Avaliação dos parâmetros de deposição de intercamada derivada de tetrametilsilano para a adesão de a-C:H em substratos de Ti6Al4V

Abstract

Diamond-like carbon (DLC) is a material composed of carbon in sp2 and sp3 hybridizations, which may or may not contain hydrogen. Its low coefficient of friction, high hardness and chemical inertness make it an interesting material for technological applications. However, the adhesion of DLC films on some metallic substrates is impaired by the low interfacial bond strength and high residual stress. In this case, an interlayer can be used to prevent this problem. The interlayer is a film that binds the DLC and the substrate, and its function is to produce strong interfacial bonds and reduce the coating?s residual stress, enhancing the adhesion. The current research objective was to search for correlations between the deposition parameters, properties of plasma, physicochemical properties of interlayers and adhesion of DLC films, with emphasis on the production of well adhered films. Plasma-enhanced chemical vapor deposition (PECVD) technique with electrostatic confinement was applied to produce the films. In the deposition chamber, Ti6Al4V substrates underwent etching, a-SiCx:H interlayer deposition from tetramethylsilane (TMS), and DLC film deposition. In the 1° sample series, the altered parameters were the presence of hydrogen in the etching and the interlayer deposition temperature. In the 2° sample series, the altered parameter was the interlayer bias voltage. In the 3° sample series, the altered parameter was the H2/Ar flow proportion in the etching. In all steps, the plasma was monitored with optical emission spectroscopy (OES). The DLC film structure and morphology were evaluated by Raman spectroscopy and optical microscopy. The films' thickness was determined by field emission gun scanning electron microscopy (FEG-SEM) and energy dispersive X-ray spectroscopy (EDS). The a-SiCx:H interlayers were chemically analyzed by glow discharge optical emission spectroscopy (GDOES), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The films' adhesion was determined by scratch tests, and the trails were analyzed by EDS. Deposited DLC films are type hydrogenated amorphous carbon (a C:H). A higher interlayer deposition temperature resulted in less oxygen content, associated with a higher a-C:H film adhesion. The interlayer bias voltage affected its growth rate, in a way that the thicker film, with (344 ± 1) nm, was produced by applying 600 V. This phenomenon was attributed to two competing mechanisms: ionization/dissociation and re-sputtering. Higher bias voltages produced interlayers with more carbon and less silicon. The carbon and silicon contents went from (44,83 ± 0,92) %at. and (41,74 ± 0,80) %at. with 400 V to (69,59 ± 0,70) %at. and (21,42 ± 0,61) %at. with 700 V, respectively. The bias voltage did not cause substantial change in the a C:H films? adhesion. Increasing the H2 relative flow until 40% enhanced the a-C:H film's adhesion. At higher H2 relative flows, the adhesion stays constant. It implies that the atomic hydrogen promoted the oxygen removal efficiency of the a-SiCx:H/Ti6Al4V interface, until saturation was reached. [resumo fornecido pelo autor]