Microstructure and coating properties of ion-plated TiN on type 304 stainless steel

Abstract

The microstructure and chemistry of TiN coatings on type 304 stainless steel were characterized by using a Zeiss EM 902A energy filtering transmission electron microscope equipped with an electron energy loss spectroscopy (EELS) detector. Thin TiN films were produced by a hollow cathode discharge ion plating coater. It was found by plan-view transmission electron microscopy that the microstructure of the TiN coatings is thickness-dependent. The grain size of TiN ranges from 88 nm at the coating surface down to 9 nm near the TiN-steel interface. In addition, the TiN surface layer shows some degree of texture, but the sub-surface and internal TiN layers are mainly equiaxial and randomly oriented. Chemical analysis by EELS shows that the relative oxygen content increases approximately from the TiN surface to the TiN-steel interface, whereas the relative nitrogen content first decreases slowly and then drops rapidly near the interface. The presence of a Ti2N phase and the deficiency of nitrogen near the TiN-steel interface suggest that the early-deposited TiN is non-stoichiometric. By the periodic cracking method, the ultimate shear stress at the TiN/steel interface and the residual stress in the TiN thin film were estimated to be 2.2 and 12.8 GPa, respectively. (C) 1998 Elsevier Science S.A. All rights reserved.