From nitride to carbide: control of zirconium-based hard materials film growth and their characterization

High-quality thin films of ZrCyN1-y and the novel tribological material Zr0.8Al0.2CyN1-y have been grown by pulsed reactive crossed-beam laser ablation using Zr and Zr--Al ablation targets, respectively, and a pulsed gas. The gas mixture provided the carbon and nitrogen for the solid-solution films. Control of the stoichiometry (i.e. y) was determined by the relative partial pressures of the nitrogen- and carbon-containing gases. It was found that optimal control of the film chemistry was achieved by using the least thermally reactive gases. In this manner, it was possible to activate the gas species exclusively by collisions in the gas phase with the ablation-plume particles, thereby decoupling the chemistry from surface processes. The films were characterized for their chemical, crystallographic, optical, and tribological properties. All the films had very low impurity levels and a cubic rock salt crystal structure over the entire investigated temperature range between 100 and 600 C. Exceedingly high quality epitaxial films could be grown on MgO(001) at 600 C. Films grown on stainless steel were polycrystalline. The hardness of the films showed a maximum for both sets for stoichiometries predicted by a recent theoretical model for hardness based on band-structure calculations. In addition, all the films had an exceptionally low coefficient of friction versus steel.