Effect of substrate bias voltage on defect generation and their influence on corrosion and tribological properties of HIPIMS deposited CrN/NbN coatings

Abstract

Substrate bias voltage is one of the most influential deposition parameter for physical vapour deposition processes as it can directly control the adatom mobility during coating growth. It influences the hardness, roughness as well as the microstructure of the coatings. Thus, bias voltage could also affect the defect formation during the coating deposition. High Power Impulse Magnetron Sputtering (HIPIMS) has been proven useful in producing void free and arc droplet free dense coatings. However, such coatings can still suffer from some defects associated with external factors (independent of deposition technique), such as substrate irregularities and the flakes coming from the chamber components. In order to study the effects of bias voltage (U b) on the defect formation during HIPIMS process, four sets of CrN/NbN coatings were deposited at U b =-40 V,-65 V,-100 V and-150 V. Microscopic studies revealed that with the increase in bias voltage the coatings morphology was altered and the percentage of surface area covered by optically visible defects was increased from 3.13 % to 4.30 %. The defects on the coatings deposited at U b =-100 V and-150 V led to preferential corrosive attack resulting in a sharp increase in corrosion current density during Potentiodynamic polarisation experiments. Room temperature pin-on-disc tribological tests exhibited the influence of defects on the wear behaviour; however, the coefficient of friction (µ) values were mainly influenced by the nature of the oxides formed during the tests. Coating microstructure and bilayer thickness, along with the coating defects determined the coefficient of wear (Kc) values. This study revealed that the coating deposited at U b =-65 V had the highest wear resistance (Kc = 2.68 × 10-15 m 3 N-1 m-1) and the lowest friction (µ = 0.48).

On the role of ion potential energy in low energy HiPIMS deposition: An atomistic simulation

“…To the best of our knowledge, in this work we have shown for the first time that such effects can occur due to the ionic potential. The formation of open pores at the surface has also been reported for relatively harder materials, such as CrN and NbN deposited by HiPIMS [75]. Thus, our findings are of general interest for variety of thin film deposition processes.…”

Development and characterization of CrN/CrAlN multilayer coatings deposited by hybrid magnetron sputtering process

“…The curves of corrosion tests and the calculated results, by means of the Tafel Extrapolation Method are shown in Figure 62 and Table 20, respectively. Differently of what was found by Biswas et al (2018b), the coating with more defects presented here the higher corrosion resistance. Of course there are other mechanisms in play.…”

“…According to Biswas et al (2017), these defects are originated by impurities present in the deposition chamber such as dust and flakes from the walls. Furthermore, they proved that the amount of the area occupied by defects is influenced by changing the pressure (BISWAS et al, 2018a) and bias (BISWAS et al, 2018b). Results from periodicity evaluation can be found in Table 18.…”

“…Furthermore, those higher values might provide ion implantation on the substrate, below the surface, which increases the adhesion of the coating (ANDERS, 2014). Biswas et al (2018b) presented in their study a correlation between the applied bias and the quantity of defects on the coatings. Furthermore, they showed that, as the bias was increased, so was the the hardness, the corrosion resistance and the surface roughness.…”

Nitrogen-Enriched Cr1−xAlxN Multilayer-Like Coatings Manufactured by Dynamic Glancing Angle Direct Current Magnetron Sputtering

“…It was demonstrated by [8,31], and [36] that for coatings prepared by DGLAD, the properties were In both Al-containing coatings, it was possible to see round morphological defects of a few microns distributed along the surface. These defects are inherent in the sputtering process and unavoidable to some level [33,34]. We observed that CrN presented finer grains and the addition of Al increased grain size.…”