References cited in this section

3. S.N. Chanat, A.M. Trujillo, and D.C. Zipperian, Advanced Techniques for High Speed Precision Sectioning, Buehler Digest, Vol 27 (No. 1), 1993

4. D.C. Zipperian and S.N. Chanat, Readying Advanced Composites for the Microscope, Adv. Mater. Proc., Aug 1993, p 15-21

5. D.C. Zipperian, S.N. Chanat, and A. Trujillo, Ceramic Microstructural Analysis for Quality Control, Am. Ceram. Soc. Bull., Vol 71, July 1992, p 1077-1098

6. G. Petzow, Metallographic Etching, American Society for Metals, 1978 Optical Microscopy

For lower magnifications, 25* to 1000*, the optical microscope is the most important tool for the study of microstructure.

For magnifications greater than 1000*, the scanning electron microscope is a useful tool. Today there are also other types of microscopes, including the scanning tunneling microscope and the confocal microscope.

The optical microscope offers a number of forms of illumination for revealing surface detail:

• Bright-field illumination is the most widely used. The incident light is reflected back through the objective, producing a bright background with dark features.

• Dark-field illumination is particularly useful for analyzing surface artifacts, such as surface scratches, and for studying grain structures. The incident light is supplied through the outside of the lens and is reflected back through the objective, producing a dark background with bright features.

• Oblique illumination is useful for low-magnification analysis that requires a three-dimensional appearance. It uses low-angle illumination, so higher magnifications are limited.

• Polarized light is especially useful for analyzing optically anisotropic metals, such as beryllium, Ct-titanium, and zirconium.

• Differential interference contrast (DIC) illumination is used to enhance topographic features in a surface. DIC illumination uses a Nomarski-modified Wollaston prism to split light into two wavefronts. Along with a polarizer, this enhances the relief effects on the surface.

Figures 3(a) to (c) show the same sample of machinable, reaction-bonded silicon-silicon carbide (SiSiC). In bright-field illumination, little information other than porosity is revealed, but in dark-field illumination, features such as grain boundaries and the porosity of the sample can be examined. In DIC illumination, the different phases of silicon and silicon carbide become very apparent.

Fig. 3 (a) Bright-field image of SiSiC. 200x. (b) Dark-field image of SiSiC. 200x. (c) Differential interference contrast illumination image of SiSiC. 200x

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