Effect of N2 partial pressure on the microstructure and mechanical properties of magnetron sputtered CrNx films

doi:10.1016/S0257-8972(02)00667-9

Surface and Coatings Technology

Volume 162, Issues 2–3, 20 January 2003, Pages 189-193

https://doi.org/10.1016/S0257-8972(02)00667-9 Get rights and content

Abstract

In this paper, Chromium nitride (CrN_x) thin films were deposited with reactive magnetron sputtering method. EDX, X-ray diffraction and transmission electronic microscopy were employed to characterize their chemical compositions, phases and microstructures. Microhardness and elastic modulus were evaluated using a microhardness tester and the effect of N₂ partial pressure on the composition, phases, microstructure and mechanical properties of CrN_x thin films was investigated. The results show that the phase formation of CrN_x thin films varies from Cr+Cr₂N to single-phase Cr₂N, and then Cr₂N+CrN to nearly single-phase CrN with increasing N₂ partial pressure. The microhardness values of these films make a distribution ranging from HV 21.4 to 27.1 GPa, and when the atom ratio of Cr:N is 1:2 and 1:1, thin film reaches peak hardness values (HV 27.1 and HV 26.8 GPa, respectively), while the elastic modulus is maximal (350 GPa) when single-phase Cr₂N films is formed.

Introduction

Chromium nitride (CrN_x) films have been proposed to be a promising hard coating material owing its high hardness [1], wear, corrosion [2], [3] and high temperature oxidation resistance [4], [5], [6]. It cannot only be used as wear-resistant coatings in metal cutting and forming tools, but be used as corrosion-resistant and decorative materials [7], [8], [9]. Compared with TiN films, which has been widely used as hard, wear-resistant coatings in engineering, CrN_x films has higher hardness, better corrosion resistance and oxidation resistance even at 700 °C [6], [9], [10]. Besides, CrN_x has higher sputtering yield [9], which is preferable for massive produced articles in short process time.

Cr–N binary system films with several preparing methods have been studied for many years [1], [11], among which sputtering offers an attractive alternative [8]. Some studies show that as-deposited Cr–N films usually consist of two kinds of nitrides, Cr₂N (h.c.p.) and CrN (B1–NaCl). It has been shown that depending on the nitrogen flow rate, Cr, Cr+N, Cr+N+Cr₂N, Cr₂N+CrN and CrN phases can be identified [13]. According to the phase diagram of Cr–N system, the stability field of Cr₂N depends on temperature, and varies from 30.3 to 33.3 at.% N. In contrast, the homogeneous range of CrN is very narrow, extending from 49.5 to 50.0 at.%. The region of homogenous Cr₂N is followed by two-phase region of Cr₂N and CrN. The composition of CrN_x is known to vary around the stoichiometric composition [14]. Compared with the fourth and fifth groups, the sixth group of transition metals which Cr belongs to is more difficult to react with nitrogen [12]. To gain single-phase CrN films, a high N₂ partial pressure is needed. Bertrand et al. [1] found that the hardness highly depended on the N content and the crystalline structure of CrN_x films.

In this paper, the influence of N₂ partial pressure on the composition, phases, microstructure, deposition rate and mechanical properties of magnetron sputtered CrN_x films was investigated.

Section snippets

Experimental details

CrN_x thin films were deposited on high speed steel substrates by reactive radio frequency (RF) magnetron sputtering. These substrates were polished with 1 μm diamond paste before ultrasonically cleaned in acetone and alcohol and then mounted on the substrate holder in the vacuum chamber. Before CrN_x films were deposited, all the substrates were heated to 500 °C to dismiss the absorbates at the surface of substrates and then cooled off to room temperature. To improve the adhesion, a metallic Ti

EDS analysis

EDS analysis results are listed in Table 1 which demonstrates that N content in CrN_x films increases with increasing N₂ partial pressure. It can be seen in Fig. 1 that the evolution of the atomic fraction of N vs. the exponentially increasing N₂ partial pressure increases almost linearly. Stoichiometric Cr₂N is formed when N₂ partial pressure is 2–4×10⁻² Pa, while to reach stoichiometric CrN, a very high N₂ partial pressure of 0.3 Pa is needed and then P_Ar:P_N₂=1:1. This result shows that Cr in

Conclusions

1
Using reactive magnetron sputtering method, CrN_x thin films with different N content can be prepared by changing the N₂ partial pressure. The deposition rate, chemical compositions, phase formation, microstructure and corresponding mechanical properties also change with varied N₂ flow rate.
2
Magnetron sputtered Cr₂N films possess high hardness of 27.1 GPa and high elastic modulus of 348 GPa, as well as higher sputtering yield, which make it a promising coating for protective and wear-resistant

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Effect of N2 partial pressure on the microstructure and mechanical properties of magnetron sputtered CrNx films

Abstract

Introduction

Section snippets

Experimental details

EDS analysis

Conclusions

Surf. Coat. Technol.

Thin Solid Films

Surf. Coat. Technol.

Thin Solid Films

Thin Solid Films

Surf. Coat. Technol.

Surf. Coat. Technol.

Effect of N₂ partial pressure on the microstructure and mechanical properties of magnetron sputtered CrN_x films