How to use a metallographic microscope:
Overview of metallographic microscopy tests
Metallographic analysis is one of the main methods for studying the internal structure and defects of metals and their alloys. It occupies a very important position in the field of metallic materials research. The method of using a metallographic microscope to magnify 100 to 1500 times on specially prepared samples to study the structure of metals and alloys is called metallographic microanalysis. It is the most basic experimental technique for studying the microstructure of metal materials. Microscopic analysis can study the relationship between the structure of metals and alloys and their chemical composition; it can determine the microstructure of various alloy materials after different processing and heat treatments; it can determine the quality of metal materials, such as various non-metallic inclusions --The quantity and distribution of oxides, sulfides, etc. in the structure and the size of metal grains, etc.
In modern metallographic microscopic analysis, the main instruments used are optical microscopes and electron microscopes. Here is only a general introduction to commonly used optical metallographic microscopes.
Purpose of the experiment: Understand the structure and use of ordinary metallographic microscopes; learn to use metallographic microscopes for microstructure analysis.
Structure and operation of metallographic microscopes
There are many types and models of metallographic microscopes, the most common ones are desktop, vertical and horizontal. Metallurgical microscopes usually consist of three major parts: optical system, lighting system and mechanical system. Some microscopes are also equipped with photography devices. Now take the 4x metallographic microscope as an example to illustrate.
Lighting system: There is a low-voltage (6~8v, 15v) light bulb in the base as a light source, which is powered by a transformer to reduce the voltage. The brightness of the light is changed by adjusting the secondary voltage (6~8v). The spotlight, aperture diaphragm and reflector are all installed on the circular base, while the field diaphragm and another condenser are installed on the bracket. They constitute the illumination system of the microscope, so that the surface of the specimen can be fully and evenly illuminated. .
Microscope focusing device: There are coarse and fine focusing handwheels on both sides of the microscope, both at the same location. As the coarse adjustment handwheel 6 rotates, the curved arm supporting the stage moves up and down. There is a braking device on one side of the coarse adjustment handwheel to fix the position of the stage after the focus is correct. Fine-tune handwheel 5 to make the microscope move slowly along the track. There are graduation grids engraved on the right handwheel, and each grid represents a slight movement of 0.002 mm up and down the objective lens holder. There are two white lines engraved on the gear box on the same side as the dial to indicate the micro-movement lifting range. When it reaches the extreme position, the micro-hand wheel will be automatically restricted. At this time, it cannot continue to rotate but should be reversed. to use.
Stage: used to place metallographic specimens. There are guide rails between the stage and the tray below. Pushing by hand can make the stage move crosswise within a certain range on the horizontal plane to change the observation position of the specimen.
Aperture diaphragm and field diaphragm: The aperture diaphragm is installed on the lighting reflector holder. Adjusting the aperture diaphragm can control the thickness of the incident light beam to ensure that the object image is clear. The field diaphragm is located under the objective lens holder. Its function is to control the field of view so that the field of view in the eyepiece is bright without shadows. There are also two adjustment screws on the straight-grained ferrule for adjusting the center of the diaphragm.
Objective converter: The converter is spherical in shape and has three screws on it, which can be used to install objective lenses with different magnifications. Rotating the converter allows each objective lens to enter the optical path. When used with different eyepieces, various magnifications can be obtained.
Eyepiece tube: The eyepiece tube is installed at a 45-degree tilt on a hemispherical base with a prism. The eyepiece can also be turned 90 degrees horizontally to coordinate with the camera device for metallographic photography.
The metallographic microscope is a precision optical instrument that requires careful use. Before working with a microscope, you must first be familiar with its structural characteristics and the mutual positions and functions of each main component, and then operate according to the microscope's usage procedures.
