization process. As annealing time increased, the number of high angle boundary (HAGB) and coincidence site lattice (CSL) increased with consumption of low angle boundary (LAGB). In addition, possible transformations between different grain boundaries are observed here.