Mechanical and Surface Characterization of Diamond-Like Carbon Coatings onto Polymeric Substrate

Abstract

In this master thesis, diamond-like carbon DLC/Cr bilayer systems, with thickness up to 1278 nm were formed on ABS, glass and Si substrates. Substrates surface were prepared by oxygen plasma cleaning process. The chromium thin film, which acts as a buffer layer, was grown by magnetron sputtering deposition. Diamond-like carbon was deposited by pulsed-DC PECVD, with methane and hydrogen as reactants. A Plackett-Burman experimental design was carried out in order to determine the influence of technological parameters of the deposition process on the thickness, deposition rate, intrinsic stress, contact angle, roughness, friction coefficient and wear rate of the obtained coatings. The independent variables were power, chamber pressure, time of deposition, total flux of the gases, composition of the reactant gases and oxygen plasma cleaning conditions. Values of intrinsic stress between 0.13-0.78 GPa were reported. Wear resistance measurements were performed by grinding calottes with a defined geometry. Low wear rate was achieved in the range of 1E-14 to 1E-15 m^3/Nm. The friction of the obtained coatings under different relative humidities, ranging 20 to 80% in a nitrogen environment, was measured using a nanotribometer with tungsten carbide ball. Results showed that friction coefficient increases with the increasing relativity humidity. Values from 0.12 to 0.24 for friction coefficient were reported. . The main objective of the DLC coating is to improve the wear resistance and tribological behavior of ABS in order to increase his durability for automotive, medical, household and textile applications, among others.