Important Features To Look For In A Metallographic Microscope

Metallography is the study and analysis of prepared metal surfaces primarily to reveal their microscopic structure and components. Metallographic samples are studied using either optical microscopes or electron microscopes. In order to be able to produce a correct assessment and identification of the material being studied, technicians require the use of a quality metallographic microscope. Some of its important features include:

Optical system
A quality optical system is the mark of an excellent metallographic microscope. This is the primary consideration to keep in mind when looking for this type of microscopy. Remember that the main concern of metallography is to analyze metal surfaces using a magnifying device, so it’s important that the microscope’s optical system meets the requirement.

The microscope’s magnification powers should start at 40x and have graduate magnification power lenses up to about 600x. If high magnifications are required, objective lenses of about 1000x are also available. As for the eyepiece, start with a low 10x or 15x. Choose eyepiece sets that offer a wide field of view. This will allow you to see a larger portion of the image.

Focusing mechanism

The focusing mechanism is another important feature of a metallographic microscope. While the primary job of the eyepiece and objective lenses is for magnification, the focusing mechanism works to refine the image of the object being observed.

Illumination
There are different illumination techniques used in metallographic microscopes. These include bright field, dark field and polarized light, among others. Some metallographic research microscopes are equipped with all four types, while others may be supplemented with the appropriate accessories.

Bright field microscopy is the most common type of metallographic microscope. It uses light to light up the sample material. Light is then bounced back through the eyepiece to produce a magnified image.

Dark field microscopy, although not popularly used these days, provides excellent resolution and high contrast, compared to bright field. Instead of allowing light to reflect itself to the eyepiece, this type of metallographic microscope blocks this light. A small amount of light is received, entering the objective lens and produces a high contrast image. Basically, features that look dark using bright field microscopy will look bright with dark field. Any clear area in the sample including the background will appear dark.

Polarized light metallographic microscopes are excellent for observing metallic microstructures which are non-cubic by nature, such as crystal structures characterized as hexagonal close-packed or hcp. Polarized light microscopy can also effectively produce images of hcp metals that have been etched using chemicals such as chromate and sulfide.

Illumination
The source of light is key to the proper observation of the sample material. Look for a metallographic microscope with a variable intensity light. Two of the most common types of light bulbs used with microscopes are fluorescent and halogen bulbs. Fluorescent bulbs provide a sharp, white light while halogen bulbs provide a more natural light, similar to sunlight. Make sure that the wattage is sufficient to illuminate the sample. Certain types of microscopy, such as dark field, require strong lighting in order to produce an effective image.

Usage
If the microscope will be used mostly outdoors, a field metallographic microscope is the better choice. This is a waterproof, portable, light and sturdy instrument that is designed to withstand transport, wear and tear and most conditions in an uncontrolled environment.

Ergonomics
Most quality metallographic microscopes these days are ergonomically designed, which is preferable if long hours of work will be spent studying samples. Look for an angled head (preferably binocular) and a turret that can be rotated a full 360 degrees. If the metallographic microscope is binocular, choose one with adjustable heads, to allow the user to find the most comfortable distance between the eyes.

Electron microscopy for metallographic studies
For serious metallographic study, probably the high end instrument to have is the electron microscope. There are two different types of electron microscopes used for metallography. These are the SEM (scanning) and the TEM (transmission). Electron microscopes can be an excellent tool to use for metallography, but they are not always the first choice. Initial studies and analyses of sample materials often involve the use of light optical microscopy and not always with electron microscopy. This is because light optical microscopes allow faster inspection. They are also less expensive. Certain features of the metals, especially the colors, are also best viewed using this type of microscopy.

The tiny structures and components of the material are also more evident in light optical microscopes but not in electron microscopes, since the former uses lower magnification power. At less than 500x, these structures can already be viewed quite easily, whereas an electron microscope requires at least 2000x. As a metallographic microscope, electron microscopy can present highly magnified images of the sample. However, it is also very costly to buy and operate. Furthermore, electron microscopes are mostly used as research microscopes. For hobby, amateur or educational use, other metallographic microscopes will do.