A study of the interfacial structure between the TiN film and the iron nitride layer in a duplex plasma surface treatment

The so-called 'black' layer between PVD TiN coating and an ion nitrided surface was observed by SEM and TEM to investigate the detailed microstructure of the interface and the delamination mechanism of the TIN film. Two distinct sublayers were observed in the black layer. The upper sublayer was of very fine grains and the lower region of 10 times larger grains. The fine grains were irregular and around 50 nm in size. The larger grains of the lower sublayer were similar to the compound layer underneath. A Ti-based film was deposited on the surface of the black layer during Ti ion bombardment in a cathodic are ion plating method and identified as TiN and Ti phase. The TiN him deposited during Ti ion bombardment was of a very fine grain size and had a strong preferential arrangement of (200) plane perpendicular to the surface. A lot of gores were observed along the interface between the TiN film and the upper sublayer. It is suggested that the cracking and delamination of the TiN sim be initiated at these pores during the scratch adhesion test, which thereby decreased the adhesion strength of the TiN film. (C) 1999 Elsevier Science S.A. All rights reserved.