RECENT PROGRESS IN HARD NANOCOMPOSITE COATINGS

Abstract

The paper reports on new advanced hard nanocomposite coatings [1-4]. The paper is divided into two parts. The first part of the paper is devoted to the thermal stability of hard nanocomposite coatings and protection of the substrate against oxidation at temperatures above 1000qC. It is well known that the coating nanostructure is a metastable phase. It means that in the case when the temperature T under which the coating is operated achieves or exceeds the crystallization temperature, Tcr, the coating material starts to crystallize. This process results in destruction of the coating nanostructure due to formation of large grains and/or d ue to the change of the crystalline structure of coating. It is a reason why the nanocomposite coatings lose their unique properties and easily oxidize at temperatures T t Tcr. Unique properties of hard nanocomposite coatings including the hard nc-MeN/a-Si3N4 nanocomposite films with low (d10 at.%) Si content, most often produced so far, are thermally stable up to a temperature T | 1000qC only. This temperature is, however, too low for many applications. The thermal stability of nanocomposite coatings above 1000qC is demonstrated on thermal cycling of the magnetron sputtered Si-Zr-O nanocomposite coating [3]. It is shown that the nanocomposite coating is thermally stable as far as its structure does not change during heating and subsequent cooling. This fact is demonstrated by (1) the evolution of structure of the Si-Zr-O composite coating with low amount of Zr (�5 at.%) during thermal cycling from room temperature (RT) to a maximum annealing temperature Ta and subsequent cooling to RT given in Fig.1 and (2) no change of its hardness H and effective Young’s modulus E * during thermal cycling.