The use of metal materials usually follows the relationship of “component-structure-property”. Metallography is the science of studying the internal structure of metals or alloys. Metallography is the study of the microstructure of various metal alloys. It can be more precisely defined as the discipline of observing and judging the chemical and atomic structure and spatial distribution of grains, compositions, inclusions, or phases in metal alloys. Metallographic microscopes are essential tools for the study of the microstructure of metals and alloys. They allow us to see the tiny details of the metal’s structure, which can provide valuable information about its properties and performance. In this comprehensive guide, we will discuss the main features of metallographic microscopes, the process of metallographic sample preparation, and the applications of metallographic microscopes.
What Are the Main Features of the Metallographic Microscope？
The metallographic analysis adopts the principle of quantitative metallography and determines the three-dimensional spatial morphology of the alloy structure by measuring and calculating the metallographic microstructure of the ground surface or thin film of a two-dimensional metallographic sample, thereby establishing a quantitative relationship between alloy composition, structure, and properties.
Understanding the relationship between microstructure and macroscopic properties plays a key role in the development and fabrication of materials, which are the ultimate goals of metallography.
A material’s performance can be better understood by examining and quantifying its microstructure. Therefore, metallography is used at almost all stages of a component’s life: from initial material development to inspection, production, manufacturing processes, and even the required defect analysis. The principle of metallography is to ensure product reliability.
The metallographic microscope system organically combines a traditional optical microscope with a computer (digital camera) through photoelectric conversion. Not only can microscopic observations be made on the eyepiece, but also real-time dynamic images can be observed on the computer (digital camera) display screen. , computer-based metallographic microscope, and can edit, save, and print the required pictures.
What Is the Process of Metallographic Sample Preparation？
Metallographic samples are directly observed, analyzed, and studied under a microscope. The observation surface of metallographic samples has high requirements for smoothness, and it needs to be as bright as a mirror without scratches. In the process of metallographic analysis, sample preparation is a crucial link, which generally includes five processes: sampling, rough grinding, fine grinding, polishing, and etching.
Selecting appropriate and representative samples is an extremely important step in metallographic microscopic analysis. The selection of sampling locations and grinding surfaces should be determined according to the analysis requirements.
2. Coarse grinding
Rough grinding has three main purposes:
- Trim. Irregular-shaped specimens must be rough ground and trimmed into regular-shaped specimens.
- Smooth. The incision of the sample is often not smooth enough. To smooth the observation surface and remove the deformation layer produced during cutting.
- Chamfer. Without affecting the purpose of observation, the edges and corners on the sample need to be ground off to avoid scratching the sandpaper and polishing fabric (for samples that need to observe surface structures such as carburized layers and decarburized layers, the edges cannot be rounded. It is better to inlay).
3. Finely grind
After rough grinding, the specimen will inevitably have thicker and deeper wear marks on the grinding surface. To further eliminate these wear marks, fine grinding must be performed. There are two main types of fine grinding: manual grinding and mechanical grinding.
The purpose of polishing is to remove the fine grinding marks left on the grinding surface after fine grinding and obtain a smooth mirror surface. Commonly used polishing methods include mechanical polishing, electrolytic polishing, and chemical polishing.
If the polished sample is directly observed under a microscope, only a bright light can be seen. Except for some non-metallic inclusions (such as MnS and graphite, etc.), the various components and their morphological characteristics cannot be identified. It must be used Only when the etchant “etches” the surface of the sample can the true microstructure be seen.
There are many etching methods, the most commonly used is chemical etching, which uses the chemical dissolution and electrochemical etching of the sample by the etching agent to expose the tissue.
What Are the Applications of the Metallographic Microscope?
Metallographic microscopes can be used to identify and analyze the structure of various metals and alloys. They are widely used in factories or laboratories to identify the quality of castings, inspect raw materials, or research and analyze the metallographic structures of materials after processing. It can also be used for inspection and measurement of semiconductor testing, circuit packaging, precision molds, biological materials, etc.
Metal alloys play a prominent role in many technologies and applications due to their wide range of properties. There are currently several thousand standardized alloys available, and this number continues to grow as new needs develop that may require new alloys. Metallography is the study of alloy microstructure, which includes: phase state, microscopic spatial distribution of inclusions, and other components. Various techniques, often microscopes, have been used to reveal the microstructure of alloys. The microstructure of an alloy has a significant impact on many of its important macroscopic properties, such as tensile strength, elongation, and thermal or electrical conductivity. A thorough understanding of the relationship between microstructure and alloy properties is fundamental to the field of metallography. Metallographic knowledge is used in metallurgy (alloy design and development) and alloy production. Metallographic microscopes are essential tools for understanding the microstructure of metals and alloys. Scopelab is a leading supplier of metallographic microscopes. For more details, please contact us.