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Metallography is the study of a material’s microstructure: the arrangement of grains, phases, inclusions, and defects that exist at the microscopic level. These features play a critical role in determining the material’s properties, such as strength, hardness and corrosion resistance. Read this webpage to learn more about how and why metallography is an integral part of R&D, process control, and failure analysis.
The microstructure of a material is shaped by its composition and how it was processed, e.g., through casting, forging, heat treatment, or other manufacturing methods. To examine a material’s internal structure, metallography relies on techniques like light and electron microscopy, chosen based on the level of detail required.
While traditionally associated with metals, metallographic methods can be applied to virtually all material classes. In a broader context, the term materialography is used to reflect the wide scope of applications beyond metals – hence ceramography when working with ceramics. Whether you're analysing a high-strength alloy for aerospace, a polymer for medical devices, or a ceramic coating, metallography provides a window into the material’s internal world.
The microstructure of a material has a significant impact on its mechanical, thermal, and chemical properties. Characteristics such as grain size, phase distribution, porosity, and inclusions all influence how a material performs under real-world conditions. Metallography is used whenever there is a need to understand or verify these internal structures, making it an essential tool across many fields. Common applications include:
Whether in industry or academia, metallography helps link processing, structure, and performance, offering valuable insights for decision-making and innovation.
The goal of metallographic preparation is to reveal the true microstructure of a material. Only a well-prepared sample allows for a clear and accurate assessment of its internal features. During the preparation process, it is essential that the microstructure remains unaltered. Mechanical or thermal influences such as excessive force, heat, or improper handling can change the material’s structure and lead to misleading results. While the exact procedure may vary depending on the material, the general workflow follows a consistent sequence.
Cutting, or sectioning, is the first step in metallographic sample preparation. It involves removing a representative sample from the material for analysis. This is typically done using a cut-off machine, with the choice of machine and cut-off wheel depending on the material type, size, and hardness.
Whether the sample comes from a large casting or a fine wire: careful sectioning is critical. The goal is to isolate the area of interest without introducing thermal or mechanical damage. Excessive heat, vibration, or pressure during cutting can alter the microstructure near the cut surface resulting in inaccurate analysis. Different materials require specific cut-off wheels, e.g. wheels tailored for sectioning metals, ceramics, polymers, or composite materials.
After sectioning, samples are typically mounted in a polymer resin to protect the specimen during the subsequent preparation steps. Mounting is especially important for fragile geometries, thin coatings, or small parts, where mechanical damage can easily occur during grinding or polishing. Mounted specimens are also easier and safer to handle and standardizing the size of specimens allows for the efficient use of semi-automatic or fully automatic preparation systems.
There are two main mounting techniques:
Hot mounting: The specimen is placed in a mould with a thermosetting resin (e.g., phenolic or epoxy) and cured under heat and pressure. This method is typically used for robust materials that can tolerate elevated temperatures and pressures.
Cold mounting: The specimen is embedded in a liquid resin that cures at room temperature. This method is preferred for temperature-sensitive materials and porous samples. While no external heat is introduced into the system during cold mounting, temperatures exceeding 100 °C can be reached during curing.
The choice between hot and cold mounting depends on the material, the geometry of the sample, and the specific requirements of the application.
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For the microscopic assessment, a scratch- and damage-free surface is essential. This is achieved through a series of grinding and polishing steps, using increasingly fine abrasives to gradually remove material and eliminate surface deformation.
Grinding is the initial step, where coarser abrasives on rigid papers or discs are used to remove sectioning damage and create a flat, even surface. Polishing follows, using much finer abrasives to refine the surface and produce a mirror-like finish suitable for microscopy. Polishing is typically performed on cloth, with the abrasive added in the form of a suspension containing particles such as diamond or colloidal silica.
Grinding and polishing are usually carried out on manual or automated preparation systems, where the sample is pressed against a rotating surface. The choice of consumables (papers, cloths, and suspensions) depends on the material. For example, soft metals like aluminium require different consumables than brittle ceramics or hard steels.
In many cases, grinding and polishing alone are sufficient to prepare a sample for microscopic analysis. However, when the polished surface lacks sufficient contrast, the sample can be treated with an etchant to enhance visibility of microstructural features.
Etching involves applying a chemical or thermal treatment to the surface, which selectively attacks different grains, phases, or microstructural components. This controlled erosion enhances contrast, making features like grain boundaries, phase differences, or precipitates easier to distinguish under the microscope.
The choice of etchant depends on the material and the specific features being investigated. Etching must be performed carefully, as over-etching or under-etching can obscure important details or introduce artifacts.
Depending on the application and level of detail required, different microscopy techniques are used. However, before moving to microscopic methods, a macroscopic examination, using the unaided eye or low magnification (up to ~10×), can already provide useful information. It’s often used to inspect surface quality, welds, cracks or overall structural features and is a valuable first step in failure analysis and quality control.
Light Microscopy
This is the most common method in metallography. Using reflected light and magnifications up to ~1000×, optical microscopes reveal grain structures, phases, porosity, and defects. It's widely used for quality inspection and routine materials characterization.
Scanning Electron Microscopy (SEM)
SEM provides much higher magnification and depth of field. It’s ideal for analysing fine features, fracture surfaces, and composition (when combined with EDS). SEM can be used on unetched or etched samples and is a go-to method in research and failure analysis.
A more advanced technique used within SEM is EBSD (Electron Backscatter Diffraction), which maps the crystallographic orientations across the sample surface. It’s valuable for studying grain structure, phase identification, and material texture, but it requires extremely well-polished, deformation-free surfaces.
In addition to imaging techniques, hardness testing plays a crucial role in materialography, as it offers insight into a material’s strength and plastic deformation behaviour. It is often used alongside microstructural analysis for a more complete understanding of material properties.
Hardness testing involves applying a controlled force using a defined indenter, and then measuring the resulting indent left on the material’s surface. The size or depth of the indent is used to calculate a hardness value.
There are various standardized methods such as Vickers, Knoop, and Brinell, which differ in indenter geometry, applied load, and the way the indent is evaluated. For more detailed information about hardness testing, we recommend our webpages dedicated to this topic.
Metallography is more than just a lab procedure: it is a critical tool for understanding materials on a microscopic level. By carefully preparing samples through cutting, mounting, grinding, and polishing, and assessing the revealed microstructure using appropriate microscopy techniques, metallography provides essential insights into the structure and behaviour of metals, ceramics, polymers, and composites. For anyone working in materials science, metallography offers a way to connect what we see under the microscope with how materials perform in the real world.
Metallography is the study of the microscopic structure of materials. It typically involves preparing a specimen and then examining it under a microscope. By doing so, metallography reveals details like grain size, phases, and inclusions, which are critical for understanding a material’s properties and performance. Metallography is used for a variety of purposes in both industry and research. Common uses include quality control (to check that a material or component was processed correctly), failure analysis (to determine why a part broke or degraded), materials development (to design or improve materials by understanding the structure-property relationship), and verifying compliance with material specifications and standards.
Preparing a metallographic sample involves several key steps. First, a sample is cut from the larger piece to include the region of interest. This sample is then mounted in a stable medium (like a resin) to make it easier to handle. Next, the sample surface is ground and polished through a series of finer abrasives until it is extremely smooth and reflective. Often, the polished surface is then etched with a chemical solution to reveal the microstructural features. Once prepared, the sample can be examined under a microscope.
Metallography typically requires a range of specialized equipment. Key items include precision cut-off machines for sectioning of samples, mounting presses for embedding of specimens, and grinding/polishing machines with abrasive discs and polishing cloths to prepare the sample surface. Once the sample is prepared, microscopes are used for examination: optical microscopes for routine analysis and possibly an SEM (Scanning Electron Microscope) for higher magnification and in-depth analysis. Additionally, if mechanical properties are of interest, a hardness tester is used to measure hardness. On our webpage you can find the suitable machines and consumables for your specific needs.
