A specimen preparation technique for atom probe analysis of the near-surface region of cemented carbides

Methods to prepare specimens for APFIM analysis of the near-surface region have been studied. We used a WC-TiC-Co based material with a composition gradient near the surface. The methods were also applied to a CVD multilayer coated cutting tool insert. It was our intention to develop a preparation method in which a specimen could be used more than once by back-polishing. Our conclusion was that several different techniques have to be involved. The method we propose is divided into three steps. First of all a specimen blank has' to be prepared with a coating covering the surface. This coating will serve as a protection layer during polishing and as a marking layer that can define the surface. The blanks are then polished mechanically as much as possible by dimple grinding. Final shaping of the tip is achieved by alternating pulse polishing and ion milling. Our aim is to get a tip from less than ten micrometers under the surface and so far we have managed to prepare a tip 19 +/- 2 mu m from the surface. An atom probe analysis of this specimen is presented.