Understanding and evaluating materials
Evaluating structural properties and behaviour of materials at a micro level can help understand what may be happening at a larger scale when a material is exposed to defined conditions over its expected lifetime.
NPL offers a complete package of microstructural characterisation, testing and consultancy for materials including metals, ceramics, polymer composites, surfaces and coatings all the way to foods, pharmaceuticals, bones and tissue. There are various measurements available, such as assessing porosity, texture, deformation, surfaces, grainsize and particle size
Scanning electron microscopy (SEM)
Our high magnification SEMs and dual beam (FIB) SEM can visualise surfaces and structures in 2D and 3D to a nanoscopic scale. They are fitted with the latest detectors and state of the art stages for accurate positioning and repositioning of samples, supporting the understanding of the performance of materials used in harsh environments such as temperature, wear and corrosion, determining the root cause of failure, to characterise properties and to make better material selection and lifetime prediction. Our research is focussed on improving the accuracy of measurements derived from ion and plasma beam milling by accurately understanding slice thickness variation, the use of digital image correlation to measure residual stress and the micron scale and changes in structure caused by ion implantation. We are also developing the use of direct electron detectors for faster EBSD mapping
Electron back scattered diffraction (EBSD)
EBSD can provide accurate measurement of phase distribution, grain size and orientation in crystalline materials and identify the development of damage in the material. NPL are working to improve the accuracy, resolution and speed of these analyses to provide the most reliable service, supporting the understanding of the structure and failure mechanisms in materials.
In-situ mechanical testing
The large working chambers of the microscopes allow for other specialised test equipment to be inserted so that the results of crack growth, scratch or indentation/compression tests can be observed directly in minute detail.
Optical microscopy and 3D surface analysis
The optical microscopy and image analysis facility is equipped with a range of instruments to obtain high resolution colour digital images to a maximum microscope magnification of x2,500. The microscopes are fitted with the highest NA (numerical aperture) objectives to ensure the highest resolution of detail. Infinite focus microscopes can provide representation in 3D and allow measurements of cross-sections, volumes, areas and surface roughness, or fully focused images in 2D of 3D objects.
All the microscopy methods above rely on accurate analysis of the images produced. Understanding the uncertainties arising from limitations in resolution, segmentation or diffraction pattern analysis is an important area of work.
Metallographic preparation, cutting, polishing, etching
Our metallographic preparation facility underpins many of the materials testing programs at NPL. The facility supports research into a wide range of materials:
- Polymers and composites
- Metal matrix composites
- Hardmetals and cermets
- Electronic interconnects
- Surfaces for bio-tissue growth
- Surface preparation for reference materials
A full range of sectioning equipment is available, as well as a range of automatic and semi-automatic polishing machines to ensure rapid and repeatable preparation of either hot or cold mounted specimens up to 50 mm diameter.
We actively participate on standards committees and we are a corporate member of the Royal Microscopical Society. We also offer a consultancy for solving material characterisation problems.
Further information is available in our Good Practice Guides.
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Find out more about NPL’s research on Microstructural characterisation