Similar to how any analysis works, the specimens for metallographic analysis also first undergoes sample preparation procedure. The proper preparation of metallographic specimens is a crucial step for the determination of accurate microstructure of a material.

There are almost six to seven steps involved in metallographic sample preparation. These are – sectioning, mounting, course grinding, fine grinding, etching and microscopic examination. The first step of sample preparation is Sectioning.

Continue to read till the end to learn about metallographic sample preparation and its first step – Sectioning.

Overview of Metallographic Sample Preparation

Metallography involves the study of structure and constitution of metals and alloys. Although, a lot can be learned from the observation and examination of specimens with the naked eye, the application of more sophisticated techniques help the analysis process.

This is why there's an increased requirement for magnification and preparation of the material’s surface. For general purpose examination, the use of Optical microscopy is sufficient whereas for advanced examination needs in metallographic analysis, the application of high-end research laboratories is a necessity.

Labs containing electron microscopes (SEM & TEM), electron diffractometers and X-ray are what is needed. If the implied technique for sample preparation is incorrect for metallographic analysis, then it can result in changing the original microstructure of the material and most likely deliver erroneous outcomes.

Sectioning – The Preliminary Step in Metallography Sample Preparation

This is the first step in sample preparation where the specimen which will be analysed later will be cut or sectioned off from the primary material source. While carrying out this step, the metallurgist has to make sure that they don’t alter the microstructure or damage any fracture features during the specimen cutting.

This is why the use of right sectioning equipment is of immense importance. If an abrasive saw is used for cutting or sectioning then it is essential to keep the specimen cool with the use of appropriate lubricant or coolant.

The damage or error caused during sectioning is usually related to the material that is being sectioned along with the cutting device’s nature, the cutting speed, the type and amount of coolant used.

Abrasive cutting method is the most widely used sectioning procedure. This specific technique utilises low-speed cut-off wheels especially in cases where the heat generated by standard abrasive cutters must be prevented.

A cut-off wheel generally includes abrasive grains, for example, silicon carbide or aluminium oxide which are bonded together with rubber or any other material to form a thin wheel. For wet operation, the rubber bonded wheel is mostly used and for dry cutting, the resin bonded wheel is used.

In some special cases, diamond and grinding cut-off saws are utilised for sectioning of materials while at the same time retaining smooth cut surface which is ideal for suitable grinding and polishing.

Other than abrasive cutting, the other sectioning method used is utilisation of band saw. Although it is rarely used, when this method is applied, experts usually prefer handheld band saw for executing rough sectioning. The reason for the usage of handheld saw is because it doesn’t generate enough frictional heat to change the microstructure.