Alicja Krella

Degradation of protective PVD coatings

Abstract The aim of this chapter is to present and discuss the correlations between coating deposition and properties of physical vapor deposition (PVD) coatings, and the degradation mechanisms of hard coatings caused by dynamic loading. PVD coatings are very attractive for the aerospace, chemical, and oil and gas industries due to their anticorrosion properties, oxidation resistance, high hardness, and low coefficient of friction. Due to the fact that many devices during their service are exposed to shock loads, the knowledge of degradation mechanisms of PVD coatings under dynamic load is particularly important. PVD coatings have been successfully employed as wear-resistant coatings. They improve fatigue strength and cavitation erosion resistance. However, hard coatings easily fracture in a brittle mode. Mechanical behavior of coatings depends on which degradation mechanism dominates during deformation. Degradation mechanism is related on the coating structure (morphology, phase composition, number of layers in a coating, thickness of each layer, thickness of a whole coating), mechanical properties (Youngs modulus, hardness, adhesion) as well as on properties of substrate, and a rate and frequency of impacts. Moreover, in order to get a coating with special properties, composite or multi-layer coatings are produced. A tricomponent TiAlN or Ti(C,N) coating, combining the advantages of high hardness of TiC, high ductility of TiN, and high adhesion strength, possesses much better mechanical properties than single-phase TiC or TiN. Similarly, multi-layer coatings have shown better properties in many aspects than monolayer coatings, for example, cavitation erosion resistance of TiN/Ti multi-layer coating was better than single-phase monolayer TiN.

Al2O3 + TiO2 Thin Film Deposited by Electrostatic Spray Deposition

In the paper are presented the morphology of Al2O3 + TiO2 thin film produced by electrostatic spray deposition method and the results of investigations of its endurance when subjected to thermal cycles and slurry erosion. The film was produced in steam atmosphere by simultaneously spraying of colloidal suspension of Al2O3 nanoparticles in propanol-2 (as a solvent) with the addition of C10H20O5Si (to improve film adhesion) and 1 % solution of butoxy titanium Ti(OCH2CH2CH2CH3)4 in propanol-2 as a precursor of TiO2. Performed investigations showed that Al2O3 particles and TiO2 particles are uniformly distributed within the film, and that the weight content of aluminum and titanium is nearly the same. The thermal tests did not cause any fracture of the film but decreased film adhesion. Decreased adhesion of the film intensified degradation during slurry test.