Microstructures and Adhesions of TiN Film Coated on White Layer

Adhesion strengths and microstructures of TiN coatings on white layer composed of epsilon nitride (Fe2-3N) were examined. In the present study a hot work tool steel, SKD61, was used for a substrate. The substrates were coated with TiN by physical vapor deposition (PVD). Specimens were prepared with changing the conditions for polishing the surface of the substrate, and conditions for nitriding before PVD treatment. Peeling of the coated film occurred on un-polished specimen surface. Other specimens can be coated with TiN film without peeling. The microstructures, phase identifications and adhesion strengths were investigated by scanning electron microscopy (REM), X-ray diffraction (XRD), scratch tester and Rockwell adhesion tester, respectively. The black layer formed between the TiN film and white layer was observed by SEM, which generally deteriorates adhesion strength. However the scratch tests showed that the adhesion strengths of the specimens with black layer were higher than those on the specimen without the black layer. The black layer would not always decrease the adhesion strength.