1. Inspection of samples

    Microscopic examination is performed by using artificial magnification for sample inspection to enhance the appearance of small features. This is the opposite of visual inspection, which involves using naked eyes to inspect the sample;

    Optical microscopy examination is used to examine microstructure at a magnification of up to 1000 times. Electron microscopes with a magnification of up to 500000 times are commonly used for failure analysis in research and development laboratories and educational institutions;

    2. Microscopic examination type

    Four types of microscopes were used for metallographic material testing, depending on the nature of the sample and the object of observation;

    light microscopy

    In optical microscopy, different filters are used to improve contrast and enhance specific features based on material properties. This can usually be achieved using a magnification range of 2.5 to 1000 times. In metallography, reflected light is the most commonly used type of optical microscope examination. Emission optical microscopy can also be used for inspection, but it is mainly used for mineral samples;

    Stereoscopic optical microscopy

    Stereoscopic microscopy is an optical microscope examination that uses light reflected from the surface of a sample to observe the sample at a low magnification;

    Scanning electron microscope inspection

    Scanning electron microscope (SEM) is a kind of electron microscope inspection. Focused electron beam can be used to scan the surface of the sample to generate an image of the sample. The interaction between electrons and atoms in the sample generates various signals that can be converted into information about the surface morphology and composition of the sample;

    Transmission electron microscopy inspection

    Transmission electron microscopy (TEM) uses an electron beam to project an ultrathin specimen and interact with it as it passes through it. The generated signals can be converted into various types of information, including information about the type and orientation of each crystal;

    3. How to perform optical microscope inspection

    Sample preparation:

    The surface condition of the sample will affect the reflection or propagation of light. The acceptable level of this effect depends on the type and size of features related to the inspection, and correct sample preparation is crucial for obtaining the required surface quality and contrast;

    Light source:

    The image of a surface is based on the interaction between light and the surface. In terms of surface characteristics such as roughness, color, or alignment, different light sources such as LEDs, halogen lamps, or mercury lamps, as well as different lighting types such as coaxial, annular, or point light sources, will cover many different surfaces to be inspected;

    Correct lighting is crucial for investigating complex configurations;

    Filter:

    Bright Field (BF) comparison is the most commonly used comparison technique. Only details with different reflectivity can distinguish each other;

    You can use contrast techniques such as dark field (DF), differential interference contrast (DIC), and polarized light (POL) to observe details different from those seen in BF;

    The selection of filters in optical microscopy depends on the surface properties and the characteristics and details to be investigated.

    4. Image acquisition

    In addition to the above methods, the acquisition of actual microstructure depends on important factors during image acquisition, with the two most important factors being exposure and white balance.