Investigation concerning the cavitation resistance of TiN coatings deposited on austenitic stainless steel at various temperatures

Abstract

TiN coatings were deposited on austenitic stainless steel, X6CrNiTi18-10, by means of the cathodic arc evaporation method at three different substrate temperature: 200 °C, 350 °C and 500 °C. All coatings were found to have strong (1 1 1) crystallographic orientation and fine crystalline structure of the δ-TiN phase. The substrate temperature was found to have an influence on the hardness and Young's modulus of the TiN coatings. Investigation of nanocrystalline TiN coatings resistance to cavitation was performed in a cavitation tunnel with a slot cavitator and tap water as the medium. The estimated cavitation resistance parameters of the coatings were the incubation period of damage, and total mass loss. It was found that the optimal coating cavitation resistance was deposition at 350 °C. The incubation period was the longest and the total mass loss was the least for deposition at 350 °C. The incubation period for the 350 °C deposition coating was approximately 100% longer than that of the uncoated X6CrNiTi18-10 steel and the total mass loss was significantly lower than that of the uncoated specimen. The scanning electron microscope analysis indicated that the damage process of the TiN coating mainly originates from the plastic deformation of the steel substrate– hard coating system, which appears by “micro-folding” of the surface. An increase of tensile stresses at the tops of micro-folds initates microcracks and delamination of TiN coating. The results of the investigation and the analysis indicate that the factors mainly responsible for cavitation resistance of the steel substrate/ hard coating system are resistance to plastic deformation of the total system and coating adhesion.