Metallographic analysis is an important research method in materials science, mainly used to observe the microstructure (tissue) of metals and their alloys, thereby evaluating the properties, processing history, and defect conditions of materials. Through metallographic analysis, it is possible to understand key information such as grain size, phase composition, inclusion distribution, and crack propagation path, which is of great significance for material quality control, process improvement, and failure analysis.



One, Basic Process of Metallographic Analysis



The process of metallographic analysis mainly includes the following steps: sampling, mounting, machining, polishing, etching, and microscope observation.



1. Sampling

According to the specific situation of the material to be analyzed, select representative samples. The sampling location should avoid areas severely affected by deformation or heating to ensure the authenticity of the observation results.



2. Mounting

For specimens with irregular shapes or small sizes, it is usually necessary to perform mounting to make it easier for subsequent operations. Commonly used mounting materials include thermosetting resins and cold mounting resins.



3. Machining and Polishing

Machining is the process of progressively grinding the surface of the specimen with sandpaper of different particle sizes to remove the damaged layer caused by cutting or processing. Subsequently, mechanical polishing is performed using diamond polishing agents and polishing cloths to achieve a mirror-like surface on the specimen.



4. Etching

Etching is a key step in revealing the microstructure of metals. Through the selective etching action of chemical etchants, the grain boundaries, phase boundaries, or differences in tissue composition are made apparent. Common etchants include nitric acid alcohol solution, picric acid solution, etc., and the specific selection is based on the type of material.



5. Microscope Observation

Use metallographic microscopes or electron microscopes to observe the treated specimens at high magnification, record the tissue characteristics, and analyze them.



Two, Key Factors in Tissue Observation



In the process of metallographic analysis, there are many factors that can affect the effectiveness of tissue observation:



- The control of the etching time is crucial; too short and the tissue is not clear, too long may lead to excessive etching, covering the true tissue.

- The quality of polishing directly affects the clarity of the image, and scratches, reliefs, and other phenomena should be avoided.

- The magnification of the microscope needs to be selected according to the characteristics of the tissue, generally ranging from 100 times to 1000 times.

- When observing, it is necessary to combine standard metallographic charts for qualitative and quantitative analysis.



Three, Applications of Metallographic Analysis



Metallographic analysis is widely used in metallurgy, machinery, aerospace and other fields. For example, in the steel industry, by observing the structures such as austenite, ferrite, pearlite, and martensite, the heat treatment state of the material can be determined; in casting inspection, defects such as shrinkage holes, bubbles, and inclusions can be identified; and in failure analysis, it helps to analyze the origin and propagation path of cracks.



Four, Conclusion



With the development of materials science, metallographic analysis technology is also continuously advancing. Combined with modern technologies such as image analysis systems and scanning electron microscopes, it makes the observation and analysis of microstructures more precise and efficient. Proficient in metallographic analysis technology not only helps to understand the properties and behavior of materials but also provides a solid foundation for the development of new materials and engineering applications.