Microstructure and properties of metal/ceramic and ceramic/ceramic multilayer coatings on titanium alloy Ti6Al4V

Abstract

The paper presents results concerning microstructure and mechanical properties of the metal/ceramic and ceramic/ceramic multilayer coatings obtained on Ti6Al4V alloy by the PVD (Physical Vapour Deposition) vacuum arc method. During the work Cr/CrN, Ti/TiN and CrN/TiN multilayer coatings were deposited with the similar total thickness but a different number of constituent layers. Focus ion beam sample preparation followed by STEM (Scanning Transmission Electron Microscopy) observations were performed in order to analyze the influence of phase composition and the number of layers on the microstructure of multilayer coating. The effect of these parameters on the hardness and Young modulus of the coatings obtained by nanoindentation technique was also investigated. These results were then used to calculate the values of elastic strain to failure (H/E) and resistance against plastic deformation (H3/E2).The results revealed that the obtained multilayer coatings differed in microstructure due to the different type of interfaces. Coherent, semi-coherent interfaces or interfaces with a transition layer influence the growth mechanism of the coatings and affect grain size. The investigation revealed that the grain size of the coatings also depends on the bi-layer period (number of layers). However, this effect was opposite for the metal/ceramic and ceramic/ceramic coatings due to the type of interface. The results showed that increasing the number of layers improved the mechanical properties of the Cr/CrN multilayer coatings. However, this relationship was not observed for CrN/TiN.