Explanation of Application Fields of Metallographic Microscope
Application Fields of Metallographic Microscope
Ferrous metal metallographic examination, non-ferrous metal metallographic examination, powder metallurgy metallographic examination, tissue identification and evaluation after material surface treatment.
Material selection: There is a certain correspondence between the microstructure and properties of materials, based on which suitable materials can be selected.
Verification: Raw material verification and process verification.
Spot check: The product manufacturing process conducts metallographic inspection on semi-finished products to ensure that the microstructure of the product meets the processing requirements of the next process.
Process evaluation: Determine and identify the conformity of product processes.
In service evaluation: Provide a basis for the performance, reliability, and service life of in-service components.
Failure analysis: Discovering process and material defects to provide macro and micro analysis basis for the analysis of failure causes.
The imaging principles of metallographic microscopy
1. Bright and dark fields of view
A bright field of view is a basic observation method for observing samples under a microscope, presenting a bright background in the field of view area of the microscope. The basic principle is that when the light source is vertically or approximately vertically illuminated onto the surface of the sample through the objective lens, it is reflected back to the objective lens to create an image.
The difference between dark field illumination and bright field illumination lies in the presence of a dark background in the field of view area of the microscope. The illumination method of the bright field is vertical or vertical incidence, while the illumination method of the dark field is to illuminate the sample through oblique illumination from the surrounding area outside the objective lens. The sample will scatter or reflect the irradiated light, and the scattered or reflected light from the sample will enter the objective lens to make the sample image. Dark field observation allows for clear observation of colorless, small crystals or relatively light colored fibers that are difficult to observe in a bright field.
2. Polarized light, interference
Light is an electromagnetic wave, while electromagnetic waves are transverse waves, and only transverse waves exhibit polarization. It is defined as light that vibrates in a fixed manner relative to the direction of propagation of the electric vector.
The polarization phenomenon of light can be detected using experimental devices. Take two identical polarizers A and B, and pass natural light through the first polarizer A. At this point, natural light also becomes polarized light, but because the human eye cannot distinguish it, a second polarizer B is needed. Fix polarizer A, place polarizer B on the same horizontal plane as A, and rotate polarizer B. It can be observed that the intensity of transmitted light undergoes periodic changes with the rotation of B. The intensity of light gradually decreases from maximum to darkest at every 90 ° rotation, and then increases from darkest to brightest at every 90 ° rotation. Therefore, polarizer A is called a polarizer, while polarizer B is called a polarizer.
Interference refers to the phenomenon of light intensity strengthening or weakening caused by the superposition of two coherent waves (light) in the interaction zone. The interference of light is mainly divided into double slit interference and thin film interference. Double slit interference refers to the non coherent light emitted by two independent light sources. The device of double slit interference causes a beam of light to pass through the double slit and become two coherent beams, forming stable interference fringes on the light screen. In the double slit interference experiment, when the distance difference between a point on the light screen and the double slit is even multiple of the half wavelength, a bright stripe appears at that point; When the distance difference between a point on the light screen and a double slit is an odd multiple of half wavelength, the appearance of a dark stripe at that point is considered Young's double slit interference. Thin film interference refers to the interference phenomenon caused by two reflected light beams formed by a beam of light reflecting off two surfaces of a thin film. In thin film interference, the path difference between the reflected light from the front and rear surfaces is determined by the thickness of the film, so the same bright stripe (dark stripe) should appear in places where the thickness of the film is equal. Due to the extremely short wavelength of light waves, the dielectric film should be thin enough to observe interference fringes during thin film interference.
