Replication Microscopy Techniques for NDE

SURFACE REPLICATION is a welldeveloped electron microscopy sample preparation technique that can be used to conduct in situ measurements of the microstructure of components. The in situ determination of microstructural deterioration and damage of materials subjected to various environments is an objective of any nondestructive evaluation (NDE) of structural components. The need to assess the condition of power plant and petrochemical metallic components on a large scale recently led to the application of surface replication to the problem of determining remaining life. The usual method of metallographic investigation, which may involve cutting large pieces from the component so that laboratory preparation and examination can be performed, usually renders the component unfit for service or necessitates a costly repair. As a result, metallographic investigations are avoided, and important microstructural information is not available for evaluating the component for satisfactory performance. Therefore, an in situ or field microscopy examination is needed to aid in the proper determination of component life. The replica technique for the examination of surfaces has been extensively used for studying the structure of polished-and-etched specimens and for electron fractographic examination (see the article "Transmission Electron Microscopy" in Volume 12 of the 9th Edition of Metals Handbook for a discussion of replication techniques in fractography). Surface replication was the predominant technique in electron microscopy prior to being supplemented by thin-foil transmission and scanning electron microscopy. Recently, the replication microscopy technique has become an important NDE method for microstructural analysis, and an American Society for Testing and Materials specification has been written for its implementation (Ref 1).