Entendimento químico da adesão de filmes de carbono amorfo em ligas ferrosas por meio de intercamadas contendo silício

Abstract

Diamond-like Carbon films (DLC) films, despite research being developed over four decades, have restricted industrial use and prevent massive application in recent years due to the low adhesion of this material to ferrous alloys. The low adhesion of these films is interpreted by different physical and chemical resources that contribute to the delamination process. The physical mechanisms refer to internal residual stresses caused by ions and atoms bombardment during the deposition process and the difference in thermal expansion of the film and substrate. While the chemical mechanisms involve the chemical affinity between substrate and film. The use of silicon-containing interlayers improves the adhesion of amorphous carbon films, as these interlayers takes the difference of the thermal expansion coefficients between substrate and film provide the properties present in the film/interlayer/substrate interfaces. Interfacial bonds such as C-C and Si-C may promote adhesion due to the use of silicon interlayers, but a better understanding of the interface chemistry of these systems is necessary to introduce the influence of residual elements as oxygen. Contaminating elements from the precursor used in the interlayer deposition process or even atmospheric residual from the chamber's vacuum system, can reduce this chemical affinity and consequently the expected adhesion. Studies have shown positive results for adhesion at temperatures above 300 °C, where the terminating oxygen from bonds is desorbed, but high levels can make the industrial application of these films unfeasible. Other deposition parameters of these interlayers such as deposition time, polarization voltages or even etching can also decrease the presence of elements such as oxygen and optimize the deposition application in temperature at than or equal to 85 °C. In this study, two different systems were proposed in order to analyse the influence of the chemical structure of the silicon-containing interlayer on the adhesion of amorphous carbon films. The different model systems the influence of nitrogen etching in interlayer silicon-containing and the influence of base pressure on pure silicon interlayers to adhere hydrogenated amorphous carbon films to ferrous alloys. The microstructure and chemistry of the film/interlayer/substrate systems were analysed and, subsequently, correlated to adhesion. The structures of the amorphous carbon films were analyzed by Raman spectroscopy. The chemical compositions and connections of the proposed systems included investigations scanning electron microscopy (SEM), glow-discharge optical emission spectroscopy (GD-OES), Fourier transform spectroscopy (FTIR) and X-ray excited photoelectron spectroscopy (XPS). The adhesion was verified through tests governed by international standards such as Scotch test, Mercedes test and scratch test. The systems studied showed the best adhesion of films in systems where the lowest presence of oxygen was verified at the interfaces? interlayer for both models. Therefore, the oxygen is the main element that is harmful to adhesion. A physic-chemical model was proposed to correlate an adhesion with the amount of oxygen present in the deposition. This model can be considered for adhesion of amorphous carbon films, making it available as industrial applications and consequently the application in several areas. [resumo fornecido pelo autor]