Metallography

We are proficient in all phases of metallographic sample preparation. There are more than 40,000 different alloys of metals. Each metal has a different etched microstructure. The photomicrograph shown is an etched copper grain that has been deformed. Metallographic sample preparation consists of cross-sectioning a sample, encapsulating the desired surface in a 1¼" diameter Lucite mount. The surface is first rough ground on a wet silicon carbide disc. The sample is then sanded on four silicon carbide paper grits, starting at 220 grit and finishing with 600 grit. The surface is then polished on a nylon covered wheel with 6 micron diamond paste. The last polish is on a rayon cloth wheel with .05 micron alumina. At this point, the metal surface has a mirror finish. Depending on the alloy, the surface is then etched with a suitable acid to bring out the microstructure. The majority of metals are prepared in this manner. Some special alloys require other techniques. Metallography is useful in determining heat treatment of steel; detecting cracks in the microstructure; porosity; weld fusion; metal grain size; plating thickness; examining anodized protective surfaces on aluminum; and measuring wall thickness on copper water pipes. In many instances examination of the etched microstructure in steel alloys can help us determine what type of steel we are looking at. The prepared samples are viewed through a microscope called a "metallograph," shown in the second photo.

Note the black metallograph shown is one of the first scopes used in the San Francisco Bay area. This metallograph was used by one of the first heat treaters in Oakland in the 1920s and 1930s.