Electron Backscatter Diffraction (EBSD) is a scanning electron microscope (SEM) based technique, which enables Sample Microstructure to be analysed, visualised and quantified.
What is Sample Microstructure and why is it important?
Microstructure is the internal structure of a material investigated on the microscopic scale. It is of interest because a materials internal features (or structure) will influence its properties and behaviour. The term ‘Microstructure’ includes the identification and characterisation of grain populations, investigating the different phases or compounds in the material, often secondary phases, coupled with the spatial distribution of elements and analysing the interfaces between grains or within grains.
Characterising microstructure is fundamental in understanding a material and its performance. Material processing will govern the creation of the microstructure, which in turn influences the properties of the material. Therefore microstructure is increasingly important in a large range of industries and research areas, for example: metals research and processing, including speciality metals and engineered materials, renewable energy and solar cell development, developments in microelectronics and geological research.
EBSD is a well established accessory for the SEM, which is used for characterising microstructure. As a result, EBSD is being applied in numerous different application areas to assist in materials understanding, shown in the table below.
The data collected with EBSD is spatially distributed and is visualised in maps and images, and is powerful for looking at localised features or non homogeneous samples. It can be used to study specific grains, local texture changes and low volume phases. EBSD can provide good phase discrimination, and when used in conjunction with EDS (i.e. when the chemistry is also available) offers excellent phase identification. There are a number of benefits to using EBSD for microstructural characterisation, including:
- Spatial information, which can be visualised in maps and images, with spatial resolution of 10’s of nm
- Visualisation of microstructure for grain size and grain / subgrain and phase distribution
- Visualisation of local texture and local crystal misorientations from mm to 20nm
- Global crystallographic texture determination
- Local strain determinations
- Accurate identification of minor phases
|Industries||Materials||Typical EBSD Measurements|
|Metals research and processing||Metals, Alloys||Grain size|
|Aerospace||Intermetallics||Grain boundary characterisation|
|Automotive||Inclusions / precipitates / 2nd phases||Global texture|
|Microelectronics||Thin Films||CSL boundary characterisation|
|Earth Science||Solar Cells||Recrystallised / deformed fractions|
|Superconductors||Phase fractions / distributions|
|Metal / ceramic composites||Fracture analysis|
|Bone, teeth||Orientation & misorientation relationships between grains / phases|
Table 1. A summary of the different application areas and the typical types of measurement made using EBSD.
EBSD, how does it work?
Electron Backscatter Diffraction (EBSD) is a scanning electron microscope (SEM) based technique that gives crystallographic information about the microstructure of a sample. In EBSD, a stationary electron beam interacts with a tilted crystalline sample and the diffracted electrons form a pattern that can be detected with a fluorescent screen. The diffraction pattern is characteristic of the crystal structure and orientation in the sample region where it was generated. Hence the diffraction pattern can be used to determine the crystal orientation, discriminate between crystallographically different phases, characterise grain boundaries, and provide information about the local crystalline perfection.
When the electron beam is scanned in a grid across a polycrystalline sample and the crystal orientation is measured at each point, the resulting map reveals the grain morphology, orientations and boundaries. This data can also be used to show the preferred crystal orientation (i.e. texture) within the sample. Thus a complete and quantitative representation of the microstructure can be established with EBSD.
This website describes how an EBSD system works, and gives examples of the type of results EBSD can generate.