Metallography is the study of the structure of metals and alloys using various techniques, especially optical and electron microscopy.(1) Metallography is used to reveal the microstructure of metals, which is affected by composition, processing conditions including heat treatment and cold working, and post-processing variables such as machining, loading and welding. Service environment also affects microstructure and problems such as corrosion, stress corrosion cracking, carburization, sulfidation and a host of other effects can be determined from a material’s microstructure. Metallography is a key element in many failure investigations and often provides the critical evidence needed to make a definitive determination of cause of failure.
Metallurgical mounts are generally made of a cross section through a material. The area in question is selected. The piece is cut in cross section and mounted in a suitable medium. The mount is then polished to a mirror finish. The sample can then be viewed via optical or electron microscopy. Often it is necessary to etch the sample in order to reveal its microstructure. This process is illistrated in the case study section below. At CTL, our metallurgical mounts are made in conformance to ASTM specifications.(2)
(2) ASTM E 3 – 01 “Standard Guide for Preparation of Metallographic Specimens”, ASTM International, West Conshohocken, PA 2001.