Thermal Stability and Oxidation Resistance of Nanocomposite TiC/a-C Protective Coatings

Nanocomposite films composed by small crystallites of hard phases embedded in an amorphous lubricant matrix have been extensively studied as protective coatings. These kinds of coatings have often to work in extreme environments, exposed to high temperatures (above 800-900 degrees C), and/or oxidizing/corrosive atmospheres, which may resist. As a result, it is important to study the behavior of such coatings at high temperatures (thermal stability) and in the presence of oxygen (oxidation resistance). In this sense, we have selected a TiC/a-C nanocomposite coating with good mechanical and tribological properties in order to do several thermal tests under three different environments: high vacuum (10(-6) mbar), low vacuum (10(-1) mbar), and air. Our observations allow us to establish that the film microstructure is stable at least up to 1000 degrees C in high vacuum. When oxygen is present, the practical temperature of use is reduced at 700 degrees C (low partial pressure) and 300 degrees C (air) by formation of Ti oxides and C removal