Interface effect on tribological properties of titanium–titanium nitride nanolaminated structures

doi:10.1016/S0257-8972(00)00663-0

Surface and Coatings Technology

Volume 127, Issues 2–3, 22 May 2000, Pages 167-173

https://doi.org/10.1016/S0257-8972(00)00663-0 Get rights and content

Abstract

Nanolaminated titanium–titanium nitride [Ti–TiN]_n structures have been deposited on silicon 〈100〉 substrates by RF reactive sputtering in order to study their mechanical properties. Structures with graded Ti/TiN (interface thickness of approx. 2 nm) and with ultra-thin Ti/TiN interfaces (approx. 0.5 nm) have been investigated with multilayer period thicknesses ranging between 20 and 2.5 nm. The deposition followed by in situ kinetic ellipsometry point out the two types of interfaces. Real period thicknesses, measured by X-ray reflectometry, are close to the expected ones. Thin film X-ray diffraction analysis shows the polycrystalline nature of the nanostuctures. In the superlattice, Ti and TiN individual layers are textured [002] and [111], respectively. Tribological tests, carried out using a CSEM pin-on-disc apparatus, point out that the wear resistance of the samples increase when the period thickness is lowered (same total thickness and growth parameters). For small period thickness, the interface quality has a crucial influence on the wear resistance of the samples. Best tribological properties are observed for samples with ultra-thin interfaces and a period thickness of 2.5 nm.

Introduction

Titanium nitride is broadly used as a hard protective coating for tribological applications [1]. It has been shown that metallic/ceramic or ceramic/ceramic multilayered coatings involving TiN ceramic materials have improved the mechanical performance (hardness and wear resistance) as compared to today’s standard homogeneous TiN coatings [2], [3], [4], [5]. Also, an improvement of wear resistance induced by nanometre scale multilayered coatings has been observed [6], [7], [8]. Nevertheless, the mechanism inducing the improved wear resistance is not yet well understood [8], [9]. At the nanometre scale, when the layer thicknesses are lowered, the interface quality determines the physical properties crucially. The aim of this paper is to present new results concerning the influence of the interface quality of nanolaminated Ti/TiN structures on the wear resistance.

Section snippets

Sample deposition procedure

All films were deposited at room temperature by RF sputtering on commercially available p-type doped single-crystal Si wafers of 〈100〉 orientation using a UHV growth system. The base pressure of the system is 1.33×10⁻⁶ Pa and the working pressures during growth steps were approximately 0.67 Pa. The sputtering target is made of Ti elemental metal. Titanium films were grown using a pure argon plasma, and titanium nitride films with an argon–nitrogen plasma (20% of nitrogen within the total N₂+Ar

Diagnostics

The deposition is followed by in situ kinetic ellipsometry using an incident angle of 72° and a wavelength of 632.8 nm (He–Ne laser). In situ kinetic ellipsometry is a non-destructive optical technique performed by reflecting polarised light from the sample. The light polarisation state changes upon reflection and this change is related to the change of the optical constant of the sample (index of refraction n, and extinction coefficient k). A model constructed to physically describe the sample

In situ kinetic ellipsometry

Kinetic ellipsometry, performed in situ and in real time during film deposition, allows us to observe two types of Ti/TiN interfaces (Ti deposited on TiN) depending on the growth parameters. The TiN/Ti interfaces (TiN deposited on Ti) are always sharp. For all the samples, the first period is strongly perturbed by reactions involving the SiO₂ layer at the substrate surface and the Ti deposited layer.

Tribological properties

In order to have comparable results all the samples have the same total thickness of approximately 300 nm. Fig. 8 shows the number of cycles to failure (number of cycles at which the substrate is first uncovered) obtained from the pin-on-disc experiment vs. Λ for both types of samples (with ultra-thin and with graded interfaces). Several tests have been performed on each specimen and a mean value has been calculated. Most of the samples exhibit an intermediate tribological behaviour between

Conclusion

In situ kinetic ellipsometry has evidence of the existence of two types of interfaces (ultra-thin and graded) between the TiN and Ti layer (in this sense) depending on growth procedure. XRR confirms kinetic ellipsometry results and leads to the determination of real period thicknesses close to the expected ones. XRD shows that in the multilayers Ti and TiN are crystallised and oriented [002] for Ti and [111] for TiN. Tribological experiments have shown the impact of the quality of the

Acknowledgements

The authors would like to thank Gilles Renou of the Laboratoire Multicouches Nanométriques for technical assistance and Michel Jeandin of ENSMP for useful discussions around tribology.

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Interface effect on tribological properties of titanium–titanium nitride nanolaminated structures

Abstract

Introduction

Section snippets

Sample deposition procedure

Diagnostics

In situ kinetic ellipsometry

Tribological properties

Conclusion

Acknowledgements

Surf. Coat. Technol.

Surf. Coat. Technol.

Surf. Coat. Technol.

Thin Solid Films

Surf. Coat. Technol.

Surf. Coat. Technol.

Thin Solid Films