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A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains.
Dorte Juul Jensen is a senior scientist and head of the Center for Fundamental Research: Metal Structures in Four Dimensions and Materials Research Division, Risø DTU National Laboratory for Sustainable Energy, Roskilde, Denmark. Risø operates under the auspices of the Danish Ministry of Science, Technology and Innovation, researching a wide range of technologies and training Ph.D candidates in the sciences.
In physical chemistry and materials science, texture is the distribution of crystallographic orientations of a polycrystalline sample. A sample in which these orientations are fully random is said to have no distinct texture. If the crystallographic orientations are not random, but have some preferred orientation, then the sample has a weak, moderate or strong texture. The degree is dependent on the percentage of crystals having the preferred orientation.
Electron backscatter diffraction (EBSD) is a scanning electron microscopy (SEM) technique used to study the crystallographic structure of materials. EBSD is carried out in a scanning electron microscope equipped with an EBSD detector comprising at least a phosphorescent screen, a compact lens and a low-light camera. In the microscope an incident beam of electrons hits a tilted sample. As backscattered electrons leave the sample, they interact with the atoms and are both elastically diffracted and lose energy, leaving the sample at various scattering angles before reaching the phosphor screen forming Kikuchi patterns (EBSPs). The EBSD spatial resolution depends on many factors, including the nature of the material under study and the sample preparation. They can be indexed to provide information about the material's grain structure, grain orientation, and phase at the micro-scale. EBSD is used for impurities and defect studies, plastic deformation, and statistical analysis for average misorientation, grain size, and crystallographic texture. EBSD can also be combined with energy-dispersive X-ray spectroscopy (EDS), cathodoluminescence (CL), and wavelength-dispersive X-ray spectroscopy (WDS) for advanced phase identification and materials discovery.
In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new phases from the solid. They are also important to many of the mechanisms of creep. On the other hand, grain boundaries disrupt the motion of dislocations through a material, so reducing crystallite size is a common way to improve mechanical strength, as described by the Hall–Petch relationship.
A pole figure is a graphical representation of the orientation of objects in space. For example, pole figures in the form of stereographic projections are used to represent the orientation distribution of crystallographic lattice planes in crystallography and texture analysis in materials science.
Selected area (electron) diffraction is a crystallographic experimental technique typically performed using a transmission electron microscope (TEM). It is a specific case of electron diffraction used primarily in material science and solid state physics as one of the most common experimental techniques. Especially with appropriate analytical software, SAD patterns (SADP) can be used to determine crystal orientation, measure lattice constants or examine its defects.
In materials science, slip is the large displacement of one part of a crystal relative to another part along crystallographic planes and directions. Slip occurs by the passage of dislocations on close/packed planes, which are planes containing the greatest number of atoms per area and in close-packed directions. Close-packed planes are known as slip or glide planes. A slip system describes the set of symmetrically identical slip planes and associated family of slip directions for which dislocation motion can easily occur and lead to plastic deformation. The magnitude and direction of slip are represented by the Burgers vector, b.
In metallurgy, materials science and structural geology, subgrain rotation recrystallization is recognized as an important mechanism for dynamic recrystallisation. It involves the rotation of initially low-angle sub-grain boundaries until the mismatch between the crystal lattices across the boundary is sufficient for them to be regarded as grain boundaries. This mechanism has been recognized in many minerals and in metals.
Kikuchi lines are patterns of electrons formed by scattering. They pair up to form bands in electron diffraction from single crystal specimens, there to serve as "roads in orientation-space" for microscopists uncertain of what they are looking at. In transmission electron microscopes, they are easily seen in diffraction from regions of the specimen thick enough for multiple scattering. Unlike diffraction spots, which blink on and off as one tilts the crystal, Kikuchi bands mark orientation space with well-defined intersections as well as paths connecting one intersection to the next.
Engineering diffraction refers to a sub-field of neutron scattering which investigates microstructural features that influence the mechanical properties of materials. These include:
- lattice strain, a measure of distortion in crystals
- texture, a measure of grain orientations
- dislocation density, a measure of the microstructure
- grain morphology
In materials science, misorientation is the difference in crystallographic orientation between two crystallites in a polycrystalline material.
Three-dimensional X-ray diffraction (3DXRD) is a microscopy technique using hard X-rays to investigate the internal structure of polycrystalline materials in three dimensions. For a given sample, 3DXRD returns the shape, juxtaposition, and orientation of the crystallites ("grains") it is made of. 3DXRD allows investigating micrometer- to millimetre-sized samples with resolution ranging from hundreds of nanometers to micrometers. Other techniques employing X-rays to investigate the internal structure of polycrystalline materials include X-ray diffraction contrast tomography (DCT) and high energy X-ray diffraction (HEDM).
Thomas Benjamin Britton is a materials scientist and engineer based at The University of British Columbia. He is a specialist in micromechanics, electron microscopy and crystal plasticity. In 2014 he was awarded the Silver Medal of the Institute of Materials, Minerals and Mining (IOM3), a society of which he then became a Fellow in 2016.
Carol Trager-Cowan is a Scottish physicist who is a Reader in physics and Science Communicator at the University of Strathclyde. She works on scanning electron microscopy, including Electron backscatter diffraction (EBSD), diffraction contrast and cathodoluminescence imaging.
Electron channelling contrast imaging (ECCI) is a scanning electron microscope (SEM) diffraction technique used in the study of defects in materials. These can be dislocations or stacking faults that are close to the surface of the sample, low angle grain boundaries or atomic steps. Unlike the use of transmission electron microscopy (TEM) for the investigation of dislocations, the ECCI approach has been called a rapid and non-destructive characterisation technique
Angus J Wilkinson is a professor of materials science based at University of Oxford. He is a specialist in micromechanics, electron microscopy and crystal plasticity. He assists in overseeing the MicroMechanics group while focusing on the fundamentals of material deformation. He developed the HR-EBSD method for mapping stress and dislocation density at high spatial resolution used at the micron scale in mechanical testing and micro-cantilevers to extract data on mechanical properties that are relevant to materials engineering.
David Dye is a Professor of Metallurgy at Imperial College London. Professor Dye specialises in fatigue and micromechanics of aerospace and nuclear materials, mainly Ni/Co superalloys, Titanium, TWIP steel, and Zirconium alloys.
Transmission Kikuchi Diffraction (TKD), also sometimes called transmission-electron backscatter diffraction (t-EBSD), is a method for orientation mapping at the nanoscale. It’s used for analysing the microstructures of thin transmission electron microscopy (TEM) specimens in the scanning electron microscope (SEM). This technique has been widely utilised in the characterization of nano-crystalline materials, including oxides, superconductors, and metallic alloys.
Dark-field X-ray microscopy is an imaging technique used for multiscale structural characterisation. It is capable of mapping deeply embedded structural elements with nm-resolution using synchrotron X-ray diffraction-based imaging. The technique works by using scattered X-rays to create a high degree of contrast, and by measuring the intensity and spatial distribution of the diffracted beams, it is possible to obtain a three-dimensional map of the sample's structure, orientation, and local strain.
References
- ↑ Swansea University
- ↑ Randle, Valerie; Engler, Olaf (2000). Introduction to texture analysis : macrotexture, microtexture and orientation mapping (Digital printing 2003 ed.). Boca Raton: CRC Press. ISBN 978-9056992248.
- ↑ Randle, Valerie (1996). The role of the coincidence site lattice in grain boundary engineering. London: Institute of Materials. ISBN 9781861250063.
- ↑ "Awards archive | IOM3". www.iom3.org. Retrieved 28 September 2017.
- ↑ Shellie Nazarenus, Noted Scientist Shares Expertise, Calit2, University of California Irvine, November 13, 2008
- ↑ "Power sharing at the palace".
- ↑ "Science: 'Who's who'?". 4 December 2007.
- ↑ "Scopus preview - Scopus - Author details (Rändle, Valerie)". www.scopus.com. Retrieved 28 September 2017.
- ↑ "PEOPLE - What next for woman of the year?". The Engineer. 15 January 2000. Retrieved 27 September 2017.
- ↑ "About — Valerie Norris — Author". Valerie Norris. Retrieved 22 November 2023.
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