Laser based etching technique for metallography and ceramography

The details of a new etching procedure developed using a pulsed Nd:YAG laser for revealing microstructures in metallic and ceramic specimens are presented. The new etching technique would be useful for applications on existing components, thin specimens and specimens under hostile environments, in a remote and non-contact manner. The technique has been applied on a variety of materials such as UO2, boron carbide, copper and Zircaloy-2, to demonstrate its wider applications. It has been found that the microstructures obtained using this new laser based etching (LBE) technique, many a time, have even better contrast, as compared to the chemically etched specimens. For example, in UO2 specimens, the porosity at the grain boundaries and within the grains have been clearly revealed by LBE. The microstructure of copper, obtained using the LBE, clearly reveals the grain boundaries, twins and sub grain features. Unlike conventional etching techniques, LBE requires only polishing up to 600 grit level, unlike the optical finish that is essential for chemical and electrochemical etching. In fact, the efficiency with LBE is found to be better when the surface has lesser than optical finish, because of the associated advantage of lower reflectivity of the surface for the incident laser beam.