Synthesis of Ti(C, N, O) coatings by unbalanced magnetron sputtering

doi:10.1016/S0924-0136(03)00773-8

Journal of Materials Processing Technology

Volume 140, Issues 1–3, 22 September 2003, Pages 662-667

https://doi.org/10.1016/S0924-0136(03)00773-8 Get rights and content

Abstract

Several TiCNO coatings were deposited using an unbalanced magnetron sputtering system. The composition of C, N, O was first studied using GDOS (glow discharge optical spectrometer). The coating properties as a function of oxygen/nitrogen flow ratio were then studied by using SEM, scratch testing and nano-indentation measurement. The tribological properties of the coatings were then investigated using a ball-on-disk setup with alumina balls. The sliding speeds were set at 10, 20, and 30 cm/min. The results show that coating properties and performance are greatly affected by the flow rate of oxygen. With oxygen flow rate set at 4 sccm during deposition, the TiCNO coating shows the lowest wear rate and friction coefficient among all. Further increase in oxygen flow rate caused a decrease of wear resistance with the increase of friction coefficient. The wear debris were analyzed using Raman spectroscopy. The tribological behavior of the selected TiCNO coating was also compared with other Ti-based hard coatings.

Introduction

Titanium carbonitride (TiC_xN_1−x or Ti(C, N)) coatings are, in general, used to improve tool life by combining the properties of tough TiN and hard TiC. The advantages of these coatings over other coating materials, such as TiN or TiAlN, stem from its superior friction behavior in contact with steel, high hardness and residual stress [1], [2]. Because of their low friction, the coatings are especially durable at low cutting speed [1]. The combined effect of low friction behavior and high residual stress helps to prevent cutting-edge deformation for high speed steels and reduces the risk of cutting-edge chipping on carbide. In addition, the coating’s high hardness provides excellent resistance to wear [2].

To further improve the properties of Ti(C, N) coating, alloying the coating with certain amount of oxygen is hinted by other researchers as a plausible way [3], [4]. The oxygen-containing Ti(C, N) coating (or Ti(C, N, O)) is expected to exhibit a good resistance to oxidation wear and corrosion because of the small atomic size of oxygen and the inertness of oxide, which in turn creates high hardness and compressive stress [5], [6]. However, only few publications in the literature ever discussed the deposition, properties and effectiveness of Ti(C, N, O) coatings. In this paper, Ti(C, N, O) coatings were prepared by unbalanced magnetron sputtering with the variation of oxygen/nitrogen flow ratio. The effects of oxygen content on tribological behaviors were studied and discussed.

Section snippets

Coating deposition

Ti(C, N) and Ti(C, N, O) coatings with various compositions were deposited in a closed field unbalanced reactive DC magnetron sputtering system. Fig. 1 shows the schematic drawing of the system.

The details about the system can be found elsewhere [7]. Polished and cleaned M2 steel disks with a hardness of 63 HRC and dimensions of 50 mm in diameter, 6 mm in thickness were used as the substrates for coating. The base pressure of the chamber is 6.65×10⁻⁴ Pa. The substrates were sputter-cleaned using

Coating properties

Some coatings’ properties including hardness, adhesion, and the tribological behaviors are listed in Table 1 along with the conditions of deposition. From this table, it can be observed that all properties are affected by the variation of O₂/N₂ flow ratios. Especially, when the oxygen flow rate was at 4 sccm (nitrogen flow rate=18 sccm), the hardness and adhesion of Ti(C, N, O) coatings reached their maximum. Further increase in oxygen flow rate would decrease the values of both. Fig. 2 shows the

Conclusions

The synthesis and performance of Ti(C, N, O) coatings prepared in this study are greatly affected by the flow ratios of oxygen to nitrogen. Addition of oxygen could increase the incorporation of nitrogen into the coatings. This is probably caused by the etching effect of carbon on the adsorbed oxygen atoms.

With oxygen flow rate at 4 sccm during deposition, the Ti(C, N, O) coating has the lowest wear rate among all. Further increase in oxygen flow rate caused the decrease of the hardness,

Acknowledgements

We would like to express sincere gratitude to Dr. Zeng Xianting and Ms. Liu Yuchan of Singapore Institute of Manufacturing Technology for their help during this study.

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Synthesis of Ti(C, N, O) coatings by unbalanced magnetron sputtering

Abstract

Introduction

Section snippets

Coating deposition

Coating properties

Conclusions

Acknowledgements

Surf. Coat. Technol.

Surf. Coat. Technol.

Surf. Coat. Technol.

Surf. Coat. Technol.