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Potentialities of HiPIMS in decorative applications

For both protective and decorative purposes, ceramic coatings such as TiN, CrN, ZrN, TiCN, TiCNbN etc are usually used. For example, TiN and ZrN stoichiometric coatings have golden colour with difference between both coating materials being in brightness [1]. TiCNbN compound for example exhibits a white colour [2]. All these coatings play an important role in industrial sector because of the improvement of surface properties that they provide but also because of their good appearance. Figure 1 shows WC inserts (uncoated (1), coated with TiN (2) and coated with TiCN/TiCNbN (2)).

This figure  shows the differences in color for uncoated tungsten carbide (WC) inserts (1), tungsten carbide insert coated with conventional TiN layers (2) and a tungsten carbide insert coated with the TiCN/TiNbCN multilayer system (3) (For more information please  refer to reference 2)
Figure 1: (WC) picture: (1) uncoatedWC insert, (2) tungsten carbide inserts (WC) coated with conventional TiN layers, (3) tungsten carbide inserts (WC) coated with TiCN/TiNbCN multilayer [2]

Magnetron sputtering, a physical vapor deposition (PVD) in which the coating vapor is created by energetic particle bombardment (sputtering) and is transported subsequently to the substrate, can be used to produce these coatings.

This can be done by sputtering a target (source of the coating) made of the compound material which is a good thing especially if the chemical composition of the desired colour is known, meaning that a target material of that composition can be made and will be reproduced exactly with that composition as a coating.

However, reactive magnetron sputtering can also be used in which a range of ceramic materials can be created by sputtering a low-cost metal target and admitting, in addition the inert working gas, a suitable reactive gas to the deposition chamber. This allows also to control the chemical composition and thus the colour.

However, as the reactive gas is introduced to the chamber, it reacts at all surfaces which includes the substrate, the chamber walls but also the target surface. This is because the chemical reaction that leads to compound formation is highly exothermic, and the excess energy can only be removed by a surface (as a third partner) since three body collisions in magnetron sputtering are rare because of the low reactive gas pressure and low density of the sputtered atoms [3].

The reaction of the reactive gas with the target has a negative effect on the deposition rate and this is illustrated in the figure 2 that shows schematically the deposition rate as a function of the reactive gas flow ϕ [4].