Structure, mechanical and tribological properties of d.c. magnetron sputtered TiB 2 and TiB 2(N) thin films

Abstract

TiB 2 and TiB 2(N) ceramic compounds may have potential application as protective coatings in the magnetic recording industry, because of their high hardness, wear resistance and chemical stability. In this paper, TiB 2(N) and TiB 2 films were prepared by d.c. magnetron sputtering with and without a nitrogen gas ambient, respectively. The microstructures of these films were examined by X-ray diffractometry and TEM. The mechanical properties of these films were characterized by nano-indentation. Thin film stresses were measured by a wafer curvature technique. The wear volume losses of these films rubbed by a magnetic tape were determined by a sphere-on-flat accelerated wear tester. The results of grazing angle X-ray diffraction and TEM showed that increasing the nitrogen flow rate resulted in a structure change in as-deposited films from (001) textured crystallites to an amorphous microstructure. It was found in nano-indentation and tribological experiments that hardness elastic modulus and wear resistance of these films were significantly improved with an initial incorporation of a small amount of nitrogen. However, further increase of nitrogen resulted in a sharp decrease in these properties in the TiB 2(N) films. The mechanical and tribological properties of the TiB 2 and TiB 2(N) coatings are discussed in terms of the nitrogen content and the film microstructure.