Recent Developments of Crystallographic Analysis Methods in the Scanning Electron Microscope for Applications in Metallurgy

Abstract

The field of metallurgy has greatly benefited from the development of electron microscopy over the last two decades. Scanning electron microscopy (SEM) has become a powerful tool for the investigation of nano-and microstructures. This article reviews the complete set of tools for crystallographic analysis in the SEM, i.e., electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), and electron channeling contrast imaging (ECCI). We describe recent relevant developments in electron microscopy, and discuss the state-of-the-art of the techniques and their use for analyses in metallurgy. EBSD orientation measurements provide better angular resolution than spot diffraction in TEM but slightly lower than Kikuchi diffraction in TEM, however, its statistical significance is superior to TEM techniques. Although spatial resolution is slightly lower than in TEM/ STEM techniques, EBSD is often a preferred tool for quantitative phase characterization in bulk metals. Moreover, EBSD enables the measurement of lattice strain/rotation at the sub-micron scale, and dislocation density. TKD enables the transmitted electron diffraction analysis of thin-foil specimens. The small interaction volume between the sample and the electron beam enhances considerably the spatial resolution as compared to EBSD, allowing the characterization of ultra-finegrained metals in the SEM. ECCI is a useful technique to image near-surface lattice defects without the necessity to expose two free surfaces as in TEM. Its relevant contributions to metallography include deformation characterization of metals, including defect visualization, and dislocation density measurements. EBSD and ECCI are mature techniques, still undergoing a continuous expansion in research and industry. Upcoming technical developments in electron sources and optics, as well as detector instrumentation and software, will likely push the border of performance in terms of spatial resolution and acquisition speed. The potential of TKD, combined with EDS, to provide crystallographic, chemical, and morphologic characterizations of nano-structured metals will surely be a valuable asset in metallurgy.

crystalAligner: a computer program to align crystal directions in a scanning electron microscope by global optimization

“…This contrast is known as electron channelling contrast and is closely related to diffraction contrast in a transmission electron microscope (TEM) (Zaefferer & Elhami, 2014;Borrajo-Pelaez & Hedströ m, 2018). The contrast obtained from detecting backscattered electrons in a scanning electron microscope (SEM) is dominated by the atomic number of the atoms in the probed volume.…”

“…In addition to this contrast, the intensity of backscattered electrons originating from crystalline materials is affected by the lattice spacing and the orientation of the ISSN 1600-5767 # 2020 International Union of Crystallography crystal lattice with respect to the axis of the primary beam. This contrast is known as electron channelling contrast and is closely related to diffraction contrast in a transmission electron microscope (TEM) (Zaefferer & Elhami, 2014;Borrajo-Pelaez & Hedströ m, 2018).…”

Effect of Inoculation on Phase Formation and Indentation Hardness Behaviour of Zr<SUB>47.5</SUB>Cu<SUB>45.5</SUB>Al<SUB>5</SUB>Co<SUB>2</SUB> and Zr<SUB>65</SUB>Cu<SUB>15</SUB>Al<SUB>10</SUB>Ni<SUB>10</SUB> Bulk Metallic Glass Matrix Composites

“…Only three notable studies have been recently reported [40] [41] [42] but they are only qualitative and are limited by mere generalised phase identification. This is a new and unique technique which has been reported as complimentary to transmission electron microscopy [43] [44]. It has unique ability to identify [45] and map crystallinity in materials [46] [47] [48] [49].…”

“…With the help of energy dispersive X-ray spectroscopy (EDS) detector, it can also generate map of crystal structure of individual elements which can help identify their nature and microstructural features (e.g. primary, secondary and tertiary dendrite arm spacing) [43] [52]. It also generates pole figures and grain size histograms which again can be used to determine mechanical properties of material.…”

Microstructure evolution during tempering of martensitic Fe–C–Cr alloys at 700 °C

“…Compared to the quantification of the thickness using TEM, the main advantage of ECCI is its capability to capture a large amount of laths in a quicker way. It has proven to be a powerful tool when combined with EBSD to evaluate microstructural parameters like misorientation distribution [31]. EBSD analysis was specifically used here to evaluate the ''unit size'' and to perform correlative work with ECCI so as to identify precipitation at certain boundaries.…”