Metallographic examination is an important part of the materials engineering process. It is used to study the properties, composition and structure of metals and alloys. To properly examine the material, the specimens must be cut accurately and safely to ensure that the results are accurate and reliable. This guide will discuss the best practices for cutting samples for metallographic examination.
Sectioning
The first and most important step in cutting samples for metallographic examination is to preserve the sample axes orientation. It is important to cut the sample in such a way that important sample directions, such as the Rolling Direction, Transverse Direction and Sample normal, are not lost. It is also important to avoid any damage or alteration to the sample that may occur during the cutting process, as this could lead to inaccurate results.
When examining failed parts, it is best to select a specimen that intersects the origin of the failure, if it can be identified on the surface. Depending on the type of failure, several specimens from the area of failure and adjacent areas may need to be taken.
Abrasive Cutting
Abrasive cutting (sectioning) is a popular method for cutting specimens for metallographic examination. This method offers the advantage of a smooth cut surface and a quick sectioning process. Low-speed cut-off wheels are typically used for cutting materials that would be damaged by heat generated by standard abrasive cutters. Coolant and proper speed control are essential for this process.
The selection of abrasive wheel is important to avoid introducing unnecessary levels of damage when cutting materials. A hard wheel is usually best for cutting soft stocks, whereas a soft wheel is preferred for cutting hard materials. A medium-hard silicon carbide abrasive wheel is a good general purpose cutoff wheel.
All abrasive-wheel sectioning should be done wet using water or water-soluble oil coolant to prevent excessive surface damage caused by overheating. Some laboratory cutoff machines provide for submerged wet cutting.
Abrasive Blade Selection Guidelines Chart
Diamond Wafer Blade Selection Guidelines
Sawing
Sawing is still a popular method for cutting specimens for metallographic examination. This method usually produces relatively little damage, as the surface damage is primarily mechanical deformation. Hardened steel saw blades are used to cut only materials softer than the saw blade. Oil or water-soluble oil should be used as a cutting fluid to avoid premature wear of the saw teeth and to minimize frictional heat.
Conclusion
Cutting samples for metallographic examination is an important part of the materials engineering process. This guide has discussed the best practices for cutting samples for metallographic examination, including abrasive cutting and sawing. It is important to remember to preserve the sample axes orientation, avoid any damage or alteration to the sample, and use the appropriate cutting fluid to ensure accurate and reliable results.