In various fields of industry, a necessary condition for the development and production of metal products is a comprehensive study of their microstructure. At different stages of production, technologists study the characteristics of raw materials, blanks, parts and end products, which allows us to successfully improve the properties of materials and detect defects in a timely manner. In recent years, the tasks of such studies are increasingly entrusted to optical technology and, in particular, to the metallographic microscope, which is used to study opaque objects in reflected surfaces.
For the most part, such devices are used in areas involving the performance of certain operations with metals. In particular, they are used by geologists, archaeologists, metallurgists and specialists from various fields.instrumentation and electronics, where accurate analysis of conductors is important. What information does a microscope give for metallographic studies? This device allows in reflected light to form a structural configuration of the placement of material grains, to fix the presence of foreign particles in it, to determine the characteristics of the surface layer, etc. From the point of view of defectology and non-destructive testing, this is extremely important information that gives an idea of the flaws in the external minute details about dimensional parameters, crystal structure and even about some chemical properties. For example, this method of analysis reveals the smallest shells, cracks, lack of penetration and other defects.
Design of the apparatus
The basic device of the device consists of three parts, which include the lighting module, the central unit and the table. The lighting part is a lamp or lantern, which is fixed on an adjustable swivel bracket, and also has its own energy supply. The same part of the metallographic microscope includes a group of light filters with different colors. As for the central block, it houses several functional components at once, including a prism optical system, an illuminating tube, object tables, regulatory mechanisms, eyepiece attachments and auxiliary means for organizing technical operations in the process of work. All of the above infrastructure is placed on a carrier base - a microscope table, whichcontains an optical bench and various drawers with cabinets in which the accessories of the apparatus are stored.
The main task of the device is to process the parameters of the radiation reflected by the surface of the object. For this, the aforementioned optical system is used, which captures the slightest changes in the aperture diaphragm against the background of regulation of the object's illumination parameters. In a sense, the working factor of measurement is the course of the rays, which manifests itself differently in bright and dark fields. For example, when studying in a bright field, the rays coming from the lamp pass through the diaphragms (field and aperture) and are directed to the reflective plate. The latter, in turn, reflects the characteristics of the structure under study, partially transferring the light to the target product with the help of a lens.
When observing objects in a dark field, an optical metallographic microscope interacts with a parabolic mirror-reflecting surface, an annular diaphragm and a folding lens. The extreme beams of radiation, bypassing the diaphragm, are directed to the annular mirror, covering the plate with the reflector. From this moment on, the mirror begins to reflect light onto the condenser, redirecting the rays to the plane of the object. The image will be formed based on the characteristics of the reflected rays that have passed through the lens and entered the optical tube.
Specifications of the metallographic microscope
The working process of the device is characterized by two groups of parameters - these are the indicators of the lens andeyepiece. The main operating parameters of the lens are:
- Magnification ratio - from 11x to 30x in bright field conditions, and from 30x to 90x in dark field studies.
- Numerical aperture - from 0.17 to 1.3.
- Focal length – 2.4 to 23 mm on average.
- Free distance - from 0.13 to 5.4 mm.
In the case of the eyepiece of a metallographic microscope, there are two key characteristics to highlight:
- Focal length - from 12 to 83 mm.
- Linear field of view - 8 to 20mm.
Before using the instrument, it is necessary to adjust the frame or working platform of the structure, open the aperture diaphragm, adjust the mechanical fasteners and move the analysis manifold to the lamp. If a portable metallographic microscope is used, then the software will help to achieve the optimal combination of eyepiece and objective settings, since portable models of the device provide for the ability to connect to computer stations directly in the laboratory. One way or another, before starting work, it is recommended to set the magnification scale in the range from 500 to 1000 apertures. Then you can move on to optical filters, which are selected according to the characteristics of achromatic lenses. In this case, the universal solution will be a correction for the midtones of the visible part. Only a yellow-green light filter is not combined with apochromats. After setting, the process startsoptical data processing of the formed image, the graphic materials of which are subsequently sent for decoding in accordance with the analysis tasks.
Technology of metallographic research has a rather narrow specialization, which does not reduce the great value of this method of studying surfaces. To meet consumers in the form of industrial enterprises with their laboratories, the developers of the device themselves go, improving its performance. For example, the domestic METAM-P1 metallographic microscope costing about 13 thousand rubles. rich in equipment and the presence of modern high-tech features. Suffice it to note that it is provided with sets of planachromat objectives and compensatory eyepieces with wide optical ranges. And this is just the basic version in one of the families of new generation metallographic aggregate microscopes.