What is Metallography?
Metallography is the scientific study of the microstructure of metallic materials. It is a tool for understanding the relationship between the microscopic structure and macroscopic properties, such as tensile strength or electrical properties. Using microscopy, it is possible to observe the constituents, grains, inclusions or phases in alloys, and to thereby determine their chemical and atomic structure and spatial distribution.
The Pioneering Work of Henry Clifton Sorby
Henry Clifton Sorby was a 19th century scientist who made great contributions to the field of metallography. He was the first to recognize the significance of the microstructure in understanding the macroscopic properties of metals, and his work in Sheffield (UK) with modern manufactured iron and steel was groundbreaking. Sorby’s pioneering work paved the way for the metallography that we know today.
Techniques Used in Metallography
Light microscopy is the most widely-used technique in metallography. Brightfield mode is the most common, but other contrasting techniques, such as darkfield or differential interference contrast (DIC), and the use of color etching, are also used. By using these techniques, it is possible to reveal the microstructural features of metals and gain insights into their macroscopic properties.
Metallography: An Introduction to Examining the Microstructure of Metals and Alloys
Metallography is the study of the constitution and microstructure of metals and alloys. Examining the material’s surface with optical microscopy can reveal much information, but more advanced techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are often necessary for research and advanced analysis. Preparing samples for metallographic examination is a process that requires skill and expertise, and incorrect techniques can lead to altering the true microstructure and erroneous conclusions.
Metallography – Unlocking the Secrets of Metal Structure and Behavior
Metallography is a complex branch of science that deals with the study of metal and alloy structure and properties. It is of utmost importance for a variety of industries and applications, from automotive to aerospace. This type of analysis is a key factor in determining the performance of a material and has been heavily studied and developed over the years.
In the past, metallography was limited by the resolution of the reflected light microscope used to study the specimens. Now, with the development of transmission and scanning electron microscopies (TEM and SEM) and X-ray diffraction methods, this limitation has been overcome. These advanced techniques allow for a much more detailed study of metals and alloys at the atomic level.
Using these powerful tools, metallographers can now analyse the structure and composition of metals and alloys, control their processing and study their influence on properties and behaviour. They can also use metrological and stereological methods and computer-aided image analysis to measure microstructural features.
Important Safety Considerations When Working with Metallography
Working with metallography requires special safety considerations, as many of the reagents used in the preparation of etchants are highly corrosive and/or extremely toxic. Additionally, some etchants can be hazardous even when diluted, and all etchants have a limited shelf life.
It is essential to understand the risks associated with the etchant being used and to ensure that the metallographer is adequately trained and equipped with the necessary safety equipment. It is also important to consider the safe and legal disposal of used or discarded etchants.
Metallography is a complex branch of science with significant implications for many industries and applications. With the development of transmission and scanning electron microscopies (TEM and SEM) and X-ray diffraction methods, it is now possible to study metals and alloys at the atomic level and to accurately determine their structure and composition. However, due to the hazardous nature of the reagents used in etching, it is essential to take all necessary safety precautions when working with metallography.
Preparation for metallography involves five major steps as below.
Sectioning
Sectioning is the first step in preparing a sample for metallographic examination. This is the process of cutting a sample into a manageable size, typically a few millimeters thick, which can be placed in the microscope. Samples can be cut with a abrasive cutoff saw, waterjet, or wire EDM machine.
Mounting (optional)
Mounting is an optional step in the metallography process. During this step, the sample is embedded in a thermoplastic or thermosetting resin. This provides more stability to the sample and makes it easier to machine.
Grinding
Grinding is the process of using abrasive materials to remove material from the sample. This is done in order to create a flat surface that can be examined under the microscope. This can be done with a variety of abrasive materials such as silicon carbide and diamond abrasive papers and cloths.
Polishing
Polishing is the next step in the metallography process. This is done in order to create a smooth, reflective surface on the sample so that it can be examined under the microscope. This is typically done with diamond suspensions, pastes, and creams.
Etching
Etching is the final step in preparing a sample for metallographic examination. This is the process of exposing the microstructure of the sample by using a chemical reagent. This can provide valuable information about the microstructure that cannot be seen under a microscope. Common reagents used in etching are nitric acid, hydrofluoric acid, and sodium hydroxide.