Development of Atom Probe Specimem Preparation Techniques for Specific Regions in Steel Marterials

The three-dimensional atom probe (3D-AP) is a very useful tool for quantitative observation of atomic position and concentration of all alloying elements in steel. However, the very small analysis volume of the atom probe (~20 nm times 20 nm times 100 nm) has limited application. It was difficult to produce a needle specimen with a tip containing the specific region by randomly sampling with the normal electro-polishing. To extend the application field to steel, the development of needle specimen preparation techniques of specific regions is required. In this work, a progressive sampling technique for 3D-AP using a focused ion beam (FIB) fabrication with a sample lift-up system (micro-sampling method) is developed . The technique enables atom probe analysis of any localized position of the sample. 3D-AP analyses for bainite/ferrite interface in low carbon steel, surface layers of the nitriding steel, and lamella structures of the drawn pearlite wire in the probing direction perpendicular to the lamella, are successfully accomplished