Study of the Influence of Variation in the Number of Layers in Multilayer Aluminium Nitride-Titanium-di-oxide Coatings on Resistance to Thermal Effects and Cavitation Erosion

Abstract

The paper presents the results of tests on the corrosion resistance of AlN – TiO2 coatings used as anti-corrosion protective coatings for the protection of oil and gas pipelines, and also determines the role of variation in the number of cycles in coatings on resistance to external influences, including aggressive environments and the presence of impurity deposits during cavitation erosion tests. Samples of AlN – TiO2 coatings were obtained using the magnetron sputtering method, by alternating layers, which made it possible to obtain multilayer coatings with a different number of layers in the coating composition at maintenance of the overall thickness for all samples. The resulting changes in mechanical strength characteristics depending on the type of impact during cavitation erosion tests have led to the conclusion that it is possibile to use multilayer coatings to protect against the impact of aggressive environments and vibrations during operation. At the same time, differences in changes in the values of the degradation degree of strength parameters for AlN – TiO2 coatings depending on the number of layers indicate the possibility of variation of the composition of coatings depending on their operating conditions. It has been established that in the case of the layer number growth from 15 to 40, the resistance to vibration in aggressive environments for 40-layer coatings is higher than for 15-layer coatings, despite the lower adhesive strength indicators in the initial state. Based on the results of the studies conducted, it was established that elevation of the temperature of model solutions from 25 °C to 90 °C leads to an increase in the mechanical and chemical processes of degradation of the near-surface layers due to the surface destabilization as a result of the intensification of the impact of cavitation bubbles and abrasive particles at addition of impurity inclusions to the composition. At the same time, multilayer coatings with 15 – 20 layers have high resistance to cavitation erosion, both in the case of low-temperature tests and at elevated temperatures.