Effect of sp3 Content on Adhesion and Tribological Properties of Non-Hydrogenated DLC Films

Abstract

Non-hydrogenated diamond-like carbon (DLC) films with various ratios of sp3/sp2 were prepared on cemented carbide YG8 with DC magnetron sputtering technology. A pure graphite target was selected as the carbon source. Before DLC deposition, a surface etching pretreatment was carried out by mid-frequency magnetron sputtering method, using Ti atoms to improve adhesion strength. The ratios of sp3/sp2 were adjusted by bias voltages. In order to investigate the effect of the ratio of sp3/sp2 on adhesion and tribological properties, Raman spectra, XPS spectra, adhesion scratch test and ball-on-disk dry friction tests were applied. The results indicated that the ratio of sp3/sp2 fluctuated with bias voltage, increasing in the range of 0.74 to 0.98. The adhesion strength decreased from 31.5 to 18.4 N with the increasing ratio of sp3/sp2, while the friction coefficient rose in DLC-Si3N4 and dropped in DLC-Ti6Al4V. For DLC-Ti6Al4V, the oxidation of Ti6Al4V had a greater influence than graphitization of DLC. The hard oxides of Ti6Al4V broke the graphite transfer layer leading to a high friction coefficient. The wear rate was approximately linearly related to bias voltage. The coefficients of the linear regression equation were influenced by different friction materials. The adhesion strength and the friction coefficient were fitted as a function of the ratio of sp3/sp2.

Impact of Plasma Pre-Treatment on the Tribological Properties of DLC Coatings on PDMS Substrates

“…Carbon coatings are a very well investigated material used to improve multiple properties of the surface layer. They can be used to increase hardness [ 1 , 2 , 3 ], improve wear resistance, reduce the coefficient of friction [ 1 , 2 , 3 , 4 , 5 ] and enhance the biocompatibility of the modified surface [ 6 , 7 ] or its resistance to colonisation by micro-organisms [ 7 , 8 ]. Due to their advantages, diamond-like carbon (DLC) coatings are tested in a wide range of applications in very different areas: biomedicine [ 5 , 6 , 7 , 8 , 9 ], machining [ 10 , 11 ], electronics [ 12 , 13 ] and electrochemistry [ 14 , 15 ].…”

Tailored Hydrogen-Free Carbon Films by Tuning the sp2/sp3 Configuration

“…This has attracted much research interest from various application fields, including lubricative or protective coating, electromagnetic wave shielding, sensors, and biology. , In addition, advances in deposition techniques, such as high-power impulse magneto sputtering (HiPIMS), − electron cyclotron resonance sputtering, and unbalanced magnetron sputtering, have facilitated the synthesis of diverse carbon nanostructures, providing greater opportunities for carbon-based applications. In particular, the need for ultrathin a-C coating layers has increased rapidly. ,, However, apart from a few cases, the most reported a-C films have sub-micron thickness, and the spatial resolution of the measurements is limited to a size larger than the carbon nanostructure. ,, Thus, comprehensive and systematic studies on the electrical, mechanical, tribological, and chemical features of ultrathin a-C layers are lacking.…”

“…16,19,25 However, apart from a few cases, the most reported a-C films have sub-micron thickness, and the spatial resolution of the measurements is limited to a size larger than the carbon nanostructure. 15,17,26 Thus, comprehensive and systematic studies on the electrical, mechanical, tribological, and chemical features of ultrathin a-C layers are lacking.…”

Probing Friction Properties of Hydrogen-Free DLC Films in a Nitrogen Environment Based on ReaxFF Molecular Dynamics

“…In earlier works, graphitization of DLC has been employed to explain its tribological mechanism. − The percentage of sp 2 bonded atoms in a DLC film can be used to express the degree of graphitization present because this process involves the conversion of C atoms from sp 3 to sp 2 hybrid bonds. A high level of f sp 2 indicates a higher degree of graphitization, which typically results in a lower friction force F f . − Figure shows that the percentage of sp 3 , sp 2 , and sp 1 bonded C atoms (f sp 3 , f sp 2 , and f sp 1 ) varies with different loadings of F n and the number of nitrogen molecules N n2 . When the load is constant, as illustrated in Figure a and d, with the interaction of the friction interface, the value of f sp 3 will decrease and the value of f sp 2 will increase, which means that the friction interaction will lead to the DLC film’s graphitization.…”