Direct Fractographic Evaluation of Multilayer CN x /TiN Films by Magnetron Sputtering
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Direct Fractographic Evaluation of Multilayer CNx/TiN Films by Magnetron Sputtering Gongsheng Song1,2, Qiang Fu2, Chunxu Pan1,2, * 1
Suzhou Institute of Wuhan University, Suzhou, 215123, China
2
School of Physics and Technology, Wuhan University, Wuhan, 430072, China
ABSTRACT
In this paper, a multilayer CNx/TiN composite film on high-speed steel substrate was prepared by using a multi-arc assisted DC reactive magnetron sputtering system. The cross-section observations of the fracture surface reveal that the films show a pure cleavage fracture due to its super-high hardness, and the interfacial strength between the film and substrate is associates with the film thickness, i.e., 2μm is a critical thickness for the present deposition. That is to say, there is no disbonding or cracking at the interface when the film thickness is less than 2m, while the interfacial failure is generated if the film thickness is larger than 2m. This direct SEM observation of the fracture surface provides a distinct image for evaluating the mechanical property and also analyzing the failure mechanism of the films.
INTRODUCTION Since the first theoretical prediction of a hypothetical super-hard materials β-C3N4 by Cohn and Liu [1], hundreds of papers have been published on the areas including synthesis [2-4], microstructures [5-7] and applications [8-11]. However, the full crystalline carbon nitride film is not easy to be prepared because of its instability, and in most case, it is in the form of amorphous carbon nitride (α-CNx) with x typically on the order of 0.3-0.4 and the hardness is of only 20-30Gpa. . Thus, pre-treatment (such as HiPIMS pre-treatment [12]) and interface (such as Ti or TiN [13, 14]) was adopted usually to improve the adhesion of carbon nitride coatings on steel substrates. It has been recognized that when a TiN is used as a structure template, the full crystalline CNx/TiN nano-composite films can be prepared with high hardness over 45Gpa [15-18]. This pseudomorphic stabilization is based upon the lattice matches between hexagonal symmetry TiN (111) (a = 0.30 nm) and β-C3N4 (0001) (a = 0.644 nm). The small lattice mismatch (7% for CNx/TiN) may help the nucleation of crystalline β-C3N4. The adhesion strength, fracture toughness and failure mechanism of the CNx/TiN film were mostly concerned due to its applications in microelectronics, wear resistant
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coatings, etc. Generally, these mechanical properties were evaluated by using nano-indentation [13, 19], and theoretical calculations [14, 20]. For instance, Zhou et al. [13] used nano-scaled Ti and TiN as interlayer for preparing ionic nitrogen doped carbon (CNx(N+)) bilayer films at various pulse frequencies by cathode arc technique.The effects of interlayer and pulse frequency on elemental distribution, microst
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