Effects of Processing Parameters on Microstructure and Properties of Nanoscale ZrC/ZrB₂ Multilayered Coatings

ZrC/ZrB₂ multilayered coatings with bilayer periods of 3.5--40nm are synthesized by rf magnetron sputtering. Analyses of x-ray diffraction, scanning electron microscopy and nanoindentation indicate that multilayered coatings possess much higher hardness and greater fracture resistance than monolithic ZrC and ZrB₂ coatings. A maximum hardness (41.7GPa) and a critical fracture load (73.7mN) are observed in the multilayer with La=32nm deposited at the substrate bias -40V. Higher residual stress built in the ZrC layer can be released by periodic insertion of ZrB₂ into the ZrC layer. A clear multilayered structure with mixed ZrB₂ (001), ZrB₂ (002) and ZrC (111) orientations should be responsible for the enhanced mechanical properties.