Influência do tempo de deposição e da pressão de base em intercamadas contendo silício: promovendo adesão de filmes finos de DLC sobre aço SAE 4140

Abstract

Diamond-like carbon (DLC) is an amorphous material widely used in coatings due to its wide range of properties of interest, such as high hardness, resistance to abrasion, chemical corrosion and wear while having low coefficient of friction. However, the main application disadvantage of DLC is its low adhesion on metallic alloys due to high compressive stresses and low density of established chemical connections. One way around this problem is through the application of silicon-containing adhesion interlayers. In this context, the aim of this work is to evaluate the adhesion of DLC films with different interlayer deposition parameters containing silicon. For this, layers of silicon from the precursor tetramethylsilane were deposited on SAE 4140 steel, and, subsequently, the deposition of the carbonaceous film was performed using the technique of chemical vapor deposition assisted by pulsed plasma. The variation of the interlayer?s deposition time (from 1 to 25 min) and the base pressure (from 5×10-2 to 9×10-5 mbar) and their influences on the properties of the system were evaluated through scanning electron microscopy by field emission, X-ray spectroscopy by energy dispersion, spectroscopy of optical emission by glow discharge, Fourier-transform infrared spectroscopy, Raman spectroscopy, nanohardness, roughness by profilometry, defect density by optical microscopy and scratch test. The results show the presence of three distinct regions in the cross-sectional analysis: a-C:H film, a-SiCx:H interlayer and substrate (SAE 4140 steel) in both deposition series. For the set of samples where the interlayer deposition time was varied, a gradual increase in the silicon contribution is observed as a function of deposition time, in addition to an increasing trend in the density of defects and the ratio of surface defects. The deposited system remained adhered to the samples with interlayers with equal or greater than 5 minutes of deposition time, but no significant variation was identified in the critical loads supported by these coatings. For the set of samples where the base pressure was varied in the deposition, the thickness of the interlayer has a behavior with minimum and maximum similar to a quadratic function and it is observed an increase in the critical load of delamination supported by the film until the second smallest base pressure, consequence of less oxygen and a good Si/C ratio value. [resumo fornecido pelo autor]