Interfacial mechanical properties and fracture morphology of a TiN-coated steel wire upon tensile loading

The state of stress in a TiN-coated stainless steel wire upon tensile loading was analyzed theoretically using a classical model of continuum elasticity, from which the interfacial mechanical properties of the coating system were deduced. Specimens for the tensile test were prepared by deposition of TiN films on stainless steel wires using a hollow cathode discharge ion plating (HCD-IP) coater. Cross-section SEM shows that the TiN produced by the ion plating technique has good coverage on the steel wires and that the thickness ratio between the thickest and the thinnest coatings is 3.57. The failure mechanism of the TiN films upon tensile loading is found to depend on the coating thickness. Opening mode prevails in the thick coatings where periodic cracks perpendicular to the tensile axis developed; on the other hand, shearing mode takes place in the thin coatings where cracks inclined to the tensile axis by 45 degrees occurred. On the basis of the experimental observations and the theoretical calculation, the shear strength of the TiN, the ultimate shear strength and the bonding strength of the TiN/steel interfaces were estimated to be 15.36, 9.87 and 1.06 GPa, respectively. (C) 2000 Elsevier Science S.A. All rights reserved.