Inside Metallography

Metallographers are anatomists of metal. Whether it's the bronze of a 1,800-year-old arrowhead or a steel I-beam from WorldTrade Center Building 7, metallographers use a family of techniques for revealing metallic microstructures that tell stories.

Born in the second half of the 19th century, when iron and steel were ascendant in the constructed landscape, metallography was the brainchild of Henry Clifton Sorby in Sheffield, England. With the iron boilers of high-pressure steam engines exploding in factories and the wheels of railroad cars shattering with death-dealing results, learning what made metal go bad was becoming more urgent. To Sorby, this meant somehow looking inside the materials.

He took on this challenge by combining his own petrographical pursuits, in which he examined polished salami-like slices of rocks to study different mineral phases, with decorative acid-etching techniques from his family's business in cutlery. When applied to metal, the slicing, polishing, and etching procedure that he formulated uncovered, through a microscope, the inner anatomy of metal.

"You can infer a lot about the manufacturing process of a metal component, and what happened to it in service, by studying the microstructure," says longtime metallographer George F. Vander Voort, director of research and technology at Buehler, Lake Bluff, Ill., a global firm that specializes in materials-analysis equipment.

Today, thousands of behind-the-scenes metallographers around the world apply their craft for quality control, materials analysis and certification, failure analysis, and fundamental studies of what makes materials tick. On this and the following pages are examples of work by several metallographers. Each image tells a story, perhaps as small as how well a rivet was installed during the making of a ship. Sometimes the story has larger implications, like one partly told by a metallographic image produced from a sample of wrecked steel from the World Trade Center site.—IVAN AMATO

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